Evidence of aircraft activity impact on local air quality: A study in the context of uncommon airport operation

Wuhan Tianhe International Airport (WUH) was suspended to contain the spread of COVID-19,while Shanghai Hongqiao International Airport (SHA) saw a tremendousflight 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.NOx,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%and61.4%.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 NOxscatter 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 NOxemissions.

Elucidate long-term changes of ozone in Shanghai based on an integrated machine learning method

Surface ozone(O_(3))is influenced by regional background and local photochemical formation under favorable meteorological conditions.Understanding the contribution of these factors to changes in O_(3)is crucial to address the issue of O_(3)pollution.In this study,we propose a novel integrated method that combines random forest,principal component analysis,and Shapley additive explanations to distinguish observed O_(3)into meteorologically affected ozone(O_(3_MET)),chemically formed from local emissions(O_(3_LC)),and regional background ozone(O_(3_RBG)).Applied to three typical stations in Shanghai during the warm season from 2013 to 2021,the results indicate that O_(3_RBG)in Shanghai was 48.8±0.3 ppb,accounting for 79.6%–89.4%at different sites,with an overall declining trend of 0.018 ppb/yr.O_(3_LC)at urban and regional sites ranged from 5.9–9.0 ppb and 8.9–14.6 ppb,respectively,which were significantly higher than the contributions of 2.5–7.4 ppb at an upwind background site.O_(3_MET)can be categorized into those affecting O_(3)photochemical generation and those changing O_(3)dispersion conditions,with absolute contributions to O_(3)ranging from 13.4–19.0 ppb and 13.1–13.7 ppb,respectively.We found that the O_(3)rebound in 2017,compared to 2013,was primarily influenced by unfavorable O_(3)dispersion conditions and unbalanced emission reductions;while the O_(3)decline in 2021,compared to 2017,was primarily influenced by overall favorable meteorological conditions and further emissions reduction.These findings highlight the challenge of understanding O_(3)change due to meteorology and regional background,emphasizing the need for systematic interpretation of the different components of O_(3).

我国典型城市群O_3污染成因和关键VOCs活性解析

京津冀、长三角、珠三角和成渝地区四大城市群在夏秋季大气臭氧(O_3)污染问题严重.为了深入认识O_3的区域污染特征及其成因,在上述4个城市群于2014~2016年夏秋季节,开展了大气O_3及其前体物(氮氧化物(NOx)、挥发性有机物(VOCs))等的综合观测研究.观测发现,臭氧污染区域性明显,臭氧最大8h值在59~146(10^(-9)V/V),整体上城市站点臭氧浓度水平较郊区站点低,臭氧前体物NO2平均浓度水平在4~22(10^(-9)V/V),VOCs浓度为11~53(10^(-9)V/V),VOCs活性水平在1.6~10.5s^(-1).使用基于观测的盒子模型(OBM)分析臭氧生成控制区,发现四大城市群的O_3生成多数处于人为源VOCs控制区或者过渡区,且对烯烃和芳香烃的敏感性最强.运用PMF受体模型对城市站点VOCs来源进行解析,结果表明机动车尾气排放和汽油挥发是城市VOCs主要来源,占比30%~50%;溶剂涂料使用其次,占比为10%~20%.综合而言,我国现阶段臭氧污染防控应以VOCs控制为主,其中应着重控制机动车尾气排放和溶剂涂料使用.

Precursors and potential sources of ground-level ozone in suburban Shanghai

A high level of ozone(O3)is frequently observed in the suburbs of Shanghai,the reason for this high levei remains unclear.To obtain a detailed insight on the high level of 03 during summer in Shanghai,03 and its precursors were measured at a suburban site in Shanghai from July 1;2016 to July 31,2016.Using the Hybrid Single-Particle Lagrangian Integrated Trajectory,(HYSPLIT)model and concentration weighted trajectories(CW T),we found that Zhejiang province was the main potential source.of 03 in suburban Shanghai.When the sampling site was cotrolled by south-westerm winds exceeding 2 m/s,the O3-rich air masses from upwind regions(such as Zhejiang province)could be transported to the.suburban Shanghai.The propylene-equivalent concentation(PEC)and ozone formation potential(OFP)were,further calculated for each vOC species,and the resuts suggested that propylene,(m+p)-xylene,and.toluene played dominant roles in O3 formation.The Ozone Isopleth Plotting Research(OZIPR)model was used to reveal the impact ofO;precursors on O3 formation,and 4 base-cases were.selected to adjust the model simulaton.An average disparity.of 18.20%was achieved between the simulated and observed 03 concentrations.The 03 isopleth diagram ilustrated that 03 fomatin in July 2016 was in VOC-senstive regime,although the VOCNO,ratio was greater than 20.By intoducing sensitivity(S),a sensitvity analysis was performed for 03 formaton.We found.that 03 formation was senstive to propylene,(m+p)-xylene,e,o-xylene and toluene.The results provide theoretical suppot for 0;plluton treatment in Shanghai.

Response of PM_(2.5)-bound elemental species to emission variations and associated health risk assessment during the COVID-19 pandemic in a coastal megacity

The coronavirus(COVID-19)pandemic is disrupting the world from many aspects.In this study,the impact of emission variations on PM_(2.5)-bound elemental species and health risks associated to inhalation exposure has been analyzed based on real-time measurements at a remote coastal site in Shanghai during the pandemic.Most trace elemental species decreased significantly and displayed almost no diel peaks during the lockdown.After the lockdown,they rebounded rapidly,of which V and Ni even exceeded the levels before the lockdown,suggesting the recovery of both inland and shipping activities.Five sources were identified based on receptor modeling.Coal combustion accounted for more than 70%of the measured elemental concentrations before and during the lockdown.Shipping emissions,fugitive/mineral dust,and waste incineration all showed elevated contributions after the lockdown.The total non-carcinogenic risk(HQ)for the target elements exceeded the risk threshold for both children and adults with chloride as the predominant species contributing to HQ.Whereas,the total carcinogenic risk(TR)for adults was above the acceptable level and much higher than that for children.Waste incineration was the largest contributor to HQ,while manufacture processing and coal combustion were the main sources of TR.Lockdown control measures were beneficial for lowering the carcinogenic risk while unexpectedly increased the non-carcinogenic risk.From the perspective of health effects,priorities of control measures should be given to waste incineration,manufacture processing,and coal combustion.A balanced way should be reached between both lowering the levels of air pollutants and their health risks.

Insights into the formation of secondary organic carbon in the summertime in urban Shanghai

To investigate formation mechanisms of secondary organic carbon（SOC） in Eastern China,measurements were conducted in an urban site in Shanghai in the summer of 2015. A period of high O3 concentrations（daily peak 〉 120 ppb） was observed, during which daily maximum SOC concentrations exceeding 9.0 μg/（C·m^3）. Diurnal variations of SOC concentration and SOC/organic carbon（OC） ratio exhibited both daytime and nighttime peaks. The SOC concentrations correlated well with Ox（= O3＋ NO2） and relative humidity in the daytime and nighttime, respectively, suggesting that secondary organic aerosol formation in Shanghai is driven by both photochemical production and aqueous phase reactions. Single particle mass spectrometry was used to examine the formation pathways of SOC. Along with the daytime increase of SOC, the number fraction of elemental carbon（EC） particles coated with OC quickly increased from 38.1% to 61.9% in the size range of 250–2000 nm, which was likely due to gas-to-particle partitioning of photochemically generated semi-volatile organic compounds onto EC particles. In the nighttime, particles rich in OC components were highly hygroscopic, and number fraction of these particles correlated well with relative humidity and SOC/OC nocturnal peaks. Meanwhile, as an aqueous-phase SOC tracer, particles that contained oxalate-Fe（III） complex also peaked at night. These observations suggested that aqueous-phase processes had an important contribution to the SOC nighttime formation. The influence of aerosol acidity on SOC formation was studied by both bulk and single particle level measurements, suggesting that the aqueous-phase formation of SOC was enhanced by particle acidity.

Impact of meteorological conditions on a nine-day particulate matter pollution event observed in December 2013,Shanghai,China

A severe particulate matter pollution event occurred in Shanghai from 1 to 9 December 2013. The mean hourly mass concentrations of PM2.5 and PM10 were 211.9 and 249.0 μg/m3, respectively. Reanalysis data, in situ, and remote-sensing measurements were used to examine the impacts of meteorological conditions on this event. It was found that the synoptic pattern of weak pressure, the reduced planetary boundary layer height, and the passage of two cold fronts were key factors causing the event. Four stages were identified during this event based on the evolution of its PM2.5 levels and weather conditions. The highest concentration of PM2.5 （602 μg/m3） was observed in stage 3. High PM2.5 concentrations were closely associated with a low local ventilation index, with an average of 505 m2/s, as well as with the influx of pollutants from upstream, transported by the cold fronts.

Spatiotemporal variations of ambient air pollutants and meteorological influences over typical urban agglomerations in China during the COVID-19 lockdown

To investigate the air quality change during the COVID-19 pandemic,we analyzed spatiotemporal variations of six criteria pollutants in nine typical urban agglomerations in China using ground-based data and examined meteorological influences through correlation analysis and backward trajectory analysis under different responses.Concentrations of PM2.5,PM10,NO2,SO2 and CO in urban agglomerations respectively decreased by 18%–45%(30%–62%),17%–53%(22%–39%),47%-64%(14%–41%),9%–34%(0%–53%)and 16%-52%(23%–56%)during Lockdown(Post-lockdown)period relative to Pre-lockdown period.PM2.5 pollution events occurred during Lockdown in Beijing-Tianjin-Hebe(BTH)and Middle and South Liaoning(MSL),and daily O3 concentration rose to gradeⅡstandard in Post-lockdown period.Distinct from the nationwide slump of NO2 during Lockdown period,a rebound(~40%)in Post-lockdown period was observed in Cheng-Yu(CY),Yangtze River Middle-Reach(YRMR),Yangtze River Delta(YRD)and Pearl River Delta(PRD).With slightly higher wind speed compared with 2019,the reduction of PM2.5(51%–62%)in Post-lockdown period is more than2019(15%–46%)in HC(Harbin-Changchun),MSL,BTH,CP(Central Plain)and SP(ShandongPeninsula),suggesting lockdown measures are effective to PM2.5 alleviation.Although O3 concentrations generally increased during the lockdown,its increment rate declined compared with 2019 under similar sunlight duration and temperature.Additionally,unlike HC,MSL and BTH,which suffered from additional(>30%)air masses from surrounding areas after the lockdown,the polluted air masses reaching YRD and PRD mostly originated from the long-distance transport,highlighting the importance of joint regional governance.

Vertical distributions of wintertime atmospheric nitrogenous compounds and the corresponding OH radicals production in Leshan, southwest China

Ground-based multi-axis differential optical absorption spectroscopy(MAX-DOAS)observations were operated from 02 to 21 December 2018 in Leshan,southwest China,to measure HONO,NO_(2) and aerosol extinction vertical distributions,and these were the first MAX-DOAS measurement results in Sichuan Basin.During the measurement period,characteristic ranges for surface concentration were found to be 0.26-4.58 km^(−1) and averaged at 0.93 km^(−1) for aerosol extinction,0.49 to 35.2 ppb and averaged at 4.57 ppb for NO_(2) and 0.03 to 7.38 ppb and averaged at 1.05 ppb for HONO.Moreover,vertical profiles of aerosol,NO_(2) and HONO were retrieved from MAX-DOAS measurements using the Heidelberg Profile(HEIPRO)algorithm.By analysing the vertical gradients of pollutants and meteorological information,we found that aerosol and HONO are strongly localised,while NO_(2) is mainly transmitted from the north direction(city center direction).Nitrogen oxides such as HONO and NO_(2) are important for the production of hydroxyl radical(OH)and oxidative capacity in the troposphere.In this study,the averaged value of OH production rate from HONO is about 0.63 ppb/hr and maximum value of ratio between OH production from HONO and from(HONO+O_(3))is>93%before12:00 in Leshan.In addition,combustion emission contributes to 26%for the source of HONO in Leshan,and we found that more NO_(2) being converted to HONO under the conditions with high aerosol extinction coefficient and high relative humidity is also a dominant factor for the secondary produce of HONO.