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As air quality has improved rapidly in recent years, the public has become more interested in whether a famous snow peak, Yaomei Feng on the Tibetan Plateau, can be seen from Chengdu, a megacity located on the western plain of the Sichuan Basin, east of the plateau. Therefore, a threshold-method-based forecasting system for snow peak sighting was developed in this study. Variables from numerical models, including cloud–water mixing ratio, cloud cover over snow peak, water mixing ratio, PM2.5 concentration, and ground solar radiation, were used in the snow peak sighting forecast system. Terrain occlusion rate of each model grid was calculated. Monte Carlo simulations were applied for threshold determination. A WRF-CMAQ hindcast was conducted for 2020, owing to insufficient observation data, hindcast results on the snow peak sighting were compared with posts collected from social media. Estimations showed that the snow peak sighting forecast system performed well in reflecting the monthly trend of snow peak sightings, and the hindcast results matched the daily observations, especially from May to August. Accuracy of the snow peak sighting forecast model was 78.9%, recall value was 57.1%, and precision was 24.4%. [ABSTRACT FROM AUTHOR]

The Three Gorges Dam's construction and industrial transfer have resulted in a new air pollution pattern with the potential to threaten the reservoir eco-environment. To assess the impact of socioeconomic factors on the pattern of air quality vairation and economical risks, concentrations of SO, NO, and PM, industry genres, and meteorological conditions were selected in the Three Gorges Reservoir of Chongqing (TGRC) during 2006-2015. Results showed that air quality had improved to some extent, but atmospheric NO showed an increased trend during 2011-2015. Spatially, higher atmospheric NO extended to the surrounding area. The primary industry, especially for agriculture, had shown to be responsible for the remarkable increase of atmospheric NO ( p < 0.01) due to the direct burning of agricultural straws and the emission of livestock breeding. The improvement of regional industrial structure and industrialization benefited air pollutant reductions, but construction industries had inhibited the improvement of regional air quality. In the tertiary industry, the cargo industry at ports had significantly decreased atmospheric NO as a result of eliminating the obsoleted small ships. Contrarily, the highway transportation had brought more air pollutants. The relative humidity was shown to be the main meteorological factor, which had an extremely remarkable relation with atmospheric SO ( p < 0.01) and a significant correlation with atmospheric NO ( p < 0.05), respectively. In the future, the development of agriculture and livestock breeding would make regional air quality improvement difficult, and atmospheric SO, NO, and PM deposition would aggravate regional soil and water acidification and reactivate heavy metal in soil and sediment, further to pose a high level of ecological risk in the TGRC and other countries with reservoirs in the world. [ABSTRACT FROM AUTHOR]

A first study of nonmethane hydrocarbons (NMHCs) on hazy and normal days was performed in Foshan for providing deep insight into the local deteriorating air quality. Ethane, propane, i-pentane, ethene, propene, ethyne, benzene, and toluene were eight most abundant compounds, accounting for 71%-85% of total NMHCs. Most hydrocarbons showed much higher levels on hazy days than normal days together with hydrocarbon/ethyne ratios and diurnal variations, indicating hazy days are more dominated by vehicular emission. Correlation coefficients ( R2) of ethane, propane, ethane, propene, benzene, and total NMHCs with ethyne were 0.62-0.83, indicating these compounds are mainly related to vehicular emission. R2 analysis indicated that solvent usage is responsible for toluene and other aromatic hydrocarbons (e.g., ethylbezene). Benzene/toluene (B/T) ratio was 0.44±0.23 during whole sampling periods, again indicating vehicular emission is the dominant source. Lower B/T ratio (0.30±0.14) on hazy days than that (0.58±0.21) on normal days suggested that solvent usage emitted toluene. [ABSTRACT FROM AUTHOR]

Ground-level ozone (O3), which is mainly from the photochemical reactions of NOx and volatile organic compounds (VOCs), has become a crucial pollutant obstructing air quality improvement in China. Understanding the composition, temporal variability and source apportionment of VOCs is necessary for determining effective control measures to minimize VOCs and their related photochemical pollution. To provide a comprehensive analysis of VOC sources and their contributions to ozone formation in the city of Chengdu—a megacity with the highest rates of industrial and economic development in southwest China—we conducted a one-month monitoring project at three urban sites (Shuangliu, Xindu, Junpingjie; SL, XD and JPJ, respectively) along the main north–south meteorological transport channel before and during the implemented control measures. Alkanes were the dominant group at each site, contributing to around 50% of the observed total VOCs, followed by oxygen-containing VOCs (OVOCs), aromatics, halohydrocarbons and alkenes. During the control period, the mixing ratios of most measured VOC species decreased, and O3 concentrations were down by at least 20%. VOC species experiencing the most effect from control were aromatics and OVOCs, which had higher O3 formation reactivity. This indicated that the control policies had significant influence on reductions of reactive VOC species. We also identified VOC sources at SL and XD using positive matrix factorization (PMF) and assessed their contributions to photochemical O3 formation by calculating the O3 formation potential (OFP) based on mass concentrations and maximum incremental reactivity of related VOCs. Five dominant VOC sources were identified, with the highest contributions from vehicular exhaust and fuel evaporation before control, followed by solvent utilization, biogenic background and secondary formation, and industrial emissions. Contribution from vehicular exhaust was reduced the most at SL, while at XD, secondary formation VOCs decreased significantly. VOCs from vehicular and industrial emissions and solvent utilization were found to be the dominant precursors for OFPs, particularly the species of xylenes, toluene and propene. Our results therefore suggest that priority should be given to the alleviation of photochemical pollutants for effective control of O3 formation in Chengdu. The findings from this work have important implications for formulating effective emission control policies in Chengdu. [ABSTRACT FROM AUTHOR]

In September 2018, China's air quality monitoring protocol was amended from the standard conditions to actual conditions for particulate matter and to reference conditions for gaseous pollutants. Due to the amendment, the reported concentrations of the gaseous pollutants decreased by a constant rate of 8.4%, and the averages of PM2.5 (particulate matter that has an aerodynamic diameter of 2.5 microns or smaller) reported during September 2017 and August 2018 decreased by 7.9 ± 6.1% at 99% of the monitoring stations. Comparing the periods before and after the amendment, the 12-month PM2.5 concentrations at 17.2% of the stations actually increased despite appearing to decrease if the amendments were not considered. We reviewed 370 papers published in 2020 that utilized this air quality dataset, and 21% of these papers used the data before and after the amendment without explicitly stating whether or how conversions were conducted. It is urgent to widely broadcast the protocol amendment to ensure proper use of this extensively cited dataset. [ABSTRACT FROM AUTHOR]

Integral to the urban ecosystem, greening trees provide many ecological benefits, but the active biogenic volatile organic compounds (BVOCs) they release contribute to the production of ozone and secondary organic aerosols, which harm ambient air quality. It is, therefore, necessary to understand the BVOC emission characteristics of dominant greening tree species and their relative contribution to secondary pollutants in various urban contexts. Consequently, this study utilized a dynamic enclosure system to collect BVOC samples of seven dominant greening tree species in urban Chengdu, Southwest China. Gas chromatography/mass spectrometry was used to analyze the BVOC components and standardized BVOC emission rates of each tree species were then calculated to assess their relative potential to form secondary pollutants. We found obvious differences in the composition of BVOCs emitted by each species. Ficus virens displayed a high isoprene emission rate at 31.472 μgC/(gdw (g dry weight)•hr), while Cinnamomum camphora emitted high volumes of D-Limonene at 93.574 μgC/(gdw•hr). In terms of the BVOC emission rates by leaf area, C. camphora had the highest emission rate of total BVOCs at 13,782.59 μgC/(m2•hr), followed by Cedrus deodara with 5466.86 μgC/(m2•hr). Ginkgo biloba and Osmanthus fragrans mainly emitted oxygenated VOCs with lower overall emission rates. The high BVOC emitters like F. virens, C. camphora , and Magnolia grandiflora have high potential for significantly contributing to environmental secondary pollutants, so should be cautiously considered for future planting. This study provides important implications for improving urban greening efforts for subtropical Chinese urban contexts, like Chengdu. [Display omitted] [ABSTRACT FROM AUTHOR]

Surface ozone (O 3) has become a critical pollutant impeding air quality improvement in many Chinese megacities. Chengdu is a megacity located in Sichuan Basin in southwest China, where O 3 pollution occurs frequently in both spring and summer. In order to understand the elevated O 3 during spring in Chengdu, we conducted sampling campaign at three sites during O 3 pollution episodes in April. Volatile organic compounds (VOCs) compositions at each site were similar, and oxygenated VOCs (OVOCs) concentrations accounted for the highest proportion (35%-45%), followed by alkanes, alkens (including acetylene), halohydrocarbons, and aromatics. The sensitivity of O 3 to its precursors was analyzed using an observation based box model. The relative incremental reactivity of OVOCs was larger than other precursors, suggesting that they also played the dominant role in O 3 formation. Furthermore, the positive matrix factorization model was used to identify the dominant emission sources and to evaluate their contribution to VOCs in the city. The main sources of VOCs in spring were from combustion (27.75%), industrial manufacturing (24.17%), vehicle exhaust (20.35%), and solvent utilization (18.35%). Discussions on VOCs and NO x reduction schemes suggested that Chengdu was typical in the VOC-limited regime, and VOC emission reduction would help to prevent and control O 3. The analysis of emission reduction scenarios based on VOCs sources showed that the emission reduction ratio of VOCs to NO 2 needs to reach more than 3 in order to achieve O 3 prevention. Emission reduction from vehicular exhaust source and solvent utilization source may be more effective. [Display omitted] [ABSTRACT FROM AUTHOR]

Seventy-seven PM2.5 samples were collected at an urban site (Chongqing University Campus A) in October 2015 (autumn), December 2015 (winter), March 2016 (spring), and August 2016 (summer). These samples were analysed for organic carbon (OC), elemental carbon (EC), and their associated char, soot, 16 PAHs, and 28 n-alkanes to trace sources, and atmospheric transport pathways. The annual average of OC, EC, char, soot, ΣPAHs, and Σn-alkanes were 20.75 μg/m3, 6.18 μg/m3, 5.43 μg/m3, 0.75 μg/m3, 38.29 ng/m3, and 328.69 ng/m3, respectively. OC, ΣPAHs, and Σn-alkane concentrations were highest in winter and lowest in summer. EC, char, and soot concentrations were highest in autumn and lowest in winter. Source apportionment via positive matrix factorization (PMF) indicated that coal/biomass combustion-natural gas emissions (23.8%) and motor vehicle exhaust (20.2%) were the two major sources, followed by diesel and petroleum residue (21.1%), natural biogenic sources (17.7%), and evaporative/petrogenic sources (17.2%). The highest source contributor in autumn and winter was evaporative/petrogenic sources (30.6%) and natural biogenic sources (34.5%), respectively, whereas diesel engine emission contributed the most in spring and summer (32.1% and 38.0%, respectively). Potential source contribution function (PSCF) analysis identified southeastern Sichuan and northwestern Chongqing as the major potential sources of these pollutants. These datasets provide critical information for policymakers to establish abatement strategies for the reduction of carbonaceous pollutant emissions and improve air quality in Chongqing and other similar urban centres across China. • An obvious seasonal variation of carbonaceous aerosols was observed. • Qualitative sources apportioned using OC/EC and char/soot complemented well each other. • Five sources of OC, EC, PAHs and n-alkanes were apportioned using PMF. • PSCF identified southeast Sichuan and northwestern Chongqing as potential major source areas. [ABSTRACT FROM AUTHOR]

China is one of the regions with highest PM 2.5 concentration in the world. In this study, we review the spatio-temporal distribution of PM 2.5 mass concentration and components in China and the effect of control measures on PM 2.5 concentrations. Annual averaged PM 2.5 concentrations in Central-Eastern China reached over 100 μg m − 3 , in some regions even over 150 μg m − 3 . In 2013, only 4.1% of the cities attained the annual average standard of 35 μg m − 3 . Aitken mode particles tend to dominate the total particle number concentration. Depending on the location and time of the year, new particle formation (NPF) has been observed to take place between about 10 and 60% of the days. In most locations, NPF was less frequent at high PM mass loadings. The secondary inorganic particles (i.e., sulfate, nitrate and ammonium) ranked the highest fraction among the PM 2.5 species, followed by organic matters (OM), crustal species and element carbon (EC), which accounted for 6–50%, 15–51%, 5–41% and 2–12% of PM 2.5 , respectively. In response to serious particulate matter pollution, China has taken aggressive steps to improve air quality in the last decade. As a result, the national emissions of primary PM 2.5 , sulfur dioxide (SO 2 ), and nitrogen oxides (NO X ) have been decreasing since 2005, 2006, and 2011, respectively. The emission control policies implemented in the last decade could result in noticeable reduction in PM 2.5 concentrations, contributing to the decreasing PM 2.5 trends observed in Beijing, Shanghai, and Guangzhou. However, the control policies issued before 2010 are insufficient to improve PM 2.5 air quality notably in future. An optimal mix of energy-saving and end-of-pipe control measures should be implemented, more ambitious control policies for NMVOC and NH 3 should be enforced, and special control measures in winter should be applied. 40–70% emissions should be cut off to attain PM 2.5 standard. [ABSTRACT FROM AUTHOR]

PM 2.5 and its major chemical components, and light scattering (σ scat ) and absorption (σ abs ) coefficients were measured in Chengdu (CD) and Chongqing (CQ) in Sichuan Basin, from October 2014 to July 2015. Annual mean PM 2.5 , σ scat and σ abs were 67.0 ± 43.4 μg m − 3 , 421.4 ± 290.1 Mm − 1 and 36.7 ± 26.4 Mm − 1 , respectively, in CD, and annual mean PM 2.5 and σ abs were 70.9 ± 41.4 μg m − 3 and 45.4 ± 24.5 Mm − 1 , respectively, in CQ. PM 2.5 , σ scat and σ abs were all evidently higher in winter than in other seasons mainly due to the unfavorable meteorological conditions for dispersion of local pollutants. Diurnal patterns of σ scat and σ abs exhibited a peak value around 7:00–8:00 LT and a valley value around 17:00–18:00 LT. High levels of PM 2.5 accompanied with low wind speed and high relative humidity conditions were the major causes of visibility impairment in Sichuan Basin. Both σ scat and σ abs were remarkably higher under calm wind condition, indicating that local emissions were largely responsible for the aerosol pollutions in this region. High relative humidity enhanced extinction coefficient (b ext ) by up to around 1.6 and 1.4 times in CD and CQ, respectively, due to the hygroscopic growth of water soluble components. On annual basis, (NH 4 ) 2 SO 4 contributed the most to b ext , accounting for 34.4% and 31.5% in CD and CQ, respectively, followed by NH 4 NO 3 and organic matter, 28.1% and 17.5%, respectively, in CD, and 20.1% and 26.8%, respectively, in CQ. EC contributed about 10% and the rest contributed to < 12% at both urban sites. Therefore, reducing emissions of the precursor gases such as SO 2 , NO x , NH 3 and VOCs systemically may be efficient to improve the air quality and visibility simultaneously in Sichuan Basin. [ABSTRACT FROM AUTHOR]

Abstract: The concentrations of polycyclic aromatic hydrocarbons (PAHs) in PM2.5 and TSP were measured in Guangzhou during a typical haze episode. This episode included NH (non-haze, 3days), HFN (haze when air masses from north and northeast, 6days) and HFS (haze when air masses from south, 4days). The air quality in HFN was much worse than that in NH and HFS. The total average concentrations of PAHs in PM2.5 were 13.25ngm−3, 59.82ngm−3 and 13.09ngm−3 in NH, HFN and HFS, respectively. It indicated PAH pollution had been substantially aggravated by HFN. PAHs(5+6) were the most abundant compounds in HFN and HFS, which accounted for 55–75% of total concentration of PAHs, while PAHs(3+4) were the most abundant compounds in NH, which accounted for 54–67% of total concentration of PAHs. TEF (Toxic Equivalency Factors)-adjusted concentrations of 13 particulate PAHs were very high in HFN, indicating high health risks to humans for PAH exposure in HFN. The characteristic ratios of PAHs indicated coal combustion and traffic emission were the major contributors to PAHs in HFN and HFS. The concentrations of particulate PAHs in haze episode were strongly affected by wind speed and wind direction. PAHs in NH could be from long-range transport with high north wind speed, while local emission could be the main contributor of particle-associated PAHs in HFN. The transport speed of air masses was found to play an important role on PAH concentrations. [Copyright &y& Elsevier]

China has been performing nationwide social lockdown by releasing the Level 1 response to major public health emergencies (RMPHE) to struggle against the COVID-19 (SARS-CoV-2) outbreak since late January 2020. During the Level 1 RMPHE, social production and public transport were maintained at minimal levels, and residents stayed in and worked from home. The universal impact of anthropogenic activities on air pollution can be evaluated by comparing it with air quality under such extreme conditions. We investigated the concentration of both gaseous and particulate pollutants and aerosol light absorption at different levels of (RMPHE) in an urban area of southwestern China. During the lockdown, PM 2.5 , PM 10 , SO 2 , NO x , and BC decreased by 30–50%, compared to the pre-Level 1 RMPHE period. Meanwhile, the decrease of NO x caused the rise of O 3 by up to 2.3 times due to the volatile organic compounds (VOCs) limitation. The aerosol light absorption coefficient at multiple wavelengths decreased by 50%, and AAE decreased by 20% during the Level 1 RMPHE. BrC played essential roles in light absorption after the RMPHE was announced, accounting for 54.0% of the aerosol absorption coefficient at 370 nm. Moreover, the lockdown down-weighted the fraction of fossil fuel in BC concentrations to 0.43 (minima). This study characterizes air pollution at the most basic level and can provide policymakers with references for the "baseline." Unlabelled Image • During the COVID-19 lockdown, PM 2.5 , PM 10 , SO 2 , NO x , and BC decreased by 30–50%. • The decrease of NO x caused the rise of O 3 by up to 2.3 times due to the VOCs-limitation. • Basic power generation and industry provided ~47% of NO x and 68% of PM 2.5 during winter. • BrC accounted for 54.0% of the aerosol absorption coefficient at 370 nm during the lockdown. • The fraction of fossil fuel in BC concentrations dropped to 0.43. [ABSTRACT FROM AUTHOR]

While accumulating evidence shows that air pollution exposure is an important risk factor to influenza prevalence, their association has been inadequately investigated in mountainous regions with dense populations and high humidity. We aim to estimate the association and exposure-outcome effects between exposure to nitrogen dioxide (NO 2) and influenza prevalence in a mountainous region with a dense population and high humidity. We investigated 14,993 patients with confirmed influenza cases from January 2013 to December 2017 in Chongqing, a mountainous city in southwest China. We developed distributed lag non-linear models with quasi-Poisson link to take into account the lag and non-linear effects of NO 2 exposure on influenza prevalence. We estimated that the cumulative effect of a 10 μg/m3 increase in NO 2 with seven-day lag (i.e., summing all the contributions up to seven days) corresponded to relative risk of 1.24 (95% CI: 1.17–1.31) in daily influenza prevalence. Comparing to annual mean of the World Health Organization air quality guidelines of 40 μg/m3 for NO 2 , we estimated that 14.01% (95% CI: 10.69–17.08%) of the influenza cases were attributable to excessive NO 2 exposure. Our results suggest that NO 2 exposure could worsen the risk of influenza infection in this mountainous city, filling the gap of relevant researches in densely populated and mountainous cities. Our findings provide evidence for developing influenza surveillance and early warning systems. Image 1 • Influenza prevalence is associated with NO 2 exposure in a mountainous city. • Exposure-response effect is delineated with distributed lag nonlinear regression. • Distributed lag nonlinear effects over seven-day lag are modeled. • Cumulative effect of a 10 μg/m3 NO 2 increase corresponds to relative risk of 1.24 • Attributable fraction due to NO 2 exposure exceeding WHO AQG is 14.01%. [ABSTRACT FROM AUTHOR]