Observation-based sources evolution of non-methane hydrocarbons (NMHCs) in a megacity of China

Both concentrations and emissions of many air pollutants have been decreasing due to implement of control measures in China,in contrast to the fact that an increase in emissions of non-methane hydrocarbons(NMHCs)has been reported.This study employed seven years continuous NMHCsmeasurements and the related activities data of Shanghai,a megacity in China,to explore evolution of emissions and effectiveness of air pollution control measures.The mixing ratio of NMHCs showed no statistical interannual changes,of which their compositions exhibited marked changes.This resulted in a decreasing trend of ozone formation potential by 3.8%/year(p<0.05,the same below),which should be beneficial to ozone pollution mitigation as its production in Shanghai is in the NMHCs-limited regime.Observed alkanes,aromatics and acetylene changed by+3.7%/year,-5.9%/year and-7.4%/year,respectively,and alkenes showed no apparent trend.NMHCs sources were apportioned by a positive matrix factorization model.Accordingly,vehicular emissions(-5.9%/year)and petrochemical industry emissions(-7.1%/year)decreased significantly,but the decrease slowed down;significant reduction in solvent usage(-9.0%/year)appeared after 2010;however,emissions of natural gas(+12.6%/year)and fuel evaporation(with an increasing fraction)became more important.The inconsistency between observations and inventories was found in interannual trend and speciation as well as source contributions,emphasizing the need for further validation in NMHCs emission inventory.Our study confirms the effectiveness of measures targeting mobile and centralized emissions from industrial sources and reveals a need focusing on fugitive emissions,which provided new insights into future air policies in polluted region.

Direct identification of total and missing OH reactivities from light-duty gasoline vehicle exhaust in China based on LP-LIF measurement

Considerable efforts have been devoted to characterising the chemical components of vehicle exhaust.However,these components may not accurately reflect the contribution of vehicle exhaust to atmospheric reactivity because of the presence of species not accounted for(“missing species”)given the limitations of analytical instruments.In this study,we improved the laser photolysis–laser-induced fluorescence(LP-LIF)technique and applied it to directly measure the total OH reactivity(TOR)in exhaust gas from light-duty gasoline vehicles in China.The TOR for China Ⅰ to Ⅵ-a vehicles was 15.6,16.3,8.4,2.6,1.5,and 1.6×10^(4) sec^(-1),respectively,reflecting a notable drop as emission standards were upgraded.The TOR was comparable between cold and warm starts.The missing OH reactivity(MOR)values for China Ⅰ to Ⅳ vehicles were close to zero with a cold start but were much higher with a warm start.The variations in oxygenated volatile organic compounds(OVOCs)under different emission standards and for the two start conditions were similar to those of the MOR,indicating that OVOCs and the missing species may have similar production processes.Online measurement revealed that the duration of the stable driving stage was the primary factor leading to the production of OVOCs and missing species.Our findings underscore the importance of direct measurement of TOR from vehicle exhaust and highlight the necessity of adding OVOCs and other organic reactive gases in future upgrades of emission standards,such that the vehicular contribution to atmospheric reactivity can be more effectively controlled.

Significant effects of transport on nanoparticles during new particle formation events in the atmosphere of Beijing

The mechanisms of new particle formation(NPF)events that occurred under high aerosol loadings(“polluted”NPF)in the atmosphere have been unclear,which has inhibited the precision of particlepollution control.To deepen the understanding of how the“polluted”NPF events occur,a one-monthcomprehensive measurement was conducted in the atmosphere of Beijing during the summer of2016.The“clean”NPF events(frequency=22%)(condensation sink,CS<0.015 s^(-1))were found to becaused by local nucleation and growth.The“polluted”NPF events(frequency=28%)(CS>0.015 s^(-1))were influenced by both local nucleation-growth and regional transport,and the contributions from thetwo factors to 6e25 nm particle number concentration were 60%and 40%,respectively.This studyemphasized the importance of the transport for nanoparticles in relatively polluted atmospheres,and forthat the regional joint particle pollution control would be an essential policy.

长江三角洲区域大气PM_(2.5)和臭氧污染协同控制路径

国家“碳达峰、碳中和”战略目标(以下简称“双碳”目标)的提出对长江三角洲(以下简称长三角)高质量一体化发展赋予了新的要求.本文基于长三角区域精细化排放清单和WRF-CMAQ模型,模拟了不同政策情景下区域空气质量改善情况.结果显示,绿色低碳情景(CP)较趋势照常情景(BAU)和末端强化情景(EP)具有更大的减排潜力,是实现绿色美丽长三角目标的重要路径.CP情景下,与2017年相比,预计2025年SO_(2)、NO_(x)、NMVOCs(non-methane volatile organic compounds)、一次PM_(2.5)排放将分别下降55.1%、26.5%、25.2%、27%;2035年,则将分别下降66%、56.4%、36.1%、39.4%.截至2035年,区域PM_(2.5)年均值和臭氧日8 h最大值第90百分位数(O_(3)-8 h 90th)将分别达到26和129μg m^(−3),50%地级市PM_(2.5)年均浓度将达到世界卫生组织第二阶段指导值.综合模拟结果,中长期全国和区域持续同步推动主要污染物的减排,将有望实现PM_(2.5)浓度持续改善和臭氧浓度的同步改善,实现协同减排的目标.近中期,绿色美丽长三角政策驱动的以末端治理为主的大气污染治理措施仍将继续对污染减排具有重要贡献,而中长期,由“双碳”目标驱动的能源、产业、交通结构调整措施对污染减排具有关键作用.持续大力推动NO_(x)和NMVOCs全面减排是实现PM_(2.5)与臭氧协同控制的关键.在延续现有严格的末端控制政策的基础上,进一步强化工业涂装、石化化工、橡塑、医药等涉挥发性有机物排放行业的产业结构调整,以及深入推进交通运输结构调整与加强新能源车船推广是中长期区域协同控制PM_(2.5)和臭氧的重要抓手.

Chemical characteristics of fine particles and their impact on visibility impairment in Shanghai based on a 1-year period observation

In this work, a one-year observation focusing on high time resolution characteristics of components in fine particles was conducted at an urban site in Shanghai. Contributions of different components on visibility impairment were also studied. Our research indicates that the major components of PM2.5 in Shanghai are water-soluble inorganic ions and carbonaceous aerosol, accounting for about 60% and 30% respectively. Higher concentrations of sulfate （SO42-） and organic carbon （OC） in PM2.s occurred in fall and summer, while higher concentrations of nitrate （NO3-） were observed in winter and spring. The mass concentrations of Cl- and K＋ were higher in winter. Moreover, NO3- increased significantly during PM2.s pollution episodes. The high values observed for the sulfate oxidizing rate （SOR）, nitrate oxidizing rate （NOR） and secondary organic carbon （SOC） in OC indicate that photochemical reactions were quite active in Shanghai. The IMPROVE （Interagency Monitoring of Protected Visual Environments） formula was used in this study to investigate the contributions of individual PM2.5 chemical components to the light extinction efficient in Shanghai. Both NH4NO3 and （NH4）aSO4 had close relationships with visibility impairment in Shanghai. Our results show that the reduction of anthropogenic SO2, NOx and NH3 would have a significant effect on the improvement of air qualitv and visibility in Shanghai.

Chemical and optical properties of aerosols and their interrelationship in winter in the megacity Shanghai of China

A field campaign on air quality was carried out in Shanghai in winter of 2012. The concentrations of NO, NO2, NOx, SO2, CO, and PM2.5increased during haze formation. The average masses of SO4^2-, NO3^-and NH4^＋were 10.3, 11.7 and 6.7 μg/m^3 during the haze episodes, which exceeded the average（9.2, 7.9, and 3.4 μg/m3） of these components in the non-haze days. The mean values for the aerosol scattering coefficient（b sp）, aerosol absorption coefficient（b ap） and single scattering albedo（SSA） were 288.7, 27.7 and0.91 Mm-1, respectively. A bi-peak distribution was observed for the mass concentrations of CO, NO, NO2, and NOx. More sulfate was produced during daytime than that in the evening due to photochemical reactions. The mass concentration of NH4＋achieved a small peak at noontime. NO3-showed lower concentrations in the afternoon and higher concentrations in the early morning. There were obvious bi-peak diurnal patterns for b sp and b ap as well as SSA. b sp and b ap showed a positive correlation with PM2.5mass concentration.（NH4）2SO4, NH4NO3, organic mass, elemental carbon and coarse mass accounted for 21.7%, 19.3%, 31.0%, 9.3% and 12.3% of the total extinction coefficient during non-haze days, and 25.6%, 24.3%, 30.1%, 8.1% and 8.2% during hazy days. Organic matter was the largest contributor to light extinction. The contribution proportions of ammonium sulfate and ammonium nitrate to light extinction were significantly higher during the hazy time than during the non-haze days.

Size-resolved effective density of submicron particles during summertime in the rural atmosphere of Beijing, China

Particle density is an important physical property of atmospheric particles. The information on high time-resolution size-resolved particle density is essential for understanding the atmospheric physical and chemical aging processes of aerosols particles. In the present study, a centrifugal particle mass analyzer （CPMA） combined with a differential mobility analyzer （DMA） was deployed to determine the size-resolved effective density of 50 to 350 nm particles at a rural site of Beijing during summer 2016. The measured particle effective densities decreased with increasing particle sizes and ranged from 1.43 to 1.55 g/cm3, on average. The effective particle density distributions were dominated by a mode peaked at around 1.5 g/cm3 for 50 to 350 nm particles. Extra modes with peaks at 1.0, 0.8, and 0.6 g/cm3 for 150, 240, and 350 nm particles, which might be freshly emitted soot particles, were observed during intensive primary emissions episodes. The particle effective densities showed a diurnal variation pattern, with higher values during daytime. A case study showed that the effective density of Aitken mode particles during the new particle formation （NPF） event decreased considerably, indicating the significant contribution of organics to new particle growth.

Do vehicular emissions dominate the source of C6–C8 aromatics in the megacity Shanghai of eastern China?

The characteristic ratios of volatile organic compounds（VOCs） to i-pentane, the indicator of vehicular emissions, were employed to apportion the vehicular and non-vehicular contributions to reactive species in urban Shanghai. Two kinds of tunnel experiments, one tunnel with more than 90% light duty gasoline vehicles and the other with more than 60% light duty diesel vehicles, were carried out to study the characteristic ratios of vehicle-related emissions from December 2009 to January 2010. Based on the experiments, the characteristic ratios of C6–C8aromatics to i-pentane of vehicular emissions were 0.53 ± 0.08（benzene）, 0.70 ± 0.12（toluene）,0.41 ± 0.09（m,p-xylenes）, 0.16 ± 0.04（o-xylene）, 0.023 ± 0.011（styrene）, and 0.15 ± 0.02（ethylbenzene）, respectively. The source apportionment results showed that around 23.3% of C6–C8 aromatics in urban Shanghai were from vehicular emissions, which meant that the non-vehicular emissions had more importance. These findings suggested that emission control of non-vehicular sources, i.e. industrial emissions, should also receive attention in addition to the control of vehicle-related emissions in Shanghai. The chemical removal of VOCs during the transport from emissions to the receptor site had a large impact on the apportionment results. Generally, the overestimation of vehicular contributions would occur when the VOC reaction rate constant with OH radicals（k OH） was larger than that of the vehicular indicator, while for species with smaller k OH than the vehicular indicator, the vehicular contribution would be underestimated by the method of characteristic ratios.

Nocturnal atmospheric chemistry of NO_(3) and N_(2)O_(5) over Changzhou in the Yangtze River Delta in China

Comprehensive observations of the nocturnal atmospheric oxidation of NO_(3)and N_(2)O_(5)were conducted at a suburban site in Changzhou in the YRD using cavity ring-down spectroscopy(CRDS)from 27 May to 24 June,2019.High concentrations of NO_(3)precursors were observed,and the nocturnal production rate of NO_(3)was determined to be 1.7±1.2 ppbv/hr.However,the nighttime NO_(3)and N_(2)O_(5)concentrations were relatively low,with maximum values of 17.7 and 304.7 pptv,respectively,illustrating the rapid loss ofNO_(3)andN_(2)O_(5).Itwas found that NO_(3)dominated the nighttime atmospheric oxidation,accounting for 50.7%,whileO3 andOH only contributed 34.1%and 15.2%,respectively.For the reactions of NO_(3)with volatile organic compounds(VOCs),styrenewas found to account for 60.3%,highlighting its dominant role in the NO_(3)reactivity.In general,the contributions of the reactions between NO_(3)and VOCs and the N_(2)O_(5)uptake to NO_(3)losswere found to be about 39.5%and 60.5%,respectively,indicating that N_(2)O_(5)uptake also played an important role in the loss of NO_(3)and N_(2)O_(5),especially under the high humidity conditions in China.The formation of nitrate at night mainly originated from N_(2)O_(5)uptake,and the maximum production rate of NO_(3)^(-)reached 6.5 ppbv/hr.The average NOx consumption rate via NO_(3)and N_(2)O_(5)chemistry was found to be 0.4 ppbv/h,accounting for 47.9%of the total NO_(x)removal.The predominant roles of NO_(3)and N_(2)O_(5)in nitrate formation and NO_(x)removal in the YRD region was highlighted in this study.

Unexpected fast radical production emerges in cool seasons:implications for ozone pollution control

Ozone is a crucial air pollutant that damages human health and vegetation.As it is related to the photo-oxidation of the nitrogen oxides and volatile organic compounds,the summertime reduction of these precursors is the primary focus of current ozone mitigation strategies.During ozone pollution episodes in eastern China,an observed accumulation of daily total oxidants(O_(x)=NO_(2)+O_(3))in cool seasons(spring and autumn:60 ppb and winter 40 ppb)is comparable to that in summer(60 ppb),indicating fast photochemical production of secondary pollutants including ozone over the year.Unrecognized fast radical primary productions are found to counteract the increased termination of hydroxyl radical and unfavorable meteorological conditions to maintain the rapid total oxidant formations in cool seasons.Elucidating and regulating the primary radical sources may be critical for the secondary air pollution control in cool seasons.