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The article focuses on a study which aims at measuring atmospheric column carbon dioxide (CO2) from a sun photometer in Beijing, China from 2010-2012. In the study, CO2 measurements were acquired, translated into cloud free data, and converted into an index related to column CO2 amount. Seasonal variations of CO2 levels in the atmosphere were also analyzed.

With the process of urbanization in China, the urban waterlogging caused by rainstorms occurs frequently and often leads to serious damage to the natural environment, human life, and the city economy. Rapid detection of rainstorm and urban waterlogging disasters is an essential step to minimize these losses. Weibo, a popular microblog service in China, can provide many real-time Weibo posts for rapid detection. In this paper, we propose a method to identify microblogs with rainstorm and waterlogging information and apply them to waterlogging risk assessment. After pre-processing the microblog texts, we evaluate the performance of clustering (k -means) and classification (support vector machine, SVM) algorithms in the classification task. Apart from word vector features, we also introduce sentiment and publisher features for more real-time and accurate results. Furthermore, we build a waterlogging intensity dictionary to assess the waterlogging risk from the Weibo texts and produce a risk map with ArcGIS. To examine the efficacy of this approach, we collect Weibo data from two rainstorms and waterlogging disasters in Beijing city as examples. The results indicate that the SVM algorithm can be applied for a real-time rainstorm and waterlogging information detection. Compared to official-authentication and personal-certification users, the microblogs posted by general users can better indicate the intensity and timing of rainstorms. The location of waterlogging points is consistent with the risk assessment results, which proves our proposed risk assessment method can be used as a reference for timely emergency response. [ABSTRACT FROM AUTHOR]

Based on the full-diurnal-cycle sodium (Na) lidar observations at Beijing (40.41 ∘ N, 116.01 ∘ E), we report pronounced downward extensions of the Na layer bottomside to below 75 km near mid-December 2014. Considerable Na atoms were observed even as low as ∼ 72 km, where Na atoms are short-lived. More interestingly, an unprecedented Na density of ∼ 2500 atoms cm -3 around 75 km was observed on 17 December 2014. Such high Na atoms concentration was 2 orders of magnitude larger than that normally observed at the similar altitude region. The variations of Na density on the layer bottom were found to be accompanied by warming temperature anomalies and considerable perturbations of minor chemical species (H, O, O 3) in the upper mesosphere. Different from the previous reported metal layer bottom enhancements mainly contributed by photolysis after sunrise, these observational results suggest more critical contributions were made by the Na neutral chemical reactions to the Na layer bottom extensions reported here. The time–longitudinal variations of background atmospheric parameters in the upper mesosphere and stratosphere from global satellite observations and ERA reanalysis data indicated that the anomalous structures observed near the lidar site in mid-December 2014 were associated with planetary wave (PW) activities. The anomalies of temperature and O 3 perturbation showed opposite phase in the altitude range of 70–75 and 35–45 km. This implied that the vertical coupling between the mesosphere and stratosphere, possibly driven by the interactions of PW activities with background atmosphere and modulation of gravity wave (GW) filtering by stratospheric wind, contributed to the perturbations of background atmosphere. Furthermore, the bottom enhancement on 17 December 2014 was also accompanied by clear wavy signatures in the main layer. The strong downwelling regions are likely due to the superposition of tide and GW, suggesting the wave-induced adiabatic vertical motion of the air parcel contributed greatly to the formation of the much stronger Na layer bottom enhancement on 17 December 2014. These results provide a clear observational evidence for the Na layer bottom response to the planetary-scale atmospheric perturbations in addition to tide and GW through affecting the chemical balance. The results of this paper also have implications for the response of the metal layer to vertical coupling between the lower atmosphere and the mesosphere. [ABSTRACT FROM AUTHOR]

The use of multiple digital technologies has addressed conventional exhibition display issues, improving public experience, and aiding in the understanding of historical changes in cultural heritage. This facilitates community sharing and international promotion. Furthermore, the promotion of novel digital application scenarios can encourage the growth of cultural consumption and the digital creativity industry. Beijing's Central Axis is a remarkable and well-preserved example of a traditional central axis in China's capital cities. It is comprised of numerous building complexes and archaeological sites located within the old city. This axis was first constructed in the 13th century, shaped in the 16th century, and continues to thrive today while remaining open to the future. By assessing its dynamic "growth" and "living" value, we have devised an innovative interpretation system plan that includes Augmented Reality Tours, immersive exhibitions in historical buildings, online exhibitions, and a series of public activities. The pilot project, implemented at the Drum Tower located at the northern end of the Central Axis, involved careful restoration and scientific transformation, accurate heritage documentation, and digital reconstruction. Digital creativity empowered and activated the historical building, achieving a comprehensive balance of conservation, utilization, and economics. The exhibition has garnered favorable feedback, particularly from the younger generation, who appreciate the combination of ancient cultural heritage themes and modern digital immersive displays. [ABSTRACT FROM AUTHOR]

The study and control of air pollution involves measuring the structure of the atmospheric boundary layer (ABL) to understand the mechanisms of the interactions occurring between the atmospheric boundary layer and air pollution. Beijing, the capital of China, experienced heavy haze pollution in December 2016, and the city issued its first red-alert air pollution warning of the year (the highest PM 2.5 concentrations were later found to exceed 450 µgm-3). In this paper, the vertical profiles of wind, temperature, humidity and the extinction coefficient (reflecting aerosol concentrations), as well as ABL heights and turbulence quantities under heavy haze pollution conditions, are analyzed, with data collected from lidar, wind profile radar (WPR), radiosondes, a 325 m meteorological tower (equipped with a 7-layer ultrasonic anemometer and 15-layer low-frequency wind, temperature, and humidity sensors) and ground observations. The ABL heights obtained by three different methods based on lidar extinction coefficient data (Hc) are compared with the heights calculated from radiosonde temperature data (Hθ), and their correlation coefficient can reach 72 %. Our results show that Hθ measured on heavy haze pollution days was generally lower than that measured on clean days without pollution, but Hc increased from clean to heavy pollution days. The time changes in friction velocity (u*) and turbulent kinetic energy (TKE) were clearly inversely correlated with PM 2.5 concentration. Momentum and heat fluxes varied very little with altitude. The nocturnal sensible heat fluxes close to the Earth surface always stay positive. In the daytime of the haze pollution period, sensible heat fluxes were greatly reduced within 300 m of the ground. These findings will deepen our understanding of the boundary layer structure under heavy pollution conditions and improve the boundary layer parameterization in numerical models. [ABSTRACT FROM AUTHOR]

As major chemical components of airborne fine particulate matter (PM 2.5), organic carbon (OC) and elemental carbon (EC) have vital impacts on air quality, climate change, and human health. Because OC and EC are closely associated with fuel combustion, it is helpful for the scientific community and policymakers assessing the efficacy of air pollution control measures to study the impact of control measures and regional transport on OC and EC levels. In this study, hourly mass concentrations of OC and EC associated with PM 2.5 were semi-continuously measured from March 2013 to February 2018. The results showed that annual mean OC and EC concentrations declined from 14.0 to 7.7 µgm-3 and from 4.0 to 2.6 µgm-3 , respectively, from March 2013 to February 2018. In combination with the data of OC and EC in previous studies, an obvious decreasing trend in OC and EC concentrations was found, which was caused by clean energy policies and effective air pollution control measures. However, no obvious change in the ratios of OC and EC to the PM 2.5 mass (on average, 0.164 and 0.049, respectively) was recorded, suggesting that inorganic ions still contributed a lot to PM 2.5. Based on the seasonal variations in OC and EC, it appeared that higher OC and EC concentrations were still observed in the winter months, with the exception of winter of 2017–2018. Traffic policies executed in Beijing resulted in nighttime peaks of OC and EC, caused by heavy-duty vehicles and heavy-duty diesel vehicles being permitted to operate from 00:00 to 06:00 (China standard time, UTC + 8, for all times throughout the paper). In addition, the fact that there was no traffic restriction in weekends led to higher concentrations on weekends compared to weekdays. Significant correlations between OC and EC were observed throughout the study period, suggesting that OC and EC originated from common emission sources, such as exhaust of vehicles and fuel combustion. OC and EC levels increased with enhanced SO2 , CO, and NOx concentrations while the O3 and OC levels were enhanced simultaneously when O3 concentrations were higher than 50 µgm-3. Non-parametric wind regression analysis was performed to examine the sources of OC and EC in the Beijing area. It was found that there were distinct hot spots in the northeast wind sector at wind speeds of approximately 0–6 km h -1 , as well as diffuse signals in the southwestern wind sectors. Source areas further away from Beijing were assessed by potential source contribution function (PSCF) analysis. A high-potential source area was precisely pinpointed, which was located in the northwestern and southern areas of Beijing in 2017 instead of solely in the southern areas of Beijing in 2013. This work shows that improvement of the air quality in Beijing benefits from strict control measures; however, joint prevention and control of regional air pollution in the regions is needed for further improving the air quality. The results provide a reference for controlling air pollution caused by rapid economic development in developing countries. [ABSTRACT FROM AUTHOR]

The aim of this study is to characterize the extreme rainfall event on 21-22 July 2012 in Beijing, and its impact on human vulnerability. Based on the available meteorological and rainfall data from Beijing meteorological stations and Surface Weather Observation Stations, the study draws hourly rainfall maps to simulate the rainfall amount and spatial distribution. Using these maps, this paper provides a quantitative analysis of the impact of the temporal and spatial characteristics of rainfall on the vulnerability of three population groups, according to age, gender and total number of victims. The results of three linear regression models indicate the different effects of extreme rainfall parameters on victims with different characteristics. The analysis of victim data in this extreme rainfall event represents the distribution and characteristics of victims in the eight affected districts, and concludes that the "vulnerable group" are males and adults in this extreme rainfall event. This paper is an initial effort to analyze the impact of an extreme rainfall event on the vulnerability of populations with different characteristics quantitatively, which can be used by stakeholders to prioritize the extreme rainfall event impact issues, and develop contingency plans to address and prevent the human and structural damages caused by the extreme rainfall events. [ABSTRACT FROM AUTHOR]

With the process of urbanization in China, the urban waterlogging caused by rainstorm occurs frequently and often leads to considerable damage on natural environment, human life, and the city economy. Rapid detection of rainstorm and urban waterlogging is an essential step to minimize related losses. Weibo, a popular microblogs servicer in China, can provide many real-time Weibo posts for rapid detection. In this paper, we propose a method to identify microblogs with rainstorm and waterlogging information and apply them to waterlogging risk assessment. After pre-processing the microblog texts, we evaluate the performance of clustering (K-means) and classification (support vector machine, SVM) algorithms in the classification task. Apart from the word vector features, we also introduce the sentiment and publisher features for a more real-time and accurate results. Furthermore, we build a waterlogging dictionary to assess the waterlogging risk from the Weibo texts, and get a risk map with ArcGIS. To examine the efficacy, we collect Weibo data from two rainstorm and waterlogging disasters in Beijing city as examples. The results indicate that the SVM algorithm can be applied for real-time rainstorm and waterlogging information detection. Compared to the official authentication and personal certification users, the microblogs posted by general can better show the intensity and timing of rainstorm. The location of waterlogging points is consistent with the risk assessment results, which can be used as a reference for timely emergency response. [ABSTRACT FROM AUTHOR]

The 8.2 ka event has been extensively investigated as a remarkable single event but rarely considered as a part of multi-centennial climatic evolution. Here, we present absolutely dated speleothem multi-proxy records spanning 9.0–7.9 ka from Beijing in North China, near the northern limit of the East Asian summer monsoon (EASM) and thus sensitive to climate change, to provide evidence of the intensified multi-decadal climatic oscillations since 8.52 ka. Three extreme excursions characterized by inter-decadal consecutive δ18 O excursions exceeding ±1σ are identified from 8.52 ka in our speleothem record. The earlier two are characterized by enriched 18 O at ∼8.50 and 8.20 ka, respectively, suggesting a prolonged arid event, which is supported by the positive trend in δ13 C values, increased trace element ratios, and lower growth rate. Following the 8.2 ka event, an excessive rebound immediately emerges in our δ18 O and trace element records but moderate in the δ13 C, probably suggesting pluvial conditions and nonlinear response of the local ecosystem. Following two similar severe droughts at 8.50 and 8.20 ka, the different behavior of δ13 C suggests the recovering degree of resilient ecosystem responding to different rebounded rainfall intensity. A comparison with other high-resolution records suggests that the two droughts–one pluvial pattern between 8.52 and 8.0 ka is of global significance instead of being a regional phenomenon, and is causally linked to the slowdown and acceleration of the Atlantic Meridional Overturning Circulation that was further dominated by the freshwater injections in the North Atlantic. [ABSTRACT FROM AUTHOR]

The total losses caused by natural disasters have spatial heterogeneity due to the different economic development levels inside the disaster-hit areas. This paper uses scenarios of direct economic loss to introduce the sectors' losses caused by the 2008 Wenchuan earthquake (2008 WCE) in Beijing, utilizing the Adaptive Regional Input-Output (ARIO) model and the Inter-regional ripple effect (IRRE) model. The purpose is to assess the ripple effects of indirect economic loss and spatial heterogeneity of both direct and indirect economic loss at the scale of the smallest administrative divisions of China (streets, villages, and towns). The results indicate that the district of Beijing with the most severe indirect economic loss is the Chaoyang District; the finance and insurance industry (15, see Table 1) of Chaowai Street suffers the most in the Chaoyang District, which is 1.46 times that of its direct economic loss. During 2008-2014, the average annual GDP (gross domestic product) growth rate of Beijing was decreased 3.63% by the catastrophe. Compared with the 8% of GDP growth rate target, the decreasing GDP growth rate is a significant and noticeable economic impact, and it can be efficiently mitigated by increasing rescue effort and by supporting the industries which are located in the seriously damaged regions. [ABSTRACT FROM AUTHOR]

The accessibility of emergency medical services (EMSs) is not only determined by the distribution of emergency medical facilities but is also influenced by weather conditions. Inclement weather could affect the efficiency of the city's traffic network and further affect the response time of EMSs, which could therefore be an essential impact factor on the safety of human lives. This study proposes an EMSs-accessibility quantification method based on selected indicators, explores the influence of inclement weather on EMSs accessibility, and identifies the hotspots that have difficulty accessing timely EMSs. A case study was implemented in Beijing, which is a typical megacity in China, based on the ground-truth traffic data of the whole city in 2019. The results show that inclement weather has a general negative impact on EMSs accessibility. Under an inclement weather scenario, the area in the city that could get EMSs within 15 min would decrease by 13 % compared with a normal scenario (the average state of weekdays without precipitation), while in some suburban townships, the population that could get 15 min EMSs would decrease by 40 %. We found that snowfall has a greater impact on the accessibility of EMSs than rainfall. Although on the whole, the urban area would have more traffic speed reduction, towns in suburban areas with lower baseline EMSs accessibility are more vulnerable to inclement weather. Under the worst scenario in 2019, 12.6 % of the population (about 3.5 million people) could not get EMSs within 15 min, compared with 7.5 % with normal weather conditions. This study could provide a scientific reference for city planning departments to optimize traffic under inclement weather and the site selection of emergency medical facilities. [ABSTRACT FROM AUTHOR]

Abstract. In order to quantify the aerosol impact on climate, a range of aerosol parameters are required. In this paper, two-year of ground-based observations of aerosol optical properties from an urban site in Beijing of China are assessed. The aerosol absorption coefficient (σα), scattering coefficient (σs ), as well as single scattering albedo (ω) are analyzed to aid in characterizing Beijing's urban aerosol. Two-year averages (and standard deviations) for σα at 532 nm, σs at 525 nm and ω at 525 nm are 56±49Mm-1, 288±281Mm-1 and 0.80±0.09, respectively. Meanwhile, there is a distinct diurnal variation for σα, with its minimum occurring at approximately 14:00 to 15:00 and maximum at midnight. σs peaks in the late morning and the minimum occurs in the evening. σs in summer is higher than that in winter. ! is also higher in summer than that in winter, except before 07:00 a.m., and peaks in the early afternoon. Both σα and σs show strong dependence on local wind in all four seasons. When the wind blows from the north with low speed (0-2 m/s), the values of σα are high, and in contrast, very low with wind speeds higher than 4 m/s. When the wind blows from south with low speed (0-4 m/s), σα is intermediate. The patterns of the wind dependence of σα indicates that σα is mainly dominated by local emissions. σs displays a similar dependence on wind speed and direction to σα, except in summer. In summer, the σs value is highest when wind is from southeast with speed of 0-6 m/s. This indicates that the particle pollution resulting from regional transport is only significant in the summer season. ω also shows wind dependence to some extent though not as strong as σα or σs . Overall, the wind dependence results provide valuable information about the locations of aerosol pollution sources and suggest that the air pollution in summer is a regional problem but in other seasons it is mainly affected by local urban emissions. [ABSTRACT FROM AUTHOR]

The concentrations of fine particulate matter (PM) and ozone in Beijing often exceed healthful levels in recent years, therefore China is to taking steps to improve Beijing's air quality for the 2008 Olympic Games. In this paper, the Models-3 Community Multiscale Air Quality (CMAQ) Modeling System was used to investigate a heavy air pollution episode in Beijing during 3-7 April 2005 to obtain the basic information of how heavy air pollution formed and the contributions of local sources and surround emissions. The modeling domain covered from East Asia with four nested grids with 81 to 3 km horizontal resolution focusing on urban Beijing. This was coupled with a regional emissions inventory with a 10 km resolution and a local 1 km Beijing emissions database. The trend of predicted concentrations of various pollutants agreed reasonably well with the observations and captured the main features of this heavy pollution episode. The simulated column concentration distribution of PM was correlated well with the MODIS remote sensing products. Control runs with and without Beijing emissions were conducted to quantify the contributions of non-Beijing sources (NBS) to the Beijing local air pollution. The contributions of NBS to each species differed spatially and temporally with the order of PM2.5>PM10>SO2> soil for this episode. The percentage contribution of NBS to fine particle (PM2.5) in Beijing was averaged about 39%, up to 53% at the northwest of urban Beijing and only 15% at southwest. The spatial distribution of NBS contributions for PM10 was similar to that for PM2.5, with a slightly less average percentage of about 30%. The average NBS contributions for SO2 and soil (diameter between 2.5µm and 10µm) were 18% and 10%. In addition, the pollutant transport flux was calculated and compared at different levels to investigate transport pathway and magnitude. It was found that the NBS contribution correlated with the transport flux, contributing 60% of PM10 concentration in Beijing at the time of transport flux peak during a strong episode with a transport path from southwest to northeast. [ABSTRACT FROM AUTHOR]

On-road ammonia (NH 3) emissions play a significant role in fine particulate matter (PM 2.5) formation in urban areas, posing severe risks for human health. Limited studies have depicted the spatial and temporal variations of on-road NH 3 emissions, in particular lacking detailed quantification of their contributions within densely populated areas. In this study, we established a comprehensive vehicular NH 3 emission model and compiled a gridded on-road NH 3 emission inventory with high spatial (3 km × 3 km) and temporal (monthly) resolution for mainland China. China's annual vehicular NH 3 emissions are estimated to increase from 32.8 ± 1.7 to 87.1 ± 37.5 kt during the period of 2000–2019. Vehicular NH 3 emissions are significantly concentrated in densely populated areas, where agricultural emissions have relatively lower intensity. It is found that vehicular NH 3 emissions could exceed agricultural emissions in the grids containing 23.0 ± 2.1 % of the Chinese population in 2019 (approximately 326.6 ± 25.4 million people), and this ratio is up to 29.4 ± 3.0 % in winter. For extremely populous megacities such as Beijing and Shanghai, vehicular NH 3 emissions exceed agricultural emissions, where 69.2 ± 1.2 % and 72.0 ± 1.3 % of the population resides, respectively. Thus, the significant role of on-road NH 3 emissions in populated areas may have been underappreciated. This study gave a better insight into the absolute value and relative importance of on-road NH 3 emissions for different regions, seasons and population densities in China; this is important in terms of the implications for air quality. [ABSTRACT FROM AUTHOR]

Aerosol pH is a fundamental property of aerosols in terms of atmospheric chemistry and its impact on air quality, climate, and health. Precise estimation of aerosol pH in chemical transport models (CTMs) is critical for aerosol modeling and thus influences policy development that partially relies on results from model simulations. We report the Weather Research and Forecasting Model coupled with Chemistry (WRF-Chem) simulated PM 2.5 pH over China during a period with heavy haze episodes in Beijing, and explore the sensitivity of the modeled aerosol pH to factors including emissions of nonvolatile cations (NVCs) and NH 3 , aerosol phase state assumption, and heterogeneous production of sulfate. We find that default WRF-Chem could predict spatial patterns of PM 2.5 pH over China similar to other CTMs, but with generally lower pH values, largely due to the underestimation of alkaline species (NVCs and NH 3) and the difference in thermodynamic treatments between different models. Increasing NH 3 emissions in the model would improve the modeled pH in comparison with offline thermodynamic model calculations of pH constrained by observations. In addition, we find that the aerosol phase state assumption and heterogeneous sulfate production are important in aerosol pH predictions for regions with low relative humidity (RH) and high anthropogenic SO 2 emissions, respectively. These factors should be better constrained in model simulations of aerosol pH in the future. Analysis of the modeled temporal trend of PM 2.5 pH in Beijing over a haze episode reveals a clear decrease in pH from 5.2 ± 0.9 in a clean period to 3.6 ± 0.5 in a heavily polluted period. The increased acidity under more polluted conditions is largely due to the formation and accumulation of secondary species including sulfuric acid and nitric acid, even though being modified by alkaline species (NVCs, NH 3). Our result suggests that NO 2 oxidation is unlikely to be important for heterogeneous sulfate production during the Beijing haze as the effective pH for NO 2 oxidation of S(IV) is at a higher pH of ∼ 6. [ABSTRACT FROM AUTHOR]

PM 2.5 , generated via both direct emission and secondary formation, can have varying environmental impacts due to different physical and chemical properties of its components. However, traditional methods to quantify different PM 2.5 components are often based on online or offline observations and numerical models, which are generally high economic cost- or labor-intensive. In this study, we develop a new method, named Multi-Tracer Estimation Algorithm (MTEA), to identify the primary and secondary components from routine observation of PM 2.5. By comparing with long-term and short-term measurements of aerosol chemical components in China and the United States, it is proven that MTEA can successfully capture the magnitude and variation of the primary PM 2.5 (PPM) and secondary PM 2.5 (SPM). Applying MTEA to the China National Air Quality Network, we find that (1) SPM accounted for 63.5 % of the PM 2.5 in cities in southern China on average during 2014–2018, while the proportion dropped to 57.1 % in the north of China, and at the same time the secondary proportion in regional background regions was ∼ 19 % higher than that in populous regions; (2) the summertime secondary PM 2.5 proportion presented a slight but consistent increasing trend (from 58.5 % to 59.2 %) in most populous cities, mainly because of the recent increase in O 3 pollution in China; (3) the secondary PM 2.5 proportion in Beijing significantly increased by 34 % during the COVID-19 lockdown, which might be the main reason for the observed unexpected PM pollution in this special period; and finally, (4) SPM and O 3 showed similar positive correlations in the Beijing-Tianjin-Hebei (BTH) and Yangtze River Delta (YRD) regions, but the correlations between total PM 2.5 and O 3 in these two regions, as determined from PPM levels, were quite different. In general, MTEA is a promising tool for efficiently estimating PPM and SPM, and has huge potential for future PM mitigation. [ABSTRACT FROM AUTHOR]

We compare Community Multiscale Air Quality (CMAQ) model predictions with measured nitrous acid (HONO) concentrations in Beijing, China, for December 2015. The model with the existing HONO chemistry in CMAQ severely underestimates the observed HONO concentrations with a normalized mean bias of - 97 %. We revise the HONO chemistry in the model by implementing six additional heterogeneous reactions in the model: the reaction of nitrogen dioxide (NO 2) on ground surfaces, the reaction of NO 2 on aerosol surfaces, the reaction of NO 2 on soot surfaces, the photolysis of aerosol nitrate, the nitric acid displacement reaction, and the hydrochloric acid displacement reaction. The model with the revised chemistry substantially increases HONO predictions and improves the comparison with observed data with a normalized mean bias of - 5 %. The photolysis of HONO enhances daytime hydroxyl radical by almost a factor of 2. The enhanced hydroxyl radical concentrations compare favorably with observed data and produce additional sulfate via the reaction with sulfur dioxide, aerosol nitrate via the reaction with nitrogen dioxide, and secondary organic aerosols via the reactions with volatile organic compounds. The additional sulfate stemming from revised HONO chemistry improves the comparison with observed concentration; however, it does not close the gap between model prediction and the observation during polluted days. [ABSTRACT FROM AUTHOR]

Gaseous hydrochloric (HCl) and hydrobromic acid (HBr) are vital halogen species that play essential roles in tropospheric physicochemical processes. Yet, the majority of the current studies on these halogen species were conducted in marine or coastal areas. Detection and source identification of HCl and HBr in inland urban areas remain scarce, thus limiting the full understanding of halogen chemistry and potential atmospheric impacts in the environments with limited influence from the marine sources. Here, both gaseous HCl and HBr were concurrently measured in urban Beijing, China, during winter and early spring of 2019. We observed significant HCl and HBr concentrations ranging from a minimum value at 1 × 10 8 molecules cm -3 (4 ppt) and 4 × 10 7 molecules cm -3 (1 ppt) up to 6 × 10 9 molecules cm -3 (222 ppt) and 1 × 10 9 molecules cm -3 (37 ppt), respectively. The HCl and HBr concentrations are enhanced along with the increase of atmospheric temperature, UVB and levels of gaseous HNO 3. Based on the air mass analysis and high correlations of HCl and HBr with the burning indicators (HCN and HCNO), gaseous HCl and HBr are found to be related to anthropogenic burning aerosols. The gas–particle partitioning may also play a dominant role in the elevated daytime HCl and HBr. During the daytime, the reactions of HCl and HBr with OH radicals lead to significant production of atomic Cl and Br, up to 2 × 10 4 molecules cm -3 s -1 and 8 × 10 4 molecules cm -3 s -1 , respectively. The production rate of atomic Br (via HBr + OH) is 2–3 times higher than that of atomic Cl (via HCl + OH), highlighting the potential importance of bromine chemistry in the urban area. On polluted days, the production rates of atomic Cl and Br are faster than those on clean days. Furthermore, our observations of elevated HCl and HBr may suggest an important recycling pathway of halogen species in inland megacities and may provide a plausible explanation for the widespread halogen chemistry, which could affect the atmospheric oxidation in China. [ABSTRACT FROM AUTHOR]

In recent years, China has promulgated the "Civil Code of the People's Republic of China", "Implementation Rules of the Provisional Regulations on Real Estate Registration" and other laws and regulations, which have protected citizens' rights and obligations in real estate from the legal system. It shows that the quality of real estate registration data is very important. At present, there is no set of standards for evaluating the quality of real estate registration data. This article sorts out the production process of real estate registration data and focuses on the four stages of production: digitization results, field surveys and surveying and mapping results, group building results, integration and association. As a result, the main points of real estate registration data quality control were put forward, and a quality evaluation model was developed. Taking Beijing's real estate registration historical archives integrated data quality inspection as an application case, it shows that the quality evaluation model has been successfully applied to actual projects, ensuring the quality of Beijing real estate registration data. It also provides a reference for the next step in China's quality control of the unified registration of natural resources confirmation. [ABSTRACT FROM AUTHOR]

Air pollution is a major issue in China and one of the largest threats to public health. We investigated future changes in atmospheric circulation patterns associated with haze events in the Beijing region and the severity of haze events during these circulation conditions from 2015 to 2049 under two different aerosol scenarios: a maximum technically feasible aerosol reduction (MTFR) and a current legislation aerosol scenario (CLE). In both cases greenhouse gas emissions follow the Representative Concentration Pathway 4.5 (RCP4.5). Under RCP4.5 with CLE aerosol the frequency of circulation patterns associated with haze events increases due to a weakening of the East Asian winter monsoon via increased sea level pressure over the North Pacific. The rapid reduction in anthropogenic aerosol and precursor emissions in MTFR further increases the frequency of circulation patterns associated with haze events, due to further increases in the sea level pressure over the North Pacific and a reduction in the intensity of the Siberian high. Even with the aggressive aerosol reductions in MTFR periods of poor visibility, represented by above-normal aerosol optical depth (AOD), still occur in conjunction with haze-favorable atmospheric circulation. However, the winter mean intensity of poor visibility decreases in MTFR, so that haze events are less dangerous in this scenario by 2050 compared to CLE and relative to the current baseline. This study reveals the competing effects of aerosol emission reductions on future haze events through their direct contribution to pollutant source and their influence on the atmospheric circulation. A compound consideration of these two impacts should be taken in future policy making. [ABSTRACT FROM AUTHOR]

Satellite aerosol products such as the Dark Target (DT) produced from the MODerate resolution Imaging Spectroradiometer (MODIS) are useful for monitoring the progress of air pollution. Unfortunately, the DT often fails to retrieve during the heaviest aerosol events as well as the more moderate events in winter. Some of the literature attributes this lack of retrieval to the cloud mask. However, we found this lack of retrieval is mainly traced to thresholds used for masking of inland water and snow. Modifications to these two masks greatly increase 50 % of the retrievals of aerosol optical depth at 0.55 µ m (AOD) greater than 1.0. The "extra"-high-AOD retrievals tend to be biased when compared with a ground-based sun photometer (AErosol RObotic NETwork, AERONET). Reducing bias in new retrievals requires two additional steps. One is an update to the assumed aerosol optical properties (aerosol model); the haze in this region is both less absorbing and lower in altitude than what is assumed in the global algorithm. The second is accounting for the scale height of the aerosol, specifically that the heavy-aerosol events in the region are much closer to the surface than what is assumed by the global DT algorithm. The resulting combination of modified masking thresholds, new aerosol model, and lower aerosol layer scale height was applied to 3 months of MODIS observations (January–March 2013) over eastern China. After these two additional steps are implemented, the significant increase in new retrievals introduces no overall bias at a high-AOD regime but does degrade other overall validation statistics. We also find that the research algorithm is able to identify additional pollution events that AERONET instruments may not due to different spatial sampling. Mean AOD retrieved from the research algorithm increases from 0.11 to 0.18 compared to values calculated from the operational DT algorithm during January to March of 2013 over the study area. But near Beijing, where the severe pollution occurs, the new algorithm increases AOD by as much as 3.0 for each 0.5 ∘ grid box over the previous operational-algorithm values. [ABSTRACT FROM AUTHOR]

Fine particles were sampled from 9 November to 11 December 2016 and 22 May to 24 June 2017 as part of the Atmospheric Pollution and Human Health in a Chinese Megacity (APHH-China) field campaigns in urban Beijing, China. Inorganic ions, trace elements, organic carbon (OC), elemental carbon (EC), and organic compounds, including biomarkers, hopanes, polycyclic aromatic hydrocarbons (PAHs), n -alkanes, and fatty acids, were determined for source apportionment in this study. Carbonaceous components contributed on average 47.2 % and 35.2 % of total reconstructed PM2.5 during the winter and summer campaigns, respectively. Secondary inorganic ions (sulfate, nitrate, ammonium; SNA) accounted for 35.0 % and 45.2 % of total PM2.5 in winter and summer. Other components including inorganic ions (K+ , Na+ , Cl-), geological minerals, and trace metals only contributed 13.2 % and 12.4 % of PM2.5 during the winter and summer campaigns. Fine OC was explained by seven primary sources (industrial and residential coal burning, biomass burning, gasoline and diesel vehicles, cooking, and vegetative detritus) based on a chemical mass balance (CMB) receptor model. It explained an average of 75.7 % and 56.1 % of fine OC in winter and summer, respectively. Other (unexplained) OC was compared with the secondary OC (SOC) estimated by the EC-tracer method, with correlation coefficients (R2) of 0.58 and 0.73 and slopes of 1.16 and 0.80 in winter and summer, respectively. This suggests that the unexplained OC by the CMB model was mostly associated with SOC. PM2.5 apportioned by the CMB model showed that the SNA and secondary organic matter were the two highest contributors to PM2.5. After these, coal combustion and biomass burning were also significant sources of PM2.5 in winter. The CMB results were also compared with results from the positive matrix factorization (PMF) analysis of co-located aerosol mass spectrometer (AMS) data. The CMB model was found to resolve more primary organic aerosol (OA) sources than AMS-PMF, but the latter could apportion secondary OA sources. The AMS-PMF results for major components, such as coal combustion OC and oxidized OC, correlated well with the results from the CMB model. However, discrepancies and poor agreements were found for other OC sources, such as biomass burning and cooking, some of which were not identified in AMS-PMF factors. [ABSTRACT FROM AUTHOR]

China has made great efforts to monitor and control air pollution in the past decade. Comprehensive characterization and understanding of pollutants in three-dimensions are, however, still lacking. Here, we used data from an observation network consisting of 13 aerosol lidars and more than 1000 ground observation stations combined with a data assimilation technique to conduct a comprehensive analysis of extreme heavy aerosol pollution (HAP) over the North China Plain (NCP) from November–December 2017. During the studied period, the maximum hourly mass concentration of surface PM 2.5 reached ∼390 µ g m -3. After assimilation, the correlation between model results and the independent observation sub-dataset was ∼50 % higher than that without the assimilation, and the root mean square error was reduced by ∼40 %. From pollution development to dissipation, we divided the HAP in the NCP (especially in Beijing) into four phases: an early phase (EP), a transport phase (TP), an accumulation phase (AP), and a removal phase (RP). We then analyzed the evolutionary characteristics of PM 2.5 concentration during different phases on the surface and in 3-D space. We found that the particles were mainly transported from south to north at a height of 1–2 km (during EP and RP) and near the surface (during TP and AP). The amounts of PM 2.5 advected into Beijing with the maximum transport flux intensity (TFI) were through the pathways in the relative order of the southwest > southeast > east pathways. The dissipation of PM 2.5 in the RP stage (with negative TFI) was mainly from north to south with an average transport height of ∼1 km above the surface. Our results quantified the multi-dimensional distribution and evolution of PM 2.5 concentration over the NCP, which may help policymakers develop efficient air pollution control strategies. [ABSTRACT FROM AUTHOR]

Smartphones are increasingly being equipped with atmospheric measurement sensors providing huge auxiliary resources for global observations. Although China has the highest number of cell phone users, there is little research on whether these measurements provide useful information for atmospheric research. Here, for the first time, we present the global spatial and temporal variation in smartphone pressure measurements collected in 2016 from the Moji Weather app. The data have an irregular spatiotemporal distribution with a high density in urban areas, a maximum in summer and two daily peaks corresponding to rush hours. With the dense dataset, we have developed a new bias-correction method based on a machine-learning approach without requiring users' personal information, which is shown to reduce the bias of pressure observation substantially. The potential application of the high-density smartphone data in cities is illustrated by a case study of a hailstorm that occurred in Beijing in which high-resolution gridded pressure analysis is produced. It is shown that the dense smartphone pressure analysis during the storm can provide detailed information about fine-scale convective structure and decrease errors from an analysis based on surface meteorological-station measurements. This study demonstrates the potential value of smartphone data and suggests some future research needs for their use in atmospheric science. [ABSTRACT FROM AUTHOR]

Black carbon (BC) forms an important component of particulate matter globally, due to its impact on climate, the environment and human health. Identifying and quantifying its emission sources are critical for effective policymaking and achieving the desired reduction in air pollution. In this study, we present the first direct measurements of urban BC fluxes using eddy covariance. The measurements were made over Beijing within the UK-China Air Pollution and Human Health (APHH) winter 2016 and summer 2017 campaigns. In both seasons, the mean measured BC mass (winter: 5.49 ng m -2 s -1 , summer: 6.10 ng m -2 s -1) and number fluxes (winter: 261.25 particles cm -2 s -1 , summer: 334.37 particles cm -2 s -1) were similar. Traffic was determined to be the dominant source of the BC fluxes measured during both seasons. The total BC emissions within the 2013 Multi-resolution Emission Inventory for China (MEIC) are on average too high compared to measured fluxes by a factor of 58.8 (winter) and 47.2 (summer). Only a comparison with the MEIC transport sector shows that emissions are also larger (factor of 37.5 in winter and 37.7 in summer) than the measured flux. Emission ratios of BC / NO x and BC / CO are comparable to vehicular emission control standards implemented in January 2017 for gasoline (China 5) and diesel (China V) engines, indicating a reduction of BC emissions within central Beijing, and extending this to a larger area would further reduce total BC concentrations. [ABSTRACT FROM AUTHOR]

In the past decade, average PM 2.5 concentrations decreased rapidly under the strong pollution control measures in major cities in China; however, ozone (O3) pollution emerged as a significant problem. Here we examine a unique (for China) 12-year data set of ground-level O3 and precursor concentrations collected at an urban site in Beijing (PKUERS, campus of Peking University), where the maximum daily 8 h average (MDA8) O3 concentration and daytime Ox (O3+NO2) concentration in August increased by 2.3±1.2 ppbv (+3.3±1.8 %) yr -1 and 1.4±0.6 (+1.9±0.8 %) yr -1 , respectively, from 2005 to 2016. In contrast, daytime concentrations of nitrogen oxides (NOx) and the OH reactivity of volatile organic compounds (VOCs) both decreased significantly. Over this same time, the decrease of particulate matter (and thus the aerosol optical depth) led to enhanced solar radiation and photolysis frequencies, with near-surface J(NO2) increasing at a rate of 3.6±0.8 % yr -1. We use an observation-based box model to analyze the combined effect of solar radiation and ozone precursor changes on ozone production rate, P(O3). The results indicate that the ratio of the rates of decrease of VOCs and NOx (about 1.1) is inefficient in reducing ozone production in Beijing. P(O3) increased during the decade due to more rapid atmospheric oxidation caused to a large extent by the decrease of particulate matter. This elevated ozone production was driven primarily by increased actinic flux due to PM 2.5 decrease and to a lesser extent by reduced heterogeneous uptake of HO2. Therefore, the influence of PM 2.5 on actinic flux and thus on the rate of oxidation of VOCs and NOx to ozone and to secondary aerosol (i.e., the major contributor to PM 2.5) is important for determining the atmospheric effects of controlling the emissions of the common precursors of PM 2.5 and ozone when attempting to control these two important air pollutants. [ABSTRACT FROM AUTHOR]

In this study, we present O3 retrievals from ground-based Fourier transform infrared (FTIR) solar absorption measurements between June 2018 and December 2019 at Xianghe, China (39.75 ∘ N, 116.96 ∘ E). The FTIR spectrometer at Xianghe is operated with indium gallium arsenide (InGaAs) and indium antimonide (InSb) detectors, recording the spectra between 1800 and 11 000 cm -1. As the harmonized FTIR O3 retrieval strategy within the Network for the Detection of Atmospheric Composition Change (NDACC) uses the 1000 cm -1 spectral range, we apply the O3 retrieval in the 3040 cm -1 spectral range at Xianghe. The retrieved O3 profile is mainly sensitive to the vertical range between 10 and 40 km, and the degrees of freedom for signal is 2.4±0.3 (1σ), indicating that there are two individual pieces of information in partial columns between the surface and 20 km and between 20 and 40 km. According to the optimal estimation method, the systematic and random uncertainties of the FTIR O3 total columns are about 13.6 % and 1.4 %, respectively. The random uncertainty is consistent with the observed daily standard deviation of the FTIR retrievals. To validate the FTIR O3 total and partial columns, we apply the same O3 retrieval strategy at Maïdo, Réunion (a.k.a. Reunion Island; 21.08 ∘ N, 55.38 ∘ E). The FTIR O3 (3040 cm -1) measurements at Xianghe and Maïdo are then compared with the nearby ozonesondes at Beijing (39.81 ∘ N, 116.47 ∘ E) and at Gillot (20.89 ∘ S, 55.53 ∘ E), respectively, as well as with co-located TROPOspheric Monitoring Instrument (TROPOMI) satellite measurements at both sites. In addition at Maïdo, we compare the FTIR O3 (3040 cm -1) retrievals with the standard NDACC FTIR O3 measurements using the 1000 cm -1 spectral range. It was found that the total columns retrieved from the FTIR O3 3040 cm -1 measurements are underestimated by 5.5 %–9.0 %, which is mainly due to the systematic uncertainty in the partial column between 20 and 40 km (about -10.4 %). The systematic uncertainty in the partial column between surface and 20 km is relatively small (within 2.4 %). By comparison with other measurements, it was found that the FTIR O3 (3040 cm -1) retrievals capture the seasonal and synoptic variations of the O3 total and two partial columns very well. Therefore, the ongoing FTIR measurements at Xianghe can provide useful information on the O3 variations and (in the future) long-term trends. [ABSTRACT FROM AUTHOR]

Severe winter haze accompanied by high concentrations of fine particulate matter (PM 2.5) occurs frequently in the North China Plain and threatens public health. Organic matter (OM) and sulfate are recognized as major components of PM 2.5 , while atmospheric models often fail to predict their high concentrations during severe winter haze due to incomplete understanding of secondary aerosol formation mechanisms. By using a novel combination of single-particle mass spectrometry and an optimized ion chromatography method, here we show that hydroxymethanesulfonate (HMS), formed by the reaction between formaldehyde (HCHO) and dissolved SO2 in aerosol water, is ubiquitous in Beijing during winter. The HMS concentration and the molar ratio of HMS to sulfate increased with the deterioration of winter haze. High concentrations of precursors (SO2 and HCHO) coupled with low oxidant levels, low temperature, high relative humidity, and moderately acidic pH facilitate the heterogeneous formation of HMS, which could account for up to 15 % of OM in winter haze and lead to up to 36 % overestimates of sulfate when using traditional ion chromatography. Despite the clean air actions having substantially reduced SO2 emissions, the HMS concentration and molar ratio of HMS to sulfate during severe winter haze increased from 2015 to 2016 with the growth in HCHO concentration. Our findings illustrate the significant contribution of heterogeneous HMS chemistry to severe winter haze in Beijing, which helps to improve the prediction of OM and sulfate and suggests that the reduction in HCHO can help to mitigate haze pollution. [ABSTRACT FROM AUTHOR]

A vast area in China is currently going through severe haze episodes with drastically elevated concentrations of PM 2.5 in winter. Nitrate and sulfate are the main constituents of PM 2.5 , but their formations via NO2 and SO2 oxidation are still not comprehensively understood, especially under different pollution or atmospheric relative humidity (RH) conditions. To elucidate formation pathways of nitrate and sulfate in different polluted cases, hourly samples of PM 2.5 were collected continuously in Beijing during the wintertime of 2016. Three serious pollution cases were identified reasonably during the sampling period, and the secondary formations of nitrate and sulfate were found to make a dominant contribution to atmospheric PM 2.5 under the relatively high RH condition. The significant correlation between NOR, NOR = NO3-/(NO3-+NO2) , and [NO2]2 × [O3] during the nighttime under the RH≥60 % condition indicated that the heterogeneous hydrolysis of N2O5 involving aerosol liquid water was responsible for the nocturnal formation of nitrate at the extremely high RH levels. The more often coincident trend of NOR and [HONO] × [DR] (direct radiation) × [ NO2 ] compared to its occurrence with [Dust] × [ NO2 ] during the daytime under the 30 % < RH < 60 % condition provided convincing evidence that the gas-phase reaction of NO2 with OH played a pivotal role in the diurnal formation of nitrate at moderate RH levels. The extremely high mean values of SOR, SOR = SO42-/(SO42-+SO2) , during the whole day under the RH≥60 % condition could be ascribed to the evident contribution of SO2 aqueous-phase oxidation to the formation of sulfate during the severe pollution episodes. Based on the parameters measured in this study and the known sulfate production rate calculation method, the oxidation pathway of H2O2 rather than NO2 was found to contribute greatly to the aqueous-phase formation of sulfate. [ABSTRACT FROM AUTHOR]

Secondary aerosol constitutes a large fraction of fine particles in urban air of China. However, its formation mechanisms and atmospheric processes remain largely uncertain despite considerable study in recent years. To elucidate the seasonal variations in fine-particle composition and secondary aerosol formation, an Aerodyne quadrupole aerosol chemical speciation monitor (Q-ACSM), combined with other online instruments, was used to characterize the sub-micrometer particulate matter (diameter < 1 µ m, PM1) in Beijing during summer and winter 2015. Our results suggest that photochemical oxidation was the major pathway for sulfate formation during summer, whereas aqueous-phase reaction became an important process for sulfate formation during winter. High concentrations of nitrate (17 % of the PM1 mass) were found during winter, explained by enhanced gas-to-particle partitioning at low temperature, while high nitrate concentrations (19 %) were also observed under the conditions of high relative humidity (RH) during summer, likely due to the hydrophilic property of NH4NO3 and hydrolysis of N2O5. As for organic aerosol (OA) sources, secondary OA (SOA) dominated the OA mass (74 %) during summer, while the SOA contribution decreased to 39 % during winter due to enhanced primary emissions in the heating season. In terms of the SOA formation, photochemical oxidation perhaps played an important role for summertime oxygenated OA (OOA) formation and less-oxidized wintertime OOA (LO-OOA) formation. The wintertime more-oxidized OOA (MO-OOA) showed a good correlation with aerosol liquid water content (ALWC), indicating a more important contribution of aqueous-phase processing over photochemical production to MO-OOA. Meanwhile, the dependence of LO-OOA and the mass ratio of LO-OOA to MO-OOA on atmospheric oxidative tracer (i.e., Ox) both degraded when RH was greater than 60 %, suggesting that RH or aerosol liquid water may also affect LO-OOA formation. [ABSTRACT FROM AUTHOR]

Although much effort has been put into studying air pollution, our knowledge of the mechanisms of frequently occurring intense haze episodes in China is still limited. In this study, using 3 years of measurements of air pollutants at three different height levels on a 325 m Beijing meteorology tower, we found that a positive aerosol–boundary layer feedback mechanism existed at three vertical observation heights during intense haze polluted periods within the mixing layer. This feedback was characterized by a higher loading of PM 2.5 with a shallower mixing layer. Modelling results indicated that the presence of PM 2.5 within the boundary layer led to reduced surface temperature, relative humidity and mixing layer height during an intensive haze episode. Measurements showed that the aerosol–boundary layer feedback was related to the decrease in solar radiation, turbulent kinetic energy and thereby suppression of the mixing layer. The feedback mechanism can explain the rapid formation of intense haze episodes to some extent, and we suggest that the detailed feedback mechanism warrants further investigation from both model simulations and field observations. [ABSTRACT FROM AUTHOR]

Rapid sulfate formation is recognized as a key characteristic of severe winter haze in China. However, air quality models tend to underestimate sulfate formation during heavy haze periods, and heterogeneous formation pathways have been proposed as promising mechanisms to reduce gaps between observation and model simulation. In this study, we implemented a reactive SO2 uptake mechanism through the SO2+NO2 heterogeneous reactions in the Comprehensive Air Quality Model with Extensions (CAMx) to improve simulation of sulfate formation in the Yangtze River Delta (YRD) region. Parameterization of the SO2+NO2 heterogeneous reactions is based on observations in Beijing and considered both the impact of relative humidity and aerosol pH on sulfate formation. Ammonia is reported to be critical for the formation of secondary inorganic aerosols. Estimation of ammonia emissions is usually associated with large uncertainties and models tend to underestimate ammonia concentrations substantially. Sensitivity tests were conducted to evaluate the influence of the SO2+NO2 heterogeneous reactions as well as ammonia emissions on modeled sulfate concentrations during a period with several heavy haze episodes in the YRD region. Base case model results show large underestimation of sulfate concentrations by 36 % under polluted conditions in the YRD region. Adding the SO2+NO2 heterogeneous reactions or doubling ammonia emissions alone leads to slight model improvement (∼6 %) on simulated sulfate concentrations in the YRD region. However, model performance significantly improved when both the SO2+NO2 heterogeneous reactions and doubled ammonia emissions were included in the simulation: predicted sulfate concentrations during polluted periods increased from 23.1 µ g m -3 in the base scenario to 29.1 µ g m -3 (representing an increase of 26 %). Aerosol pH is crucial for the SO2+NO2 heterogeneous reactions, and our calculated aerosol pH is always acidic and increased by 0.7 with doubled ammonia emissions. Modeling results also show that this reactive SO2 uptake mechanism enhanced sulfate simulations by 1 to 5 µ g m -3 for the majority of the eastern and central parts of China, with more than 20 µ g m -3 increase in sulfate concentrations over the northeastern plain. These findings suggest that the SO2+NO2 heterogeneous reactions could be potentially important for sulfate formation in the YRD region as well as other parts of China. Further studies are needed to constrain the uncertainties associated with the parameterization of the SO2+NO2 heterogeneous reactions based on local data as well as to evaluate this mechanism in other regions. In addition, ammonia emissions were found to be a key driving variable of the spatial patterns of sulfate enhancement due to the new pathway. Substantial efforts are needed to improve the accuracy of the ammonia emission inventory. [ABSTRACT FROM AUTHOR]

In the summer of 2017, heavy ozone pollution swamped most of the North China Plain (NCP), with the maximum regional average of daily maximum 8 h ozone concentration (MDA8) reaching almost 120 ppbv. In light of the continuing reduction of anthropogenic emissions in China, the underlying mechanisms for the occurrences of these regional extreme ozone episodes are elucidated from two perspectives: meteorology and biogenic emissions. The significant positive correlation between MDA8 ozone and temperature, which is amplified during heat waves concomitant with stagnant air and no precipitation, supports the crucial role of meteorology in driving high ozone concentrations. We also find that biogenic emissions are enhanced due to factors previously not considered. During the heavy ozone pollution episodes in June 2017, biogenic emissions driven by high vapor pressure deficit (VPD), land cover change and urban landscape yield an extra mean MDA8 ozone of 3.08, 2.79 and 4.74 ppbv, respectively, over the NCP, which together contribute as much to MDA8 ozone as biogenic emissions simulated using the land cover of 2003 and ignoring VPD and urban landscape. In Beijing, the biogenic emission increase due to urban landscape has a comparable effect on MDA8 ozone to the combined effect of high VPD and land cover change between 2003 and 2016. In light of the large effect of urban landscape on biogenic emission and the subsequent ozone formation, the types of trees may be cautiously selected to take into account of the biogenic volatile organic compound (BVOC) emission during the afforestation of cities. This study highlights the vital contributions of heat waves, land cover change and urbanization to the occurrence of extreme ozone episodes, with significant implications for ozone pollution control in a future when heat wave frequency and intensity are projected to increase under global warming. [ABSTRACT FROM AUTHOR]

The successful bid for the 2022 Winter Olympics (Beijing 2022, officially known as the XXIV Olympic Winter Games) has greatly stimulated Chinese enthusiasm towards winter sports participation. Consequently, the Chinese ski industry is rapidly booming due to enormous market demand and government support. However, investing in ski areas in unreasonable locations will cause problems from an economic perspective (in terms of operation and management) as well as geographical concerns (such as environmental degradation). Therefore, evaluating the suitability of a ski area based on scientific metrics has become a prerequisite for the sustainable development of the ski industry. In this study, we evaluate the locational suitability of ski areas in China by integrating their natural and socioeconomic conditions using a linearly weighted method based on geographic information system (GIS) spatial analysis combined with remote sensing, online, and field survey data. The key indexes for evaluating natural suitability include snow cover, air temperature, topographic conditions, water resources, and vegetation, whereas socioeconomic suitability is evaluated based on economic conditions, accessibility of transportation, distance to a tourist attraction, and distance to a city. As such, metrics ranging from 0 to 1 considering both natural and socioeconomic conditions are used to define a suitability threshold for each candidate region for ski area development. A ski area is considered to be a dismal prospect when the locational integrated index is less than 0.5. The results show that 84 % of existing ski areas are located in areas with an integrated index greater than 0.5. Finally, corresponding development strategies for decision-makers are proposed based on the multicriteria metrics, which will be extended to incorporate potential influences from future climate change and socioeconomic development. However, the snowmaking model with local data should to be used to further analyze the suitability for a specific ski area. [ABSTRACT FROM AUTHOR]

Rapid economic growth in China over the past 30 years has resulted in significant increases in the concentrations of small particulates (PM 2.5) over the city of Beijing. In addition to health problems, high aerosol loading can impact visibility and thus reduce photolysis rates over the city, leading to potential implications for photochemistry. Photolysis rates are highly sensitive not only to the vertical distribution of aerosols but also to their composition, as this can impact how the incoming solar radiation is scattered or absorbed. This study, for the first time, uses aerosol composition measurements and lidar optical depth to drive the Fast-JX photolysis scheme and quantify the photochemical impacts of different aerosol species during the Air Pollution and Human Health (APHH) measurement campaigns in Beijing in November–December 2016 and May–June 2017. This work demonstrates that severe haze pollution events (PM 2.5 > 75 µg m -3) occur during both winter and summer, leading to reductions in O3 photolysis rates of 27 %–34 % (greatest in winter) and reductions in NO2 photolysis of 40 %–66 % (greatest in summer) at the surface. It also shows that in spite of much lower PM 2.5 concentrations in the summer months, the absolute changes in photolysis rates are larger for both O3 and NO2. In the winter, absorbing species such as black carbon dominate the photolysis response to aerosols, leading to mean reductions in J [O 1 D] and J [ NO2 ] in the lowest 1 km of 24 % and 23 %, respectively. In contrast, in the summer, scattering aerosol such as organic matter dominate the response, leading to mean decreases of 2 %–3 % at the surface and increases of 8 %–10 % at higher altitudes (3–4 km). During these haze events in both campaigns, the influence of aerosol on photolysis rates dominates over that from clouds. These large impacts on photochemistry can have significant implications for concentrations of important atmospheric oxidants such as the hydroxyl radical. Idealized photochemical box model studies show that such large impacts on photochemistry could lead to a 12 % reduction in surface O3 (3 % for OH) due to haze pollution. This highlights that PM 2.5 mitigation strategies could have important implications for the oxidation capacity of the atmosphere both at the surface and in the free troposphere. [ABSTRACT FROM AUTHOR]

As a result of partial specular reflection from the atmospheric stable layer, the radar tropopause (RT) can simply and directly be detected by VHF radars with vertical incidence. Here, the Beijing mesosphere–stratosphere–troposphere (MST) radar measurements are used to investigate the structure and the variabilities in the tropopause in Xianghe, China, with a temporal resolution of 0.5 h from November 2011 to May 2017. The high-resolution radar-derived tropopause is compared with the thermal lapse-rate tropopause (LRT) that is defined by the World Meteorological Organization (WMO) criterion from twice-daily radiosonde soundings and with the dynamical potential vorticity tropopause (PVT) that is defined as the height of the 2 PVU (PVU – potential vorticity units; 1 PVU = 106 m 2 s -1 K kg -1) surface. We only consider tropopauses below 16 km in this study because of limitations with the radar system. During all the seasons, the RT and the LRT in altitude agree well with each other, with a correlation coefficient of ≥0.74. Statistically, weaker (higher) tropopause sharpness seems to contribute to larger (smaller) difference between the RT and the LRT in altitude. The RT agrees well with the PVT in altitude during winter and spring, with a correlation coefficient of ≥0.72 , while the correlation coefficient in summer is only 0.33. As expected, the monthly mean RT and LRT height both show seasonal variations. Lomb–Scargle periodograms show that the tropopause exhibits obvious diurnal variation throughout the seasons, whereas the semidiurnal oscillations are rare and are occasionally observed during summer and later spring. Our study shows the potential of the Beijing MST radar to determine the tropopause height as well as present its diurnal oscillations. [ABSTRACT FROM AUTHOR]

On-road vehicle emissions are a major contributor to elevated air pollution levels in populous metropolitan areas. We developed a link-level emissions inventory of vehicular pollutants, called EMBEV-Link (Link-level Emission factor Model for the BEijing Vehicle fleet), based on multiple datasets extracted from the extensive road traffic monitoring network that covers the entire municipality of Beijing, China (16 400 km 2). We employed the EMBEV-Link model under various traffic scenarios to capture the significant variability in vehicle emissions, temporally and spatially, due to the real-world traffic dynamics and the traffic restrictions implemented by the local government. The results revealed high carbon monoxide (CO) and total hydrocarbon (THC) emissions in the urban area (i.e., within the Fifth Ring Road) and during rush hours, both associated with the passenger vehicle traffic. By contrast, considerable fractions of nitrogen oxides (NOx), fine particulate matter (PM 2.5) and black carbon (BC) emissions were present beyond the urban area, as heavy-duty trucks (HDTs) were not allowed to drive through the urban area during daytime. The EMBEV-Link model indicates that nonlocal HDTs could account for 29 % and 38 % of estimated total on-road emissions of NOx and PM 2.5 , which were ignored in previous conventional emission inventories. We further combined the EMBEV-Link emission inventory and a computationally efficient dispersion model, RapidAir®, to simulate vehicular NOx concentrations at fine resolutions (10 m × 10 m in the entire municipality and 1 m × 1 m in the hotspots). The simulated results indicated a close agreement with ground observations and captured sharp concentration gradients from line sources to ambient areas. During the nighttime when the HDT traffic restrictions are lifted, HDTs could be responsible for approximately 10 µ g m -3 of NOx in the urban area. The uncertainties of conventional top-down allocation methods, which were widely used to enhance the spatial resolution of vehicle emissions, are also discussed by comparison with the EMBEV-Link emission inventory. [ABSTRACT FROM AUTHOR]

Ambient particulate matter (PM) can contain a mix of different toxic species derived from a wide variety of sources. This study quantifies the diurnal variation and nocturnal abundance of 16 polycyclic aromatic hydrocarbons (PAHs), 10 oxygenated PAHs (OPAHs) and 9 nitrated PAHs (NPAHs) in ambient PM in central Beijing during winter. Target compounds were identified and quantified using gas chromatography–time-of-flight mass spectrometry (GC-Q-ToF-MS). The total concentration of PAHs varied between 18 and 297 ng m -3 over 3 h daytime filter samples and from 23 to 165 ng m -3 in 15 h night-time samples. The total concentrations of PAHs over 24 h varied between 37 and 180 ng m -3 (mean: 97±43 ng m -3). The total daytime concentrations during high particulate loading conditions for PAHs, OPAHs and NPAHs were 224, 54 and 2.3 ng m -3 , respectively. The most abundant PAHs were fluoranthene (33 ng m -3), chrysene (27 ng m -3), pyrene (27 ng m -3), benzo[a]pyrene (27 ng m -3), benzo[b]fluoranthene (25 ng m -3), benzo[a]anthracene (20 ng m -3) and phenanthrene (18 ng m -3). The most abundant OPAHs were 9,10-anthraquinone (18 ng m -3), 1,8-naphthalic anhydride (14 ng m -3) and 9-fluorenone (12 ng m -3), and the three most abundant NPAHs were 9-nitroanthracene (0.84 ng m -3), 3-nitrofluoranthene (0.78 ng m -3) and 3-nitrodibenzofuran (0.45 ng m -3). ∑ PAHs and ∑ OPAHs showed a strong positive correlation with the gas-phase abundance of NO, CO, SO2 and HONO, indicating that PAHs and OPAHs can be associated with both local and regional emissions. Diagnostic ratios suggested emissions from traffic road and coal combustion were the predominant sources of PAHs in Beijing and also revealed the main source of NPAHs to be secondary photochemical formation rather than primary emissions. PM2.5 and NPAHs showed a strong correlation with gas-phase HONO. 9-Nitroanthracene appeared to undergo a photodegradation during the daytime and showed a strong positive correlation with ambient HONO (R=0.90 , P<0.001). The lifetime excess lung cancer risk for those species that have available toxicological data (16 PAHs, 1 OPAH and 6 NPAHs) was calculated to be in the range 10 -5 to 10 -3 (risk per million people ranges from 26 to 2053 cases per year). [ABSTRACT FROM AUTHOR]

Atmospheric aerosols scatter or absorb a fraction of the incoming solar radiation to cool or warm the atmosphere, decreasing surface temperature and altering atmospheric stability to further affect the dispersion of air pollutants in the planetary boundary layer (PBL). In the present study, simulations during a persistent and heavy haze pollution episode from 5 December 2015 to 4 January 2016 in the North China Plain (NCP) were performed using the Weather Research and Forecasting model with Chemistry (WRF-Chem) to comprehensively quantify contributions of aerosol shortwave radiative feedback (ARF) to near-surface (around 15 m above the ground surface) PM 2.5 mass concentrations. The WRF-Chem model generally performs well in simulating the temporal variations and spatial distributions of air pollutants concentrations compared to observations at ambient monitoring sites in the NCP, and the simulated diurnal variations of aerosol species are also consistent with the measurements in Beijing. Additionally, the model simulates the aerosol radiative properties, the downward shortwave flux, and the PBL height against observations in the NCP well. During the episode, ARF deteriorates the haze pollution, increasing the near-surface PM 2.5 concentrations in the NCP by 10.2 µ g m -3 or with a contribution of 7.8 % on average. Sensitivity studies have revealed that high loadings of PM 2.5 attenuate the incoming solar radiation reaching the surface to cool the low-level atmosphere, suppressing the development of the PBL, decreasing the surface wind speed, further hindering the PM 2.5 dispersion, and consequently exacerbating the haze pollution in the NCP. Furthermore, when the near-surface PM 2.5 mass concentration increases from around 50 to several hundred µ g m -3 , ARF contributes to the near-surface PM 2.5 by more than 20 % during daytime in the NCP, substantially aggravating the heavy haze formation. However, when the near-surface PM 2.5 concentration is less than around 50 µ g m -3 , ARF generally reduces the near-surface PM 2.5 concentration due to the consequent perturbation of atmospheric dynamic fields. [ABSTRACT FROM AUTHOR]

Aerosol acidity plays a key role in secondary aerosol formation. The high-temporal-resolution PM 2.5 pH and size-resolved aerosol pH in Beijing were calculated with ISORROPIA II. In 2016–2017, the mean PM 2.5 pH (at relative humidity (RH) > 30 %) over four seasons was 4.5±0.7 (winter) > 4.4±1.2 (spring) > 4.3±0.8 (autumn) > 3.8±1.2 (summer), showing moderate acidity. In coarse-mode aerosols, Ca2+ played an important role in aerosol pH. Under heavily polluted conditions, more secondary ions accumulated in the coarse mode, leading to the acidity of the coarse-mode aerosols shifting from neutral to weakly acidic. Sensitivity tests also demonstrated the significant contribution of crustal ions to PM 2.5 pH. In the North China Plain (NCP), the common driving factors affecting PM 2.5 pH variation in all four seasons were SO42- , TNH3 (total ammonium (gas + aerosol)), and temperature, while unique factors were Ca2+ in spring and RH in summer. The decreasing SO42- and increasing NO3- mass fractions in PM 2.5 as well as excessive NH3 in the atmosphere in the NCP in recent years are the reasons why aerosol acidity in China is lower than that in Europe and the United States. The nonlinear relationship between PM 2.5 pH and TNH3 indicated that although NH3 in the NCP was abundant, the PM 2.5 pH was still acidic because of the thermodynamic equilibrium between NH4+ and NH3. To reduce nitrate by controlling ammonia, the amount of ammonia must be greatly reduced below excessive quantities. [ABSTRACT FROM AUTHOR]

Ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) observation was carried out from November 2016 to February 2017 in Beijing, China, to measure the O4 absorptions in UV and visible bands and further to illustrate its relationship with aerosol optical properties (AOPs) under different weather types. According to relative humidity, visibility, and PM 2.5 , we classified the observation periods into clear, light-haze, haze, heavy-haze, fog, and rainy weather conditions. There are obvious differences for measured AOPs under different weather conditions, especially scattering coefficient (σsca) and absorption coefficient (σsca). It was also found that both the O4 differential slant column densities (DSCDs) at the UV and visible bands varied in the order of clear days > light-haze days > haze days > heavy-haze days > fog days. The correlation coefficients (R2) between O4 DSCDs at 360.8 and 477.1 nm mainly varied in the order of clear days > light-haze days > haze days > heavy-haze days. Based on the statistics of O4 DSCDs at an elevation angle 1 ∘ with the corresponding linear regression between UV and visible bands of segmental periods, the relationships between O4 DSCDs and AOPs were established. It should mainly be clear or light-haze days when the correlation slope is greater than 1.0, with a correlation coefficient (R2) greater than 0.9, and O4 DSCDs mainly greater than 2.5×1043 molec. cm -2. Meanwhile, σsca and σabs are less than 45 and 12 Mm -1 , respectively. For haze or heavy-haze days, the correlation slope is less than 0.6, with an R2 less than 0.8, and O4 DSCDs mainly less than 1.3×1043 molec. cm -2 , under which σsca and σabs are mainly located at 200–900 and 20–60 Mm -1. Additionally, the determination method was well validated based on another MAX-DOAS measurement at Gucheng from 19 to 27 November 2016. For more precise and accurate inversion of AOPs, more detailed look-up tables for O4 multiple-wavelength absorptions need to be developed. Since the ground surface AOPs were determined using MAX-DOAS observation at a 1 ∘ elevation in this study, we hope to highlight the potential of retrieved vertical spatially resolved AOPs being expected when multiple elevation angles of MAX-DOAS observation are used together. [ABSTRACT FROM AUTHOR]

Nitro-aromatic compounds (NACs), as important contributors to the light absorption by brown carbon, have been widely observed in various ambient atmospheres; however, their formation in the urban atmosphere was little studied. In this work, we report an intensive field study of NACs in summer 2016 at an urban Beijing site, characterized by both high- NOx and anthropogenic VOC dominated conditions. We investigated the factors that influence NAC formation (e.g., NO2 , VOC precursors, RH and photolysis) through quantification of eight NACs, along with major components in fine particulate matter, selected volatile organic compounds, and gases. The average total concentration of the quantified NACs was 6.63 ng m -3 , higher than those reported in other summertime studies (0.14–6.44 ng m -3). 4-Nitrophenol (4NP, 32.4 %) and 4-nitrocatechol (4NC, 28.5 %) were the top two most abundant NACs, followed by methyl-nitrocatechol (MNC), methyl-nitrophenol (MNP), and dimethyl-nitrophenol (DMNP). The oxidation of toluene and benzene in the presence of NOx was found to be a more dominant source of NACs than primary biomass burning emissions. The NO2 concentration level was found to be an important factor influencing the secondary formation of NACs. A transition from low- to high- NOx regimes coincided with a shift from organic- to inorganic-dominated oxidation products. The transition thresholds were NO2∼20 ppb for daytime and NO2∼25 ppb for nighttime conditions. Under low- NOx conditions, NACs increased with NO2 , while the NO3- concentrations and (NO3-)/NACs ratios were lower, implying organic-dominated products. Under high- NOx conditions, NAC concentrations did not further increase with NO2 , while the NO3- concentrations and (NO3-)/NACs ratios showed increasing trends, signaling a shift from organic- to inorganic-dominated products. Nighttime enhancements were observed for 3M4NC and 4M5NC, while daytime enhancements were noted for 4NP, 2M4NP, and DMNP, indicating different formation pathways for these two groups of NACs. Our analysis suggested that the aqueous-phase oxidation was likely the major formation pathway of 4M5NC and 3M5NC, while photo-oxidation of toluene and benzene in the presence of NO2 could be more important for the formation of nitrophenol and its derivatives. Using the (3M4NC + 4M5NC) / 4NP ratios as an indicator of the relative contribution of aqueous-phase and gas-phase oxidation pathways to NAC formation, we observed that the relative contribution of aqueous-phase pathways increased at elevated ambient RH and remained constant at RH > 30 %. We also found that the concentrations of VOC precursors (e.g., toluene and benzene) and aerosol surface area acted as important factors in promoting NAC formation, and photolysis as an important loss pathway for nitrophenols. [ABSTRACT FROM AUTHOR]

The implementation of the Air Pollution Prevention and Control Action Plan in China since 2013 has profoundly altered the ambient pollutants in the Beijing–Tianjin–Hebei (BTH) region. Here we show observations of substantially increased O3 concentrations (about 30 %) and a remarkable increase in the ratio of organic carbon (OC) to elemental carbon (EC) in BTH during the autumn from 2013 to 2015, revealing an enhancement in atmospheric oxidizing capacity (AOC) and secondary organic aerosol (SOA) formation. To explore the impacts of increasing AOC on the SOA formation, a severe air pollution episode from 3 to 8 October 2015 with high O3 and PM 2.5 concentrations is simulated using the WRF-Chem model. The model performs reasonably well in simulating the spatial distributions of PM 2.5 and O3 concentrations over BTH and the temporal variations in PM 2.5 , O3 , NO2 , OC, and EC concentrations in Beijing compared to measurements. Sensitivity studies show that the change in AOC substantially influences the SOA formation in BTH. A sensitivity case characterized by a 31 % O3 decrease (or 36 % OH decrease) reduces the SOA level by about 30 % and the SOA fraction in total organic aerosol by 17 % (from 0.52 to 0.43, dimensionless). Spatially, the SOA decrease caused by reduced AOC is ubiquitous in BTH, but the spatial relationship between SOA concentrations and the AOC is dependent on the SOA precursor distribution. Studies on SOA formation pathways further show that when the AOC is reduced, the SOA from oxidation and partitioning of semivolatile primary organic aerosol (POA) and co-emitted intermediate volatile organic compounds (IVOCs) decreases remarkably, followed by those from anthropogenic and biogenic volatile organic compounds (VOCs). Meanwhile, the SOA decrease in the irreversible uptake of glyoxal and methylglyoxal on the aerosol surfaces is negligible. [ABSTRACT FROM AUTHOR]

Comprehensive chlorine heterogeneous chemistry is incorporated into the Community Multiscale Air Quality (CMAQ) model to evaluate the impact of chlorine-related heterogeneous reaction on diurnal and nocturnal nitrate formation and quantify the nitrate formation from gas-to-particle partitioning of HNO3 and from different heterogeneous pathways. The results show that these heterogeneous reactions increase the atmospheric Cl2 and ClNO2 level (∼100 %), which further affects the nitrate formation. Sensitivity analyses of uptake coefficients show that the empirical uptake coefficient for the O3 heterogeneous reaction with chlorinated particles may lead to the large uncertainties in the predicted Cl2 and nitrate concentrations. The N2O5 uptake coefficient with particulate Cl- concentration dependence performs better in capturing the concentration of ClNO2 and nocturnal nitrate concentration. The reaction of OH and NO2 in the daytime increases the nitrate by ∼15 % when the heterogeneous chlorine chemistry is incorporated, resulting in more nitrate formation from HNO3 gas-to-particle partitioning. By contrast, the contribution of the heterogeneous reaction of N2O5 to nitrate concentrations decreases by about 27 % in the nighttime, when its reactions with chlorinated particles are considered. However, the generated gas-phase ClNO2 from the heterogeneous reaction of N2O5 and chlorine-containing particles further reacts with the particle surface to increase the nitrate by 6 %. In general, this study highlights the potential of significant underestimation of daytime concentrations and overestimation of nighttime nitrate concentrations for chemical transport models without proper chlorine chemistry in the gas and particle phases. [ABSTRACT FROM AUTHOR]

Improving the accuracy of the anthropogenic volatile organic compound (VOC) emission inventory is essential for reducing air pollution. In this study, we established an emission inventory of anthropogenic VOCs in the Beijing–Tianjin–Hebei (BTH) region of China for 2015 based on the emission factor (EF) method. Online ambient VOC observations were conducted in one urban area of Beijing in January, April, July, and October, which, respectively, represented winter, spring, summer, and autumn in 2015. Furthermore, the developed emission inventory was evaluated by a comprehensive verification system based on the measurements and satellite retrieval results. Firstly, emissions of the individual species of the emission inventory were evaluated according to the ambient measurements and emission ratios versus carbon monoxide (CO). Secondly, the source structure of the emission inventory was evaluated using source appointment with the Positive Matrix Factorization (PMF) model. Thirdly, the spatial and temporal distribution of the developed emission inventory was evaluated by a satellite-derived emission inventory. According to the results of the emission inventory, the total anthropogenic VOC emissions in the BTH region were 3277.66 Gg in 2015. Online measurements showed that the average mixing ratio of VOCs in Beijing was approximately 49.94 ppbv in 2015, ranging from 10.67 to 245.54 ppbv. The annual emissions for 51 of 56 kinds of non-methane hydrocarbon species derived from the measurements agreed within ±100 % with the results of the emission inventory. Based on the PMF results and the emission inventory, it is evident that vehicle-related emissions dominate the composition of anthropogenic VOCs in Beijing. The spatial correlation between the emission inventory and satellite inversion result was significant (p<0.01) with a correlation coefficient of 0.75. However, there were discrepancies between the relative contributions of fuel combustion, emissions of oxygenated VOCs (OVOCs), and halocarbons from the measurements and inventory. To obtain a more accurate emission inventory, we propose the investigation of the household coal consumption, the adjustment of EFs based on the latest pollution control policies, and the verification of the source profiles of OVOCs and halocarbons. [ABSTRACT FROM AUTHOR]

The detailed formation mechanism of an increased number of haze events in China is still not very clear. Here, we found that reduced surface visibility from 1980 to 2010 and an increase in satellite-derived columnar concentrations of inorganic precursors from 2002 to 2012 are connected with each other. Typically, higher inorganic mass fractions lead to increased aerosol water uptake and light-scattering ability in elevated relative humidity. Satellite observation of aerosol precursors of NO2 and SO2 showed increased concentrations during the study period. Our in situ measurement of aerosol chemical composition in Beijing also confirmed increased contribution of inorganic aerosol fraction as a function of the increased particle pollution level. Our investigations demonstrate that the increased inorganic fraction in the aerosol particles is a key component in the frequently occurring haze days during the study period, and particularly the reduction of nitrate, sulfate and their precursor gases would contribute towards better visibility in China. [ABSTRACT FROM AUTHOR]

Extensive fossil fuel combustion in rapidly developing cities severely affects air quality and public health. We report observational evidence of decadal changes in the efficiency and cleanness of bulk combustion over large cities in mainland China. In order to estimate the trends in enhancement ratios of CO and SO2 to NO2 (ΔCO/ΔNO2 and ΔSO2/ΔNO2) and infer emergent bulk combustion properties over these cities, we combine air quality retrievals from widely used satellite instruments across 2005–2014. We present results for four Chinese cities (Shenyang, Beijing, Shanghai, and Shenzhen) representing four levels of urban development. Our results show a robust coherent progression of declining to growing ΔCO/ΔNO2 relative to 2005 (-5.4±0.7 to +8.3±3.1% yr -1) and slowly declining ΔSO2/ΔNO2 (-6.0±1.0 to -3.4±1.0 % yr -1) across the four cities. The coherent progression we find is not evident in the trends of emission ratios reported in Representative Concentration Pathway (RCP8.5) inventory. This progression is likely due to a shift towards cleaner combustion from industrial and residential sectors in Shanghai and Shenzhen that is not yet seen in Shenyang and Beijing. This overall trend is presently obfuscated by China's still relatively higher dependence on coal. Such progression is well-correlated with economic development and traces a common emission pathway that resembles evolution of air pollution in more developed cities. Our results highlight the utility of augmenting observing and modeling capabilities by exploiting enhancement ratios in constraining the time variation in emission ratios in current inventories. As cities and/or countries continue to socioeconomically develop, the ability to monitor combustion efficiency and effectiveness of pollution control becomes increasingly important in assessing sustainable control strategies. [ABSTRACT FROM AUTHOR]