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A general feature in the diurnal cycle of atmospheric ammonia (NH3) concentrations is a morning spike that typically occurs around 07:00 to 10:00 (LST). Current hypotheses to explain this morning’s NH3increase remain elusive, and there is still no consensus whether traffic emissions are among the major sources of urban NH3. Here, we confirmed that the NH3morning pulse in urban Beijing is a universal feature, with an annual occurrence frequency of 73.0% and a rapid growth rate (>20%) in winter. The stable nitrogen isotopic composition of NH3(δ15N–NH3) in winter also exhibited a significant diurnal variation with an obvious morning peak at 07:00 to 10:00 (−18.6‰, mass-weighted mean), higher than other times of the day (−26.3‰). This diurnal pattern suggests that a large fraction of NH3in the morning originated from nonagricultural sources, for example, power plants, vehicles, and coal combustion that tend to have higher δ15N–NH3emission signatures relative to agricultural emissions. In particular, the contribution from vehicular emissions increased from 18% (00:00 to 07:00) to 40% (07:00 to 10:00), while the contribution of fertilizer sources to NH3was reduced from 15.8% at 00:00 to 07:00 to 5.2% at 07:00 to 10:00. We concluded that NH3concentrations in winter mornings in urban Beijing were indeed enhanced by vehicle emissions, which should be considered in air pollution regulations.

Multiaxis differential absorption spectroscopy (MAX-DOAS) is a newly developed advanced vertical profile detection method, but the vertical nitrogen dioxide (NO2) profiles measured by MAX-DOAS have not yet been fully verified. In this study, we perform MAX-DOAS and tower gradient observations to simultaneously acquire tropospheric NO2observations in the Beijing urban area from 1 April to 31 May 2019. The average values of the tropospheric NO2vertical column densities measured by MAX-DOAS and the tropospheric monitoring instrument are 15.8 × 1015and 12.4 × 1015molecules cm−2, respectively, and the correlation coefficient Rreaches 0.87. The MAX-DOAS measurements are highly consistent with the tower-based in situ measurements, and the correlation coefficients R from the ground to the upper air are 0.89 (60 m), 0.87 (160 m), and 0.76 (280 m). MAX-DOAS accurately measures the trend of NO2vertical profile changes, although a large underestimation occurs by a factor of two. By analyzing the NO2vertical profile, the NO2concentration reveals an exponential decrease with height. The NO2vertical profile also coincides with the evolution of the boundary layer height. The study shows that the NO2over Beijing mainly originates from local sources and occurs in the boundary layer, and its vertical evolution pattern has an important guiding significance to better understand nitrate production and ozone pollution.

The vertical observation of volatile organic compounds (VOCs) is an important means to clarify the mechanisms of ozone formation. To explore the vertical evolution of VOCs in summer, a field campaign using a tethered balloon during summer photochemical pollution was conducted in Shijiazhuang from 8 June to 3 July 2019. A total of 192 samples were collected, 23 vertical profiles were obtained, and the concentrations of 87 VOCs were measured. The range of the total VOC concentration was 41–48 ppbv below 600 m. It then slightly increased above 600 m, and rose to 58 ± 52 ppbv at 1000 m. The proportion of alkanes increased with height, while the proportions of alkenes, halohydrocarbons and acetylene decreased. The proportion of aromatics remained almost unchanged. A comparison with the results of a winter field campaign during 8–16 January 2019 showed that the concentrations of all VOCs in winter except for halohydrocarbons were more than twice those in summer. Alkanes accounted for the same proportion in winter and summer. Alkenes, aromatics, and acetylene accounted for higher proportions in winter, while halohydrocarbons accounted for a higher proportion in summer. There were five VOC sources in the vertical direction. The proportions of gasoline vehicular emissions + industrial sources and coal burning were higher in winter. The proportions of biogenic sources + long-range transport, solvent usage, and diesel vehicular emissions were higher in summer. From the surface to 1000 m, the proportion of gasoline vehicular emissions + industrial sources gradually increased.

The concentration of fine particulate matter (PM2.5) across China has decreased by 30–50% over the period 2013–2018 due to stringent emission controls. However, the nitrate component of PM2.5has not responded effectively to decreasing emissions of nitrogen oxides and has actually increased during winter haze pollution events in the North China Plain. Here, we show that the GEOS-Chem atmospheric chemistry model successfully simulates the nitrate concentrations and trends. We find that winter mean nitrate would have increased over 2013–2018 were it not for favourable meteorology. The principal cause of this nitrate increase is weaker deposition. The fraction of total inorganic nitrate as particulate nitrate instead of gaseous nitric acid over the North China Plain in winter increased from 90% in 2013 to 98% in 2017, as emissions of nitrogen oxides and sulfur dioxide decreased while ammonia emissions remained high. This small increase in the particulate fraction greatly slows down deposition of total inorganic nitrate and hence drives the particulate nitrate increase. Our results suggest that decreasing ammonia emissions would decrease particulate nitrate by driving faster deposition of total inorganic nitrate. Decreasing nitrogen oxide emissions is less effective because it drives faster oxidation of nitrogen oxides and slower deposition of total inorganic nitrate.

Exploring the vertical variation in volatile organic compounds (VOCs) in background regions can provide information on the spatial distribution of pollutants, providing a scientific basis for atmospheric pollution prevention and control strategies. From 15 August to 5 September 2023, at the Southeast Tibet Mountain Comprehensive Environmental Observation Station (SETS), a tethered balloon was used to sample VOCs every 100 m from the ground to 1000 m. A total of 403 air bag samples were collected, and 39 vertical profiles of VOCs were obtained. Ninety-two VOC species were detected. The VOC concentration at the SETS did not change significantly vertically, and the average VOC concentration was 11.1 ± 2.4 ppbv. The main components were alkanes (51.4 %), alkenes (18.7 %), and halohydrocarbons (18.1 %). There was no obvious diurnal change in VOCs and no significant difference between the different layers. When the surface VOC concentration was less than 10 ppbv, the concentrations, components, and sources of VOCs were evenly distributed vertically, and the main sources of VOCs at different heights were vehicle exhaust and background. When the surface VOC concentration exceeded 10 ppbv, the VOC concentration gradually decreased with height. The proportion of alkanes in surface VOCs increased, and the source was mainly vehicle exhaust. This study confirmed that VOCs are vertically homogeneous in the background of the Tibetan Plateau, emphasizing the importance of vehicle emissions as a potential source of VOCs.

A full understanding of the sources of atmospheric nitrous acid (HONO) in the polluted urban atmosphere remains a challenge. In this study, ambient HONO and relevant species were measured during January 2019 at an urban site in Beijing, China, and a budget analysis of HONO was conducted using a box model combined with field observations. Large nighttime “missing sources” of HONO were identified on heavily polluted days based on traditional sources, which had a significant correlation with the relative humidity, ammonia (NH3), and aerosol surface area, and the promotional effect of NH3for nitrogen dioxide (NO2) uptake on the wet aerosol surface was discussed. Then, an updated parameterization scheme for quantifying the enhanced heterogeneous reactions of NO2on aerosol surfaces is proposed, and the missing nighttime sources of HONO could be substantially compensated after the new scheme was incorporated. Further evaluation on the contributions of HONO to hydroxyl radicals was conducted, and the authors found that the photolysis of HONO played a dominant role in the primary OH production on the polluted days (78%–90%). The study reveals great potential of an NH3-enhanced uptake coefficient of NO2on the aerosol surface in the nocturnal HONO budget, and highlights the significance of HONO in the strong atmospheric oxidation capability during episodes with a heavily polluted atmosphere.

Photochemical smog characterized by high concentrations of ozone (O3) is a serious air pollution issue in the North China Plain (NCP) region, especially in summer and autumn. For this study, measurements of O3, nitrogen oxides (NOx), volatile organic compounds (VOCs), carbon monoxide (CO), nitrous acid (HONO), and a number of key physical parameters were taken at a suburban site, Xianghe, in the NCP region during the summer of 2018 in order to better understand the photochemical processes leading to O3formation and find an optimal way to control O3pollution. Here, the radical chemistry and O3photochemical budget based on measurement data from 1–23 July using a chemical box model is investigated. The daytime (0600–1800 LST) average production rate of the primary radicals referred to as ROx(OH + HO2+ RO2) is 3.9 ppbv h−1. HONO photolysis is the largest primary ROxsource (41%). Reaction of NO2+ OH is the largest contributor to radical termination (41%), followed by reactions of RO2+ NO2(26%). The average diurnal maximum O3production and loss rates are 32.9 ppbv h−1and 4.3 ppbv h−1, respectively. Sensitivity tests without the HONO constraint lead to decreases in daytime average primary ROxproduction by 55% and O3photochemical production by 42%, highlighting the importance of accurate HONO measurements when quantifying the ROxbudget and O3photochemical production. Considering heterogeneous reactions of trace gases and radicals on aerosols, aerosol uptake of HO2contributes 11% to ROxsink, and the daytime average O3photochemical production decreases by 14%. The O3-NOx-VOCs sensitivity shows that the O3production at Xianghe during the investigation period is mainly controlled by VOCs.

Industrial pollution has a significant effect on aerosol properties in Changsha City, a typical city of central China. Therefore, year-round measurements of aerosol optical, radiative and chemical properties from 2012 to 2014 at an urban site in Changsha were analyzed. During the observation period, the energy structure was continuously optimized, which was characterized by the reduction of coal combustion. The aerosol properties have obvious seasonal variations. The seasonal average aerosol optical depth (AOD) at 500 nm ranged from 0.49 to 1.00, single scattering albedo (SSA) ranged from 0.93 to 0.97, and aerosol radiative forcing at the top of the atmosphere (TOA) ranged from −24.0 to 3.8 W m−2. The chemical components also showed seasonal variations. Meanwhile, the scattering aerosol, such as organic carbon, SO42−, NO3−, and NH4+showed a decrease, and elemental carbon increased. Compared with observation in winter 2012, AOD and TOA decreased by 0.14 and −1.49 W m−2in winter 2014. The scattering components, SO42−, NO3−and NH4+, decreased by 12.8 µg m−3(56.8%), 9.2 µg m−3(48.8%) and 6.4 µg m−3(45.2%), respectively. The atmospheric visibility and pollution diffusion conditions improved. The extinction and radiative forcing of aerosol were significantly controlled by the scattering aerosol. The results indicate that Changsha is an industrial city with strong scattering aerosol. The energy structure optimization had a marked effect on controlling pollution, especially in winter (strong scattering aerosol).

Gaseous nitrous acid (HONO) is a crucial precursor of the hydroxyl (OH) radical, which is a “detergent” in the atmosphere. Nowadays, HONO formation mechanisms at polluted urban areas are controversial, which restricts the understanding of atmospheric oxidative capacity and radical cycling. Herein, multiday vertical observation of HONO and NOxwas simultaneously performed at three heights at the urban area of Beijing for the first time. The vertical distribution of HONO was often unexpected, and it had the highest HONO concentration at 120 m, followed by those at 8 and 240 m. 0D box model simulations suggest that ground and aerosol surfaces might play similar roles in NO2conversion at 8 m during the whole measurement. NO2conversion on aerosol surfaces was the most important HONO source aloft during haze days. At daytime, a strong missing HONO source unexpectedly existed in the urban aloft, and it was relevant to solar radiation and consumed OH.

ABSTRACTDue to profound impact on climate and human health, air quality has attracted attention from all levels of the civil society. The key step in the provision of required tools for the society to tackle the complex air quality problem is to characterize it in a comprehensive manner with a long-term perspective. Here, we describe a continuous and comprehensive observation station and its accompanying state-of-the-art instrumentation that was established to investigate the complex urban atmospheric environment in a rapidly developing Chinese Megacity. The station, located in downtown Beijing, aims to study air quality by identifying the major atmospheric pollutants and key processes determining their formation and loss mechanisms. A few hundreds of parameters are continuously measured with the state-of-the-art instruments, including trace gas concentrations, aerosol particle size distributions, and mass concentrations, covering aerosol particle chemical composition from molecules to micrometer-sized aerosol particles. This produced long-term, comprehensive big data with around bytes per year. In this paper, we provide an overview on the facilities of the station, the instrumentation used, the workflow of continuous observations and examples of results from 2018 to 2019 and a basis for establishing a modern long-term, comprehensive atmospheric urban observation station in other megacities.

ABSTRACTExcess nitrogen deposition has significant impacts on water eutrophication, soil acidification, eleveted greenhouse gas emissions, and biodiversity loss. These impacts mostly derive from conventional manipulative experiments in the field by adding nitrogen solution directly onto grassland or forest floors. For forest ecosystems, previous field experiments have usually ignored the nitrogen cycles in the canopy, which are important in responses to airborne nitrogen input. Although whole-forest canopy nitrogen fertilization has recently been conducted to promote our understanding of nitrogen deposition processes, spraying nitrogen solution onto plants still largely ignores the dry deposition of ammonia (as well as other gaseous reactive nitrogen species). To date, there have been a limited number of field studies that have investigated the bi-directional exchange of ammonia between the atmosphere and plants, not to mention the impacts of ammonia on natural ecosystems. Due to the increasing trend of atmospheric ammonia concentrations worldwide and its dominant role in nitrogen deposition and haze pollution, the next generation of experiments should mimick nitrogen deposition on natural ecosystems by further considering the dry deposition of ammonia.

ABSTRACTOpen biomass burning (OBB) has a significant impact on the heavy haze pollution in Northeast China (NEC) in recent years, which requires the investigation of the spatiotemporal variations of OBB with different vegetation types to better monitor and control OBB in NEC. The MODIS C6 fire and land cover products, together with the emissions inventory from the Global Fire Assimilation System, were used in this study. The changes in the total number of MODIS fire points in NEC from 2003 to 2017 demonstrated a fluctuating but generally rising trend, with a peak during 2013–2017. Most fire points concentrated in two key periods, i.e. March–April (37%) and October–November (46%). The total number of crop residue burnings in March–April was basically slightly fluctuating and increased sharply from 2013, whilst the number in October–November had a fluctuating and upward trend until 2015, when a decline appeared. The amount of OBB in March–April was higher than that in October–November during 2016–17. OBB in Heilongjiang Province comprised a major proportion of all fires, which accounted for 70.7% from 2003 to 2017; however, the proportion was only 66.2% during 2013–2017. The largest proportion of all fires was in cropland (90.8%), then forest (5.3%) and grassland (3.1%). The cumulative emissions of fine particulate matter, nitrogen oxides, and ammonia from agricultural open burning in NEC reached 78.43 Gg, 24.9 Gg, and 13.7 Gg for March–April during 2013–17, respectively, which were close to those in October–November.

ABSTRACTBased on online observations of fine particulate matter (PM2.5) for five consecutive years from January 2013 to December 2017 in Beijing, combined with simultaneous measurement of gaseous precursors and meteorological parameters, the evolution and meteorological causes of fine-particle explosive growth (FPEG) events were analyzed. During the 5-year observation period, 132 FPEG events were observed and these events were further divided into three types (3-, 6-, and 9-h events) according to their evolution duration. The majority of FPEG events were observed in winter under the conditions of higher gas precursor concentrations and unfavorable meteorological conditions. The average concentration of PM2.5during winter FPEG events changed little from 2013 to 2016, whereas it decreased significantly in 2017, in accordance with the similar variation of gaseous species (SO2, NO2, and CO). In addition, the higher wind speeds and lowest relative humidity observed in 2017 were also conducive to the decrease in PM2.5. The evolutions of FPEG events and normal haze episodes were analyzed, revealing that the rate of increase in NO2was much greater than that of SO2, suggesting more of a contribution from mobile sources than stationary sources. The polarPlot results suggest that the transportation from the southeast area of Beijing plays a major role in the formation of 3-h events, whereas local emissions is the main contributory factor for 9-h events and normal haze episodes. However, further quantitative analysis regarding the contributions of these factors is still needed.

Accurate determination of the atmospheric particulate matter mass concentration and chemical composition is helpful in exploring the causes and sources of atmospheric enthalpy pollution and in evaluating the rationality of environmental air quality control strategies. Based on the sampling and chemical composition data of PM2.5in different key regions of China in the CARE-China observation network, this research analyzes the environmental air quality data released by the China National Environmental Monitoring Centre during the studied period to determine the changes in the particulate matter mass concentration in key regions and the evolution of the corresponding chemical compositions during the implementation of the Action Plan for Prevention and Control of Air Pollutionfrom 2013–2017. The results show the following. (1) The particulate matter mass concentration in China showed a significant downward trend; however, the PM2.5annual mass concentration in 64% of cities exceeds the New Chinese Ambient Air Quality Standard (CAAQS) Grade II (GB3095-2012). The region to the east of the Taihang Mountains, the Fenhe and Weihe River Plain and the Urumqi-Changji regions in Xinjiang, all have PM2.5concentration loading that is still high, and heavy haze pollution occurred frequently in the autumn and winter. (2) During the heavy pollution in the autumn and winter, the concentrations of sulfate and organic components decreased significantly. The mean SO42−concentration in PM2.5decreased by 76%, 12%, 81% and 38% in Beijing-Tianjin-Hebei (BTH), the Pearl River Delta (PRD), the Sichuan-Chongqing region (SC) and the Fenhe and Weihe River Plain, respectively. The mean organic matter (OM) concentration decreased by 70%, 44%, 48% and 31%, respectively, and the mean concentration of NH4+decreased by 68%, 1.6%, 38% and 25%, respectively. The mean elemental carbon (EC) concentration decreased by 84% and 20% in BTH and SC, respectively, and it increased by 61% and 11% in the PRD and Fenhe and Weihe River Plain, respectively. The mean concentration of mineral and unresolved chemical components (MI) dropped by 70%, 24% and 13% in BTH, the PRD and the Fenhe and Weihe River Plain, respectively. The change in the PM2.5chemical composition is consistent with the decrease of the PM2.5mass concentration. (3) In 2015, the mean OM concentration contributions to fine particles and coarse particles were 13–46% and 46–57%, respectively, and the mean MI concentration contributions to fine particles and coarse and particles were 31–60% and 39–73%, respectively; these values are lower than the 2013 values from the key regions, which is the most important factor behind the decrease of the particulate matter mass concentration. From 2013 to 2015, among the chemical components of different particle size fractions, the peak value of the coarse particle size fraction decreased significantly, and the fine particle size fractions of SO42−,NO4−,andNH4+decreased with the decrease of the particulate matter mass concentration in different particle size fractions. The fine-particle size peaks of SO42−,NO4−,andNH4+shifted from 0.65–1.1 μm to the finer size range of 0.43–0.65 μm during the same time frame.

To better investigate the characteristics and sources of trace elements (TEs) in PM2.5in urban Beijing, a 1‐year hourly observation was continuously made using an online multi‐element analyzer from 1 June 2016 to 31 May 2017. The average concentrations of 14 individual TEs ranged from 1.1 (V) to 900 ng/m3(K). The occurrence levels of most TEs of interest in Beijing were lower than those in most domestic cities, but higher than those in most foreign countries. The formation of sulfate increased with the concentrations of all studied TEs during autumn and winter. Dust, industry, biomass burning and waste incineration, vehicle emissions, coal combustion, and oil combustion were identified by the positive matrix factorization (PMF) model, which accounted for 36.3%, 10.7%, 27.1%, 13.7%, 7.6%, and 4.6%, respectively, of the total elements. All factors exhibited higher concentrations on weekends than on weekdays. Local vehicular emissions and industry contributed to the loading of TEs, but dust, biomass burning and waste incineration, coal combustion, and oil combustion from neighboring areas appeared to be dominant sources of TEs. Except for dust and industry, the four other sources of TEs were mainly located in the south and southeast areas of the sampling site. The analysis by conditional probability function and potential source contribution function showed that the distribution of the PMF sources of TEs roughly agreed with the location of the main point sources. Overall, this work provides more detailed information on the characteristics of the TEs for the scientific community and modelling work. A 1‐year hourly observation of trace elements (TEs) was continuously made using an online multi‐element analyzer in urban Beijing. The levels of most TEs of interest in Beijing were lower than those in most domestic cities of China but higher than those in most foreign countries. The formation of sulfate increased with the concentrations of all studied trace elements during autumn and winter. Six categories of sources of TEs were identified using the positive matrix factorization (PMF) model. All factors exhibited higher concentrations on weekends than on weekdays. Except for dust and industry, the four other sources of the TEs were mainly located in areas to the south and southeast of the sampling site. The analysis by conditional probability function and potential source contribution function showed that the distribution of the PMF sources of the TEs roughly agreed with the location of main point sources. The sulfur oxidation ratio increased with the concentrations of all studied trace elements during autumn and winterSix sources were identified based on a full year of hourly measurement of trace elements in PM2.5Higher concentrations of the trace element sources were observed on weekends than on weekdays

Prolactin (PRL) and its receptor, PRLR, are closely related to the occurrence and development of breast cancer. hPRL-G129R, an hPRLR antagonist, has been found to induce apoptosis in breast cancer cells via mechanisms currently unknown. Recent studies have indicated that PRLR exhibits dual functions based on its membrane/nucleus localization. In that context, we speculated whether hPRL-G129R is a dual-function antagonist. We studied the internalization of the hPRLR-G129R/PRLR complex using indirect immunofluorescence and Western blot assays. We found that hPRL-G129R not only inhibited PRLR-mediated intracellular signaling at the plasma membrane, but also blocked nuclear localization of the receptor in T-47D and MCF-7 cells in a time-dependent manner. Clone formation and transwell migration assays showed that hPRL-G129R inhibited PRL-driven proliferation and migration of tumor cells in vitro. Further, we found that increasing concentrations of hPRL-G129R inhibited the nuclear localization of PRLR and the levels of signal transducer and activator of transcription (STAT) 5 in tumor-bearing mice and hPRL-G129R also exerted an antiproliferative effect in vivo. These results indicate that hPRL-G129R is indeed a dual-function antagonist. This study lays a foundation for exploring and developing highly effective agents against the proliferation and progression of breast malignancies.

Aerosol ammonium (NH4+) can be a major component of fine particles, especially during severe haze episodes. The abatement of ammonia (NH3) emissions is important for reducing fine particles, but NH3sources remain poorly constrained and are largely unregulated in China and most other regions. This study uses stable isotopes to interpret the role NH3sources play in generating different sized NH4+aerosols in Beijing between 21 June and 4 July 2013 with fine particle concentrations of 20–242 μg/m3. The concentrations and nitrogen stable isotope composition of aerosol NH4+(δ15N‐NH4+) were both elevated during the five haze episodes that were sampled. These increases were driven by enhancements in the fine mode as opposed to substantial increases in the coarse mode aerosol. After accounting for the isotope fractionation that occurs during gas‐to‐particle partitioning (17.7‰ to 28.2‰), the “initial” (prepartitioning) δ15N‐NH3values were estimated to be −35‰ for a clean period (i.e., a nonhazy day) and ranged from −14.3‰ to −22.8‰ for hazy days. Source apportionment using the “IsoSources” isotopic mixing model indicated that the dominant contribution to NH3shifted from agricultural sources during the clean period (86%) to fossil fuel emissions (54%–81%) during hazy days and when back trajectories rotate from the northwest to the west and/or south. These results together suggest that even in summer, fossil fuel‐related sources from Beijing and the surrounding areas are the major source of NH3during haze events and that controlling these sources may be important for alleviating particulate matter pollution. Nitrogen stable isotope composition of ammonium in fine particles was higher on polluted days than during a clean periodSubstantial isotopic exchange occurred during haze episodes with excess ammoniaAgriculture and fossil fuel combustion dominate urban ammonia sources during clean and hazy days, respectively

The limited availability of ammonia (NH3) measurements is currently a barrier to understanding the vital role of NH3in secondary aerosol formation during haze pollution events and prevents a full assessment of the atmospheric deposition of reactive nitrogen. The observational gaps motivated us to design this study to investigate the spatial distributions and seasonal variations in atmospheric NH3on a national scale in China. On the basis of a 1-year observational campaign at 53 sites with uniform protocols, we confirm that abundant concentrations of NH3[1 to 23.9 μg m–3] were identified in typical agricultural regions, especially over the North China Plain (NCP). The spatial pattern of the NH3surface concentration was generally similar to those of the satellite column concentrations as well as a bottom-up agriculture NH3emission inventory. However, the observed NH3concentrations at urban and desert sites were comparable with those from agricultural sites and 2–3 times those of mountainous/forest/grassland/waterbody sites. We also found that NH3deposition fluxes at urban sites account for only half of the emissions in the NCP, suggesting the transport of urban NH3emissions to downwind areas. This finding provides policy makers with insights into the potential mitigation of nonagricultural NH3sources in developed regions.

Aerosol observational data for 2012 obtained from Dunhuang Station of CARE-China (Campaign on Atmospheric Aerosol Research Network of China) were analyzed to achieve in-depth knowledge of aerosol optical properties over Dunhuang region. The results showed that the annual average aerosol optical depth (AOD) at 500 nm was 0.32±0.06, and the Ångström exponent (α) was 0.73 ± 0.27. Aerosol optical properties revealed significant seasonal characteristics. Frequent sandstorms in MAM (March–April–May) resulted in the seasonal maximum AOD, 0.41 ± 0.04, and a relatively smaller αvalue, 0.44±0.04. The tourism seasons, JJA (June–July–August) and SON (September–October–November) coincide with serious emissions of small anthropogenic aerosols. While in DJF (December–January–February), the composition of the atmosphere was a mixture of dust particles and polluted aerosols released by domestic heating; the average AOD and αwere 0.29 ± 0.02 and 0.66 ± 0.17, respectively. Different air masses exhibited different degrees of influence on the aerosol concentration over Dunhuang in different seasons. During MAM, ranges of AOD (0.11–1.18) and α(0.06–0.82) were the largest under the dust influence of northwest-short-distance air mass in the four trajectories. Urban aerosols transported by northwest-short-distance air mass accounted for a very large proportion in JJA and the mixed aerosols observed in SON were mainly conveyed by air masses from the west. In DJF, the similar ranges of AOD and αunder the three air mass demonstrated the analogous diffusion effects on regional pollutants over Dunhuang. 2012年中国气溶胶综合特性观测网 (CARE-China)敦煌站气溶胶光学特性观测分析结果表明:该地区500nm波段AOD年均值为0.32 ± 0.06, 波长指数(α)年均值为0.73 ± 0.27. 敦煌地区气溶胶光学特性呈现显著季节变化特征. 春季多沙尘天气, AOD达到最大季节均值0.41 ± 0.04, 相应α值较小, 为0.44 ± 0.04; 夏秋两季是旅游旺季, 大量游客涌入及机动车的使用排放大量人为气溶胶粒子; 冬季出现沙尘粒子和家用燃煤取暖排放的细粒子的复合型污染, AOD和α分别为0.29 ± 0.02和0.66 ± 0.17. 不同季节不同气团对该地区气溶胶浓度影响不同. 春季, 西北短程气团裹挟大量沙尘粒子影响敦煌地区, AOD和α变化范围最大, 分别为0.11–1.18和0.06–0.82; 夏季西北短程气团携带大量城市气溶胶污染敦煌地区, 而秋季主要来自西方气团对混合气溶胶的输送影响; 冬季三种气团作用下, AOD和α变化范围相似, 表明冬季不同来向气团对局地污染物具有相同的扩散作用.

Ultraviolet (UV) radiation has significant effects on ecosystems, environments, and human health, as well as atmospheric processes and climate change. Two ultraviolet radiation datasets are described in this paper. One contains hourly observations of UV radiation measured at 40 Chinese Ecosystem Research Network stations from 2005 to 2015. CUV3 broadband radiometers were used to observe the UV radiation, with an accuracy of 5%, which meets the World Meteorology Organization’s measurement standards. The extremum method was used to control the quality of the measured datasets. The other dataset contains daily cumulative UV radiation estimates that were calculated using an all-sky estimation model combined with a hybrid model. The reconstructed daily UV radiation data span from 1961 to 2014. The mean absolute bias error and root-mean-square error are smaller than 30% at most stations, and most of the mean bias error values are negative, which indicates underestimation of the UV radiation intensity. These datasets can improve our basic knowledge of the spatial and temporal variations in UV radiation. Additionally, these datasets can be used in studies of potential ozone formation and atmospheric oxidation, as well as simulations of ecological processes.

We implemented the online coupled WRF-Chem model to reproduce the 2013 January haze event in North China, and evaluated simulated meteorological and chemical fields using multiple observations. The comparisons suggest that temperature and relative humidity (RH) were simulated well (mean biases are–0.2K and 2.7%, respectively), but wind speeds were overestimated (mean bias is 0.5 m∙s–1). At the Beijing station, sulfur dioxide (SO2) concentrations were overpredicted and sulfate concentrations were largely underpredicted, which may result from uncertainties in SO2emissions and missing heterogeneous oxidation in current model. We conducted three parallel experiments to examine the impacts of doubling SO2emissions and incorporating heterogeneous oxidation of dissolved SO2by nitrogen dioxide (NO2) on sulfate formation during winter haze. The results suggest that doubling SO2emissions do not significantly affect sulfate concentrations, but adding heterogeneous oxidation of dissolved SO2by NO2substantially improve simulations of sulfate and other inorganic aerosols. Although the enhanced SO2to sulfate conversion in the HetS (heterogeneous oxidation by NO2) case reduces SO2concentrations, it is still largely overestimated by the model, indicating the overestimations of SO2concentrations in the North China Plain (NCP) are mostly due to errors in SO2emission inventory.

The alpine wetlands on the Tibetan Plateau (TP) constitute 30% of China's wetlands, and previous studies have considered these wetlands to be important sources of CH4, based on several swamp measurements from the eastern edges of the plateau. However, the alpine wetlands consist of both swamps (9.5%) and swamp meadows (79.8%). In this study, the CH4fluxes of a swamp meadow and a swamp were determined. The results showed that the swamp meadow emitted much less CH4(130.8 ± 123.9 µg m−2h−1) than the swamp (2795.2 ± 796.4 µg m−2h−1). The CH4fluxes within the swamp meadow showed distinct microscale spatial heterogeneity: the hollow terrain released CH4, while the hummocks absorbed CH4; this pattern was explained well by soil moisture. The CH4emissions in the swamp meadow were highly sensitive to soil temperature variation (Q10= 3.62), while they were more sensitive to soil moisture in the swamp. By summarizing existing measurements, and considering the differences in CH4emissions from swamp meadows and swamps, the emissions of CH4from alpine wetlands across the TP were recalculated to range from 0.215 to 0.412 Tg CH4a−1, lower than previous studies. By comparison, the CH4uptake by nonwetland ecosystems ranges from −0.68 to −0.53 Tg CH4a−1. Therefore, this study conveys a notion that the alpine wetlands on the TP may not be significant CH4sources. However, further studies are needed to reduce the uncertainty regarding CH4emissions. The swamp meadows constitute 79.8% of the alpine wetlands in TibetWe found much lower CH4emissions from swamp meadow than swampOur reevaluation suggests that the Tibet is not a major CH4source

When gasoline is burned to power an automotive engine, a portion of the fuel remains unburned or is partially burned and leaves the engine as hydrocarbon and oxygenated compounds. In addition, a small portion of the fuel can escape the vehicle through evaporation. Changes in alkanes, olefins and aromatics each affect emissions differently, which could complicate control strategies for air pollution. In this study, we collected 31 gasoline samples over five provinces and cities (Beijing, Tianjin, Hebei, Shandong, and Shaanxi) in North China between 2012 and 2013. The organic composition of the gasoline samples was analyzed using the gas chromatography-mass spectrometry (GC-MS) method, and the aniline compounds were analyzed by solvent extraction and the GC-MS method. The ratios of alkanes, aromatics, olefins and other organic compounds in gasoline were 40.6%, 38.1%, 12.9% and 8.4%, respectively. The aromatic and benzene exceedances were 15 and 8 based on the China’s gasoline standards (III), and they accounted for 48.4% and 25.8% of all the gasoline samples, respectively. Strong carcinogen aniline compounds were detected in all 31 samples, and the content of aniline compounds in 3 samples exceeded 1%. The high proportion of aromatics and olefins in the gasoline increased the emissions of carbon monoxide (CO) and toxics, as well as the atmospheric photochemical reactivity of exhaust emissions, which could hasten the formation of secondary pollutants. Our results are helpful for redefining government strategies to control air pollution in North China and relevant for developing new refining technology throughout China.

Fine particle of organic aerosol (OA), mostly arising from pollution, are abundant in Beijing. To achieve a better understanding of the difference in OA in summer and autumn, a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS, Aerodyne Research Inc., USA) was deployed in urban Beijing in August and October 2012. The mean OA mass concentration in autumn was 30±30 μg m−3, which was higher than in summer (13±6.9 μg m−3). The elemental analysis found that OA was more aged in summer (oxygen-to-carbon (O/C) ratios were 0.41 and 0.32 for summer and autumn, respectively). Positive matrix factorization (PMF) analysis identified three and five components in summer and autumn, respectively. In summer, an oxygenated OA (OOA), a cooking-emission-related OA (COA), and a hydrocarbon-like OA (HOA) were indentified. Meanwhile, the OOA was separated into LV-OOA (low-volatility OOA) and SV-OOA (semi-volatile OOA); and in autumn, a nitrogen-containing OA (NOA) was also found. The SOA (secondary OA) was always the most important OA component, accounting for 55% of the OA in the two seasons. Back trajectory clustering analysis found that the origin of the air masses was more complex in summer. Southerly air masses in both seasons were associated with the highest OA loading, while northerly air masses were associated with the lowest OA loading. A preliminary study of OA components, especially the POA (primary OA), in different periods found that the HOA and COA all decreased during the National Day holiday period, and HOA decreased at weekends compared with weekdays.

We used the global atmospheric chemical transport model, GEOS-Chem, to simulate the spatial distribution and seasonal variation of surface-layer methane (CH4) in 2004, and quantify the impacts of individual domestic sources and foreign transport on CH4concentrations over China. Simulated surface-layer CH4concentrations over China exhibit maximum concentrations in summer and minimum concentrations in spring. The annual mean CH4concentrations range from 1800 ppb over western China to 2300 ppb over the more populated eastern China. Foreign emissions were found to have large impacts on CH4concentrations over China, contributing to about 85% of the CH4concentrations over western China and about 80% of those over eastern China. The tagged simulation results showed that coal mining, livestock, and waste are the dominant domestic contributors to CH4concentrations over China, accounting for 36%, 18%, and 16%, respectively, of the annual and national mean increase in CH4concentration from all domestic emissions. Emissions from rice cultivation were found to make the largest contributions to CH4concentrations over China in the summer, which is the key factor that leads to the maximum seasonal mean CH4 concentrations in summer.

In January 2013, a long-lasting episode of severe haze occurred in central and eastern China, and it attracted attention from all sectors of society. The process and evolution of haze pollution episodes were observed by the “Forming Mechanism and Control Strategies of Haze in China” group using an intensive aerosol and trace gases campaign that simultaneously obtained data at 11 ground-based observing sites in the CARE-China network. The characteristics and formation mechanism of haze pollution episodes were discussed. Five haze pollution episodes were identified in the Beijing-Tianjin-Hebei (Jing-Jin-Ji) area; the two most severe episodes occurred during 9–15 January and 25–31 January. During these two haze pollution episodes, the maximum hourly PM2.5mass concentrations in Beijing were 680 and 530 μg m−3, respectively. The process and evolution of haze pollution episodes in other major cities in the Jing-Jin-Ji area, such as Shijiazhuang and Tianjin were almost the same as those observed in Beijing. The external cause of the severe haze episodes was the unusual atmospheric circulation, the depression of strong cold air activities and the very unfavorable dispersion due to geographical and meteorological conditions. However, the internal cause was the quick secondary transformation of primary gaseous pollutants to secondary aerosols, which contributed to the “explosive growth” and “sustained growth” of PM2.5. Particularly, the abnormally high amount of nitric oxide (NOx) in the haze episodes, produced by fossil fuel combustion and vehicle emissions, played a direct or indirect role in the quick secondary transformation of coal-burning sulphur dioxide (SO2) to sulphate aerosols. Furthermore, gaseous pollutants were transformed into secondary aerosols through heterogeneous reactions on the surface of fine particles, which can change the particle’s size and chemical composition. Consequently, the proportion of secondary inorganic ions, such as sulphate and nitrate, gradually increased, which enhances particle hygroscopicity and thereby accelerating formation of the haze pollution.

In situmeasured data of broadband solar radiation (Rs) and ultraviolet (Uv) radiation were used to investigate the spatiotemporal variation properties of Uvradiation and the ratio of Uvradiation to Rsover the North China Plain (NCP). Based on the analysis, an empirical model for estimating Uvradiation under all weather conditions in this region was developed. The results showed that the annual Uvradiation over the NCP ranges from 0.38–0.52 MJ m−2d−1. The highest value during the study period was recorded at the Changwu site, which is located near the margin of the Loess Plateau, while the lowest value appeared at the station in Beijing. The seasonal variation pattern of the ratio of Uvradiation to Rsis similar to that of Uvradiation; namely, the highest value appears in August and then decreases gradually until the lowest value appears in November. A small increasing trend in the Uvradiation levels and the ratio of Uvradiation to Rswas observed over the NCP. The evaluation results showed that the empirical estimation model can be widely used to estimate Uvradiation under all atmospheric conditions. The relative error between the modeled and measured daily values were within ±15%.

Smog chamber experimental systems, which have been widely used in laboratory simulation for studying atmospheric processes, are comprehensively reviewed in this paper. The components, development history, main research topics and main achievements of smog chambers are introduced. Typical smog chambers in the world, including their volumes, wall materials, light sources and features, are summarized and compared. Key factors of smog chambers and their influences on the simulation of the atmospheric environment are discussed, including wall loss, wall emission and background pollutants. The features of next-generation smog chambers and their application prospect in future studies of the atmospheric environment are also outlined in this paper.This review summarizes the key features of smog chambers and their application in atmospheric process studies, bringing new insights into development directions for next-generation smog chambers.

There is an increasing concern over the impact of human-related emissions on the acid precipitation in China. However, few measurements have been conducted so far to clarify the acid-neutralization of precipitation on a regional scale. Under a network of 10 sites across Northern China operated during a 3-year period from December 2007 to November 2010, a total of 1118 rain and snow samples were collected. Of this total, 28% was acid precipitation with pH <5.6. Out of these acid samples, 53% were found heavily acidic with pH value below 5.0, indicating significantly high levels of acidification of precipitation. Most of the acidity of precipitation was caused by H2SO4and HNO3, their relative contribution being 72% and 28%, respectively. However, the contribution of HNO3to precipitation acidity will be enhanced due to the increasing NOxand stable SO2emissions in future. Neutralization factors for K+, NH4+, Ca2+, Na+, and Mg2+were estimated as 0.06, 0.71, 0.72, 0.15, and 0.13, respectively. The application of multiple regression analysis further quantified higher NH4+and Ca2+contribution to the neutralization process, but the dominant neutralizing agent varied from site to site. The neutralization was less pronounced in the rural than urban areas, probably due to different levels of alkaline species, which strongly buffered the acidity. Presence of high concentrations of basic ions was mainly responsible for high pH of precipitation with annual volume-weighted mean (VWM) values larger than 5.6 at several sites. It was estimated that in the absence of buffering ions, for the given concentration of SO42−and NO3−, the annual VWM pH of precipitation would have been recorded around 3.5 across Northern China. This feature suggested that emissions of particles and gaseous NH3played very important role in controlling the spatial variations of pH of precipitation in the target areas.ImplicationsAcid precipitation has long been recognized as a serious environmental problem in East Asia, especially in China. The present study identifies that acidity of precipitation in Northern China generated by H2SO4and HNO3was primarily neutralized by Ca2+and NH4+. However, in the future, acidity due to HNO3may increase as a result of the increasing trends of NOxand stable trends of SO2emissions in megacities. The reducing primary emissions of particles and gaseous ammonia may offer more clear-sky days in urban areas, but might also lead to enhanced acid precipitation in Northern China in the near future.

Secondary inorganic aerosol (especially SNA: sulfate, nitrate, and ammonium) formed from different pathways, account for significant proportions of ambient particulate matter during haze events. For the first time, we quantitatively explored contributions from different SNA formation pathways by an online monitoring AMS instrument and 3‐dimension factor analysis PMF3 model, which is called “SNA formation pathway apportionment”. Three formation process were identified: NH4NO3heterogeneous phase reactions (NH4NO3‐heter), (NH4)2SO4gas phase reactions ((NH4)2SO4‐gas), and mixed NH4NO3and (NH4)2SO4aqueous phase processes (S&N‐aque). Their overall contributions to SNA were 25.7%, 22.1%, and 52.2%, respectively. Moreover, (NH4)2SO4‐gas contributed mainly in clean (52.1%); S&N‐aque got the highest contribution in haze episode (69.6%); while sulfate gas phase formations were also found in haze stage (10.3%). The quantitative findings from this work provide hard evidence that aqueous phase processes (including sulfate aqueous phase reactions and nitrate gas‐particle partition) were major drivers for SNA increasing. Secondary inorganic aerosol (particularly SNA: sulfate, nitrate and ammonium) was found to be the main component of particulate matter in northern China. SNA can be formed through different reaction pathways, such as gas phase, aqueous phase, and heterogeneous reactions pathways. However, quantitative assessments of different pathways are still lacking, especially during different pollution processes. In this work, AMS data with high time resolution and three‐dimension receptor model (PMF3) were used to study the characteristics of secondary aerosols in winter in Beijing and make SNA formation pathway contribution apportionment. Three possible formation pathways were identified by PMF3: Heterogeneous reactions pathway of NH4NO3, gas phase reactions pathway of (NH4)2SO4, and aqueous phase processes of mixed NH4NO3& (NH4)2SO4, respectively. We found that the main dominant factors were diverse during different periods: (NH4)2SO4gas phase reactions pathway contributed mainly to SNA in clean period; mixed NH4NO3and (NH4)2SO4aqueous phase processes contributed mostly in haze episode. The methods and findings of this work enable and further our understandings on the formations of secondary inorganic aerosol in haze. Mixed NH4NO3and (NH4)2SO4(aqueous phase process) had the highest contribution during winter haze period (69.6%)(NH4)2SO4(gas phase formation pathway) contributed mainly in clean (52.1%)(NH4)2SO4(gas phase formation pathway) was also found during haze pollution stage (10.3%) Mixed NH4NO3and (NH4)2SO4(aqueous phase process) had the highest contribution during winter haze period (69.6%) (NH4)2SO4(gas phase formation pathway) contributed mainly in clean (52.1%) (NH4)2SO4(gas phase formation pathway) was also found during haze pollution stage (10.3%)

Measurements of greenhouse gases CO2, CH4, and N2O were made by static chamber-gas Chromatograph in Inner Mongolia. Results indicate that with growing seasons, the daily variation patterns of emission/uptake of greenhouse gases differ greatly in the prairie ecosystem. The peak of seasonal emission/uptake of three greenhouse gases occurs at the molting period in spring when soil moisture is high and rainfall is rich. The daily emissions of CO2from steppe vegetation in growing seasons are low during the daytime and high at night. Higher temperatures are advantageous to emission of CO2, as aboveground biomass determines the amount of CO2photosynthetic uptake. The key factors that influence the daily variation patterns of CH4uptake and N2O emission in serniarid grassland are soil moisture and the oxygen supplying condition, while the changes in daily temperature mainly affect the range of daily variations. The seasonal changes of N2O emission are positively related to seasonal change in soil moisture. Free grazing reduces the daily mean deviation of exchange rates of CO2, N2O, and CH4, but it decreases the amount of annual emission/uptake of N2O and CH4yet it increases the annual emission of CO2.

Abstract. To identify the key soil parameters influencing N₂O emission from the wheat-growing season, an outdoor pot experiment with a total of 18 fertilized Chinese soils planted with wheat was conducted in Nanjing, China during the 2000/2001 wheat-growing season. Average seasonal N₂O-N emission for all 18 soils was 610 mg m^-2, ranging from 193 to 1,204 mg m^-2, approximately a 6.2-fold difference between the maximum and the minimum. Correlation analysis indicated that the seasonal N₂O emission was negatively correlated with soil organic C (r²=0.5567, P&lt;0.001), soil total N (r²=0.4684, P&lt;0.01) and the C:N ratio (r²=0.4530, P&lt;0.01), respectively. A positive dependence of N₂O emission on the soil pH (r²=0.3525, P&lt;0.01) was also observed. No clear relationships existed between N₂O emission and soil texture, soil trace elements of Fe, Cu and Mg, and above-ground biomass of the wheat crop at harvest. A further investigation suggested that the seasonal N₂O-N emission (E, mg m^-2) can be quantitatively explained by E=1005-34.2SOC+4.1S_a (R²=0.7703, n=18, P=0.0000). SOC and S_a represent the soil organic C (g kg^-1) and available S (mg kg^-1), respectively.