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Abstract Fireworks displays are a traditional form of celebration during the Chinese Spring Festival (Festival). In response to the heavy air pollution caused by fireworks, Shanghai, a megacity in China, has imposed regulatory measures on the use of fireworks in recent years. To investigate air quality trends before and after firework regulation was established and quantify its efficiency, gaseous pollutants, PM 2.5 levels, and PM 2.5 chemical composition were synchronously measured at 1 h time intervals at an urban site and a suburban site in Shanghai in the period during and around the Festival from 2013 to 2017. PM 2.5 concentrations at the urban site during the Festival over the five-year period were 79 (max: 524), 94 (290), 53 (163), 50 (146) and 32 (156) μg/m3, respectively, presenting a decreasing trend at a rate of −13.8 μg/m3/yr (p = 0.05). K+ concentrations, which serve as a tracer of fireworks, were 8.2 (max: 159.4), 2.5 (14.6), 2.2 (10.4), 4.3 (44.2) and 0.8 (4.5) μg/m3 during the Festival from 2013 to 2017, respectively, and thus decreased at a rate of −1.3 μg/m3/yr (p = 0.17). Accordingly, fireworks contributed 41 (51.9%), 38 (36.5%), 6 (10.3%), 21 (35.6%), and 4 μg/m3 (12.1%) to PM 2.5 , respectively, implying the effectiveness of firework regulation in Shanghai. Health effects attributed to PM 2.5 pollution in Shanghai during the Festival were assessed based on Poisson regression. The number of premature deaths related to short-term PM 2.5 exposure in Shanghai during the Festival from 2013 to 2017 was 75 (95% CI: 27, 108), 92 (30, 129), 55 (18, 76), 49 (19, 70), and 31 (12, 45), respectively. Daily mortality due to PM 2.5 exposure during the Festival from 2013 to 2017 accounted for 1.4–3.8% of total daily mortality in Shanghai. This study provides scientific evidence of air quality improvement and the effectiveness of firework regulation in Shanghai. Graphical abstract Unlabelled Image Highlights • Significant air quality improvement was observed in Shanghai during the Festival from 2013 to 2017. • Fireworks contributed 41, 38, 6, 21 and 4 μg/m3 to PM 2.5 in Shanghai during the Festival from 2013 to 2017, respectively. • Health effects related to PM 2.5 exposure during the Festival was calculated based on Poisson regression. [ABSTRACT FROM AUTHOR]

• NO 2 concentrations were 77.3% lower during the closure of WUH. • Steeper reduction in NO than in BTEX levels at SHA. • NO 2 concentrations at WUH were dropped to near zero during airport closure. • Increase in O 3 levels at both WUH and SHA due to reduced NO x emissions. Wuhan Tianhe International Airport (WUH) was suspended to contain the spread of COVID-19, while Shanghai Hongqiao International Airport (SHA) saw a tremendous flight reduction. Closure of a major international airport is extremely rare and thus represents a unique opportunity to straightforwardly observe the impact of airport emissions on local air quality. In this study, a series of statistical tools were applied to analyze the variations in air pollutant levels in the vicinity of WUH and SHA. The results of bivariate polar plots show that airport SHA and WUH are a major source of nitrogen oxides. NO x , NO 2 and NO diminished by 55.8%, 44.1%, 76.9%, and 40.4%, 33.3% and 59.4% during the COVID-19 lockdown compared to those in the same period of 2018 and 2019, under a reduction in aircraft activities by 58.6% and 61.4%. The concentration of NO 2 , SO 2 and PM 2.5 decreased by 77.3%, 8.2%, 29.5%, right after the closure of airport WUH on 23 January 2020. The average concentrations of NO, NO 2 and NO x scatter plots at downwind of SHA after the lockdown were 78.0%, 47.9%, 57.4% and 62.3%, 34.8%, 41.8% lower than those during the same period in 2018 and 2019. However, a significant increase in O 3 levels by 50.0% and 25.9% at WUH and SHA was observed, respectively. These results evidently show decreased nitrogen oxides concentrations in the airport vicinity due to reduced aircraft activities, while amplified O 3 pollution due to a lower titration by NO under strong reduction in NO x emissions. Significantly reduced NO x concentrations and amplified O 3 pollution at the airfield boundary of Shanghai Hongqiao International Airport due to reduced aircraft activities. [Display omitted] [ABSTRACT FROM AUTHOR]

At the end of 2019, a novel coronavirus, designated as SARS-CoV-2, emerged in Wuhan, China and was identified as the causal pathogen of COVID-19. The epidemic scale of COVID-19 has increased dramatically, with confirmed cases increasing across China and globally. Understanding the potential affecting factors involved in COVID-19 transmission will be of great significance in containing the spread of the epidemic. Environmental and meteorological factors might impact the occurrence of COVID-19, as these have been linked to various diseases, including severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS), whose causative pathogens belong to the same virus family as SARS-CoV-2. We collected daily data of COVID-19 confirmed cases, air quality and meteorological variables of 33 locations in China for the outbreak period of 29 January 2020 to 15 February 2020. The association between air quality index (AQI) and confirmed cases was estimated through a Poisson regression model, and the effects of temperature and humidity on the AQI-confirmed cases association were analyzed. The results show that the effect of AQI on confirmed cases associated with an increase in each unit of AQI was statistically significant in several cities. The lag effect of AQI on the confirmed cases was statistically significant on lag day 1 (relative risk (RR) = 1.0009, 95% confidence interval (CI): 1.0004, 1.0013), day 2 (RR = 1.0007, 95% CI: 1.0003, 1.0012) and day 3 (RR = 1.0008, 95% CI: 1.0003, 1.0012). The AQI effect on the confirmed cases might be stronger in the temperature range of 10 °C ≤ T < 20 °C than in other temperature ranges, while the RR of COVID-19 transmission associated with AQI was higher in the relative humidity (RH) range of 10% ≤ RH < 20%. Results may suggest an enhanced impact of AQI on the COVID-19 spread under low RH. Unlabelled Image • AQI - COVID-19-confirmed cases association is statistically significant in some cities. • Lag effect of AQI on confirmed cases is statistically significant on lag 1–3 days. • AQI effect on the confirmed cases in temperature range of 10–20 °C may be stronger. • Impact of AQI on the spread of COVID-19 may be enhanced under low relative humidity. [ABSTRACT FROM AUTHOR]

CO 2 and CH 4 are the two most potent greenhouse gases (GHGs) in the atmosphere. They are frequently monitored at background observatories, but less so in urban areas, especially in China. In this study, the temporal variations of urban atmospheric CO 2 and CH 4 , including seasonal, weekly, and diurnal characteristics, were obtained based on one year of continuous measurement in the megacity Shanghai. Probable anthropogenic sources were further investigated through relationships among GHGs and atmospheric pollutants. Potential sources regions and transport pathways of GHGs were studied in association with meteorological conditions. The annual average concentrations of CO 2 and CH 4 were 428.36 ± 13.96 ppm and 2154 ± 190 ppb, respectively, which were higher than those at global and regional background observatories. The highest CO 2 concentration appeared in winter and the lowest in autumn, whereas CH 4 values were highest in summer and lowest in spring. Both CO 2 and CH 4 showed strong diurnal variations, but only CO 2 exhibited seasonal and weekly differences due to the variation of emission sources and plant photosynthesis in Shanghai and the surrounding Yangtze River Delta (YRD). CO 2 and combustion-derived air pollutants were co-emitted from similar sources and co-transported to the research site, as demonstrated by correlation analysis. Furthermore, the correlation analysis also suggested some neglected anthropogenic combustion sources of CH 4 in Shanghai, besides the traditional biogenic emissions from landfills, wetlands, paddy fields, and dairy farms. The anthropogenic CO 2 concentration in urban Shanghai estimated from a CO 2 -CO regression model was 14.98 ± 5.09 ppm, together with a background concentration of 413.31 ± 7.07 ppm, which was higher than at global background sites but lower than at the nearby regional background Lin'an station. GHGs were accumulated from local sources under stable weather conditions and transported from remote sources at high wind speeds. Air masses from "super-emitters" north and south of the observation site contributed most of the elevation in GHGs concentration above their annual averages. Considering the co-emissions of GHGs and air pollutants from carbon-containing material combustion and use, and the potential of methane to generate O 3 in the urban environment, reduction of CO 2 and CH 4 together with air pollutants could benefit both climate and air quality in Shanghai and the surrounding YRD. Unlabelled Image • CO 2 and CH 4 were measured together with air pollutants and meteorological conditions in urban Shanghai. • Both CO 2 and CH 4 showed diurnal variations, but only CO 2 showed seasonal and weekday effects. • Anthropogenic sources affected the elevated concentrations of GHGs in urban environment. • GHGs were accumulated from local sources in stable, together with transport from remote sources. • Joint control of GHGs and air pollutants could benefit both climate and air quality. [ABSTRACT FROM AUTHOR]

Assessing the impact of garbage classification on air pollution in rapidly developing economic regions is particularly necessary in light of the current policy trends. We evaluated the resulting changes in air pollution levels before and after garbage classification based on a three-year field observation using high-resolution online instruments in a municipal solid waste comprehensive disposal base. A targeted scheme is proposed to analyze the variation characteristics of major sources in a complex multi-source environment (Environments with multiple sources of pollution). We found that the concentrations of hydrogen sulfide (H 2 S) and volatile organic compounds (VOCs) in ambient air decreased by 48% and 43% respectively after garbage classification, and their spike frequency was controlled at approximately 0.01. The average H 2 S and VOC concentrations were generally low during the daytime, but relatively high during the nighttime because of meteorology and photochemistry. The ozone formation potential of the base decreased by 56%. Alternatively, emissions from transportation and combustion sources increased, while landfill pollution decreased owing to changes in the method of waste disposal. This finding suggests that garbage classification is an effective means of improving the air quality. This new scheme has a good potential in actual research scenarios. [Display omitted] [ABSTRACT FROM AUTHOR]

To combat urban challenges such as air pollution stemming from excessive vehicle use, policy makers have adopted various driving restriction policies (DRPs) worldwide. Although previous studies have extensively justified the effects of citywide DRPs on air quality, little attention has been paid to urban core-focused license-plate-based DRPs (UCLDRPs), which have gained increasing popularity among major cities. To bridge this gap, we carried out an empirical evaluation of the short-run effectiveness of Shanghai's UCLDRPs in improving air quality using difference-in-differences (DID) modeling approaches on high-frequency air quality data. The results show that UCLDRPs did not lead to any reduction of air pollutants including NO 2 , PM 2.5 , and PM 10 during peak hours (the restricted time window) in the inner ring area (the restricted area), while contributing to a 14% increase in the concentration of CO. Moreover, the air quality of surrounding zones (the 5 km buffer area) got worse as the concentration of CO and PM 10 raised by 16% and 8% respectively. Results also justified the temporal-spatial spillover effects in the dynamics: the concentrations of CO and PM 10 got increased by 10%-20% in the 5 km buffer area within time periods right before or after the restricted time windows. [ABSTRACT FROM AUTHOR]

The accuracy of atmospheric numerical model is important for the prediction of urban air pollution. This study investigated and quantified the uncertainties of meteorological and air quality model during multi-levels air pollution periods. We simulated the air quality of megacity Shanghai, China with WRF/CMAQ (Weather Research and Forecasting model and Community Multiscale Air Quality model) at both non-pollution and heavy-pollution episodes in 2012. The weather prediction model failed to reproduce the surface temperature and wind speed in condition of high aerosol loading. The accuracy of the air quality model showed a clear dropping tendency from good air quality conditions to heavily polluted episodes. The absolute model bias increased significantly from light air pollution to heavy air pollution for SO (from 2 to 14%) and for PM (from 1 to 33%) in both urban and suburban sites, for CO in urban sites (from 8 to 48%) and for NO in suburban sites (from 1 to 58%). A test of applying the Urban Canopy Model scheme to the WRF model showed fairly good improvement on predicting the meteorology field, but less significant effect on the air pollutants (6% for SO and 19% for NO decease in model bias found only in urban sites). This study gave clear evidence to the sensitivities of the model performance on the air pollution levels. It is suggested to consider this impact as a source for model bias in the model assessment and make improvement in the model development in the future. [ABSTRACT FROM AUTHOR]

China has > 400 ports, is home to 7 of 10 biggest ports in the world and its waterway infrastructure construction has been accelerating over the past years. But the increasing number of ports and ships means increasing emissions, and in turn, increasing impact on local and regional air pollution. This paper presents an overview of the broad field of ship emissions in China and their atmospheric impacts, including topics of ship engine emissions and control, ship emission factors and their measurements, developing of ship emission inventories, shipping and port emissions of the main shipping areas in China, and quantitative contribution of shipping emissions to the local and regional air pollution. There have been an increasing number of studies published on all the above aspects, yet, this review identified some critical research gaps, filling of which is necessary for better control of ship emissions, and for lowering their impacts. In particular, there are very few studies on inland ports and river ships, and there are few national scale ship emission inventories available for China. While advanced method to estimate ship emission based on ship AIS activities makes it now possible to develop high spatial- and temporal-resolution emission inventories, the ship emission factors used in Chinese studies have been based mainly on foreign measurements. Further, the contribution of ship emissions to air pollution in coastal cities, the dispersion of pollution plumes emitted by ships, or the chemical evolution process along the transmission path, have so far not been systematically studied in China. [ABSTRACT FROM AUTHOR]

Since the Action Plan for Air Pollution Prevention and Control (the Action Plan) was implemented at the end of 2013, the ambient air quality in China is significantly improved. However, PM 2.5 (particles with diameter ≤ 2.5 μm) levels in some cities still exhibit clear interannual oscillations. For example, the annual mean PM 2.5 levels in Shanghai decreased by 16.1% in 2014, while increased by 2.2% in 2015 according to year-on-year comparisons. To better understand the corresponding causes, the obliquely rotated T-mode principal component analysis (PCA) method and WRF-Chem model are jointly employed in this study. Results show that the west wind frequency and the accumulative wind (< 1.8 m/s) duration are the key indicators affecting local PM 2.5 transport and dispersion significantly. Moreover, four typical synoptic patterns conductive to PM 2.5 pollution are illustrated as mid-ward path cold (CM), eastward path cold (CE), L-share high (GL) and near high center (GC), in which GL is the most adverse circulation pattern. The year-on-year changes of meteorology have positive effects on PM 2.5 year-on-year variations. The significant decline of PM 2.5 levels in 2014 compared with those in 2013, as well as the obvious increase in 2015 compared with 2014, both well correspond to year-on-year variations of meteorological indicators. Model results present that PM 2.5 interannual variations result from the changes of meteorology during 2013 to 2015, are consistent with measured oscillations. By comparing measured and modeled PM 2.5 year-on-year variabilities, a greater PM 2.5 decreasing at 9.4% is estimated under favorable meteorological conditions, while a less increasing at 6% under unfavorable meteorological conditions due to emission reductions, indicating the initial improvement has been achieved by the Action Plan. Otherwise, since the current Action Plan has difficulties in completely offsetting the PM 2.5 rise attributed to the adverse weather, more stringent program should be drawn up for unfavorable meteorological conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Detecting O 3 -precursor sensitivity (OPS) is key for building O 3 control strategies. • We analyze the relationship between the HO 2 /OH indicator and OPS in the YRD. • WRF-CAMx and ensemble diagnostic tools reveal the mechanisms of this relationship. • HO 2 /OH can be used to identify OPS and quantify O 3 sensitivity to its precursors. Continued exacerbation of ozone (O 3) pollution in China has driven the urgent need for an emission control strategy that efficiently reduces O 3 levels. Determining O 3 precursor sensitivity (OPS) and its driving factors is a prerequisite for formulating effective O 3 control strategies. In this study, we proposed an atmospheric oxidative capacity-based indicator, HO 2 /OH, and demonstrated its effectiveness in indicating OPS over the Yangtze River Delta (YRD) of China by applying a localized comprehensive air quality model with extensions (CAMx) coupled with the Weather Research and Forecasting (WRF) model. A strong correlation was discovered between HO 2 /OH and OPS, and HO 2 /OH showed the best performance in separating NO x - and VOC-limited regimes in comparison with other commonly used indicators. A comprehensive analysis with ensemble diagnostic tools revealed the spatial heterogeneity of NO x and VOC emissions and the impact of regional transport controlling the relationship between OPS variations and the HO 2 /OH indicator over the YRD. The process analysis results show that days with higher contributions from horizontal advection favored OPS transitions in Shanghai, Nanjing, Hefei, Suzhou, and Wuhu, while vertical advection caused OPS transitions in Hangzhou and Ningbo. O 3 source apportionment technology analysis indicated that the regional contributions from Zhejiang and Jiangsu/Anhui corresponded well to the NO x -limited and VOC-limited regimes, respectively. Our results provide a better understanding of the underlying mechanisms of the relationship between OPS and the HO 2 /OH indicator and can help guide contingency control measures for O 3 despiking over the YRD and other photochemically active regions worldwide. [ABSTRACT FROM AUTHOR]

Abstract: A multi-year (2004–2008) study of horizontal visibility and factors controlling its variations was conducted in Shanghai. The seasonal average visibility in spring, summer, autumn, and winter was 7.7 km, 8.4 km, 8.1 km, and 6.5 km, respectively, significantly exceeding the haze criteria of 10 km throughout all four seasons. Although SO2 and NO2 concentrations gradually shifted to lower levels on an annual basis, no distinct improvement of the annual mean visibility was noticed. Via a grouping method, it was found that the water soluble ions and black carbon were the major contributors to haze formation while the role of mineral aerosol was negligible. Of the ions, SO4 2−, NO3 −, NH4 +, K+, and C2O4 2− were most associated with the formation of heavy haze. SO4 2− and NO3 − were both found to have significant decreasing trends with annual decreasing rates of 0.96 and 0.56 μg/m3/yr, respectively. Conversely, NH4 + showed a significant increasing trend with the annual increasing rate of 0.52 μg/m3/yr. Based on a quantitative correlation analysis, the roles of NH4 + and Ca2+ on the acids neutralization were almost equivalent in the earlier years of 2004–2005. While the role of Ca2+ had tremendously dropped to less than 23% in the later years of 2006–2008. Intense control measures on the emissions of construction works and roadside dust were the main driving force for the evident decreasing trend of annual Ca2+ concentrations. This study found that the gradual replacement of CaSO4 and Ca(NO3)2 by (NH4)2SO4 and NH4NO3 in aerosol was the major cause of no improvement of the visibility impairment in Shanghai during recent years. [Copyright &y& Elsevier]

Based on the concentrations of the carbonaceous components and the typical organic tracers in 682 p.m. 2.5 samples collected in Shanghai from 2012 to 2018, the temporal trends of the concentrations and potential sources of the secondary organic aerosols in PM 2.5 in Shanghai were investigated. The annual average concentrations of organic carbon (OC), elemental carbon (EC) and water-soluble organic carbon (WSOC) all showed a decreasing trend along with the PM 2.5 concentration. The annual concentration of total carbon (TC) in 2018 (4.3 μg m−3) was about 34% of that in 2012. Compared with that in 2013, the concentrations of isoprene and sesquiterpene SOA tracers in 2018 decreased by 48% and 43%. Meanwhile, the concentration of monoterpene SOA tracers kept stable in 2 ng m−3 to 3 ng m−3, and the concentration of toluene SOA tracer decreased slightly from 1.3 ng m−3 in 2013 to 1.0 ng m−3 in 2018. Correlation analysis with levoglucosan suggested that biomass burning should be an important source of sesquitertene in Shanghai. It was found that the 2-MGA/2-MTLs ratio of the isoprene tracers was more strongly affected by the ambient temperature but not NOx in Shanghai. The concentration of secondary organic carbon (SOC) estimated with OC/EC-based, WSOC-based and tracer-based methods showed a decreasing trend during the study period, but the contribution of SOC to OC was increasing. Anthropogenic aromatic volatile organic compounds was the increasingly important contributor to the SOC in PM 2.5 , and should be the key pollutants to be controlled to further improve the air quality in Shanghai. • Temporal trend of SOC in PM 2.5 in Shanghai during 2012 and 2018 investigated. • The concentration of SOC decreasing while the contribution to OC increasing in the last decade. • Relative contribution of SOA from toluene was found increased but not decreased. • Biomass burning was the important source of seisquiterpene in Shanghai. • 2-MG/2-MTLs ratio in urban environment strongly affected by ambient temperature. [ABSTRACT FROM AUTHOR]

To investigate the potential public health impact of ambient air pollution under various energy scenarios in Shanghai, we estimated the air pollution exposure level of the general population under various planned energy scenarios, and assessed the potential public health impact using the concentration–response functions derived from available epidemiologic studies. The results show that ambient air pollution in relation to various energy scenarios could have significant impact on the health status of Shanghai residents. Compared with base case scenario, implementation of various energy scenarios could prevent 608–5144 and 1189–10,462 PM10-related avoidable deaths (mid-value) in 2010 and 2020, respectively; and it could also decrease substantial cases of relevant diseases. These findings illustrate that an effective energy and environmental policy will play an active role in reduction of air pollutant emissions, improvement of air quality, and public health. [Copyright &y& Elsevier]

China's lockdown to control COVID-19 brought significant declines in air pollutant emissions, but haze was still a serious problem in North China Plain (NCP) during late-January to mid-February of 2020. We seek the potential causes for the poor air quality in NCP combining satellite data, ground measurements and model analyses. Efforts to constrain COVID-19 result in a drop-off of primary gaseous pollutants, e.g., −42.4% for surface nitrogen dioxide (NO 2) and −38.9% for tropospheric NO 2 column, but fine particulate matter (PM 25) still remains high and ozone (O 3) even increases sharply (+84.1%). Stagnant weather during COVID-19 outbreak, e.g., persistent low wind speed, frequent temperature inversion and wind convergence, is one of the major drivers for the poor air quality in NCP. The surface PM 2.5 levels vary between −12.9~+15.1% in NCP driven by the varying climate conditions between the years 2000 and 2020. Besides, the persistent PM 2.5 pollution might be maintained by the still intensive industrial and residential emissions (primary PM 2.5), and increased atmospheric oxidants (+26.1% for ozone and +29.4% for hydroxyl radical) in response to the NO 2 decline (secondary PM 2.5). Further understanding the nonlinear response between atmospheric secondary aerosols and NO x emissions is meaningful to cope with the emerging air pollution problems in China. Image 1 • Both satellite data and ground measurements confirm improved NO 2 air quality. • PM 2.5 varies between −12.9~+15.1% driven by climate conditions. • High PM 2.5 is maintained by intensive primary emission and increased oxidants. [ABSTRACT FROM AUTHOR]