Particulate matter trends and quantification of the spring sand-dust contribution in Hohhot,Inner Mongolia,from 2013 to 2017

On 10 September 2013,the State Council promulgated the Action Plan for the Prevention and Control of Air Pollution(hereinafter referred to as the Action Plan).To study the variations in the air pollutant concentrations in Hohhot during the implementation of the Action Plan and the effects of various measures,the daily concentrations of air pollutants(fine particulate matter(PM_(2.5)),inhalable PM(PM 10),SO_(2),and NO_(2))in Hohhot published by the China Environmental Monitoring Station were obtained to analyze the general meteorological conditions in Inner Mongolia from 2013 to 2017.The variations and causes of the ambient PM concentration in Hohhot were examined,and the quantitative influence of sandstorms on the ambient PM concentration in Hohhot was analyzed by selecting the spring season with frequent sandstorms as an example.The results showed the following.(1)The air quality in Hohhot continuously improved,and compared with those in 2013,the PM_(2.5)and PM 10 concentrations decreased by 24.6%and 48.2%,respectively,in 2017.However,the air pollutant concentrations remained high,with the average PM_(2.5)and PM 10 concentrations exceeding the national secondary standards by 22.9%and 35.7%,respectively.(2)The reductions in the spring PM_(2.5)and PM 10 concentrations were 5.6%and 8.9%,respectively,and the annual decreases in the PM_(2.5)and PM 10 concentrations were 3.6 and 15.1μg m^(−3)yr−1,respectively,from 2013 to 2017.(3)The absolute contribution ranges of dust weather to the concentrations of PM_(2.5),PM 10,and TSP during 2013–17 were 0.6–5.2μg m^(−3),9.0–16.9μg m^(−3),and 14.7–30.0μg m^(−3),respectively,in Hohhot during the spring.

Comparative research on visibility and light extinction of PM_(2.5)components during 2014–17 in the North China plain

Severe air pollution with visibility deterioration has long been a focus in the North China Plain(NCP).In this study,concentration and light extinction analysis of PM_(2.5)chemical components were carried out from 2014 to 2017 to study the pollution characteristics in Baoding,a case city of the NCP.The annual average concentration of total PM_(2.5)components showed a declining trend,decreasing by 11μg m^(−3)(water-soluble inorganic ions),23μg m^(−3)(carbonaceous aerosols),and 1796 ng m^(−3)(inorganic elements).Contributing 82.9%to the concentration of total ions,the dominant components,NH 4+,NO 3−,and SO_(4)^(2−)became the main pollutants in PM_(2.5)pollution.Based on the IMPROVE algorithm,the average reconstructed PM_(2.5)mass concentration was 93±69μg m^(−3)during the observation period.Meanwhile,the light extinction coefficients were 373.8±233.6 M^(m−1),405.3±300.1M^(m−1),554.3±378.2M^(m−1)and 1005.2±750.3M^(m−1),in spring,summer,autumn,and winter,respectively.Ammonium sulfate,ammonium nitrate,and organic matter were the largest contributors to light extinction,accounting for a total of 55%–77%in the four seasons.The b sca(light scattering by particles and gases)reconstructed from PM_(2.5)components(Rb_(sca))and the b sca converted from visibility(Vb_(sca))were compared to evaluate the performance of the IMPROVE algorithm,revealing a high correlation coefficient of 0.84.The high values of Vb_(sca)were underestimated while the low values were overestimated,as determined through comparison with the one-to-ne line.Especially,when Rb_(sca)>1123M^(m−1)(corresponding to<2.0 km,approximately),Vb_(sca)was underestimated by 17.6%.PM_(2.5)mass concentration and relative humidity also had an impact on the estimation.

Trends in particulate matter and its chemical compositions in China from 2013–2017

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 PM2.5 in 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 Pollution from 2013-2017.The results show the following.(1)The particulate matter mass concentration in China showed a significant downward trend;however,the PM2.5 annual mass concentration in 64%of cities exceeds the New Chinese Ambient Air Quality Standard(CAAQS)GradeⅡ(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 PM2.5 concentration 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 PM2.5 decreased 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 PM2.5 chemical 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-,NO3-,and NH4+decreased with the decrease of the particulate matter mass concentration in different particle size fractions.The fine-particle size peaks of SO42-,NO3-and NH4+shifted from 0.65-1.1μm to the finer size range of0.43-0.65μm during the same time frame.

Evolution of boundary layer ozone in Shijiazhuang,a suburban site on the North China Plain

The structure of the boundary layer affects the evolution of ozone(O3), and research into this structure will provide important insights for understanding photochemical pollution.In this study, we conducted a one-month observation(from June 15 to July 14, 2016) of the boundary layer meteorological factors as well as O3 and its precursors in Luancheng County,Shijiazhuang(37°53′N, 114°38′E). Our research showed that photochemical pollution in Shijiazhuang is serious, and the mean hourly maximum and mean 8-hr maximum O3 concentrations are 97.9 ± 26.1 and 84.4 ± 22.4 ppbV, respectively. Meteorological factors play a significant role in the formation of O3. High temperatures and southeasterly winds lead to elevated O3 values, and at moderate relative humidity(40%–50%) and medium boundary layer heights(1200–1500 m), O3 production sensitivity occurred in the transitional region between volatile organic compounds(VOC) and nitrogen oxides(NOx) limitations,and the O3 concentration was the highest. The vertical profiles of O3 were also measured by a tethered balloon. The results showed that a large amount of O3 was stored in the residual layer, and the concentration was positively correlated with the O3 concentration measured the previous day. During the daytime of the following day, the contribution of O3 stored in the residual layer to the boundary layer reached 27%± 7% on average.

Characteristics of PM_(2.5) pollution in Beijing after the improvement of air quality

Following the implementation of the strictest clean air policies to date in Beijing,the physicochemical characteristics and sources of PM_(2.5) have changed over the past few years.To improve pollution reduction policies and subsequent air quality further,it is necessary to explore the changes in PM_(2.5) over time.In this study,over one year(2017-2018)field study based on filter sampling(TH-150C;Wuhan Tianhong,China)was conducted in Fengtai District,Beijing,revealed that the annual average PM_(2.5) concentration(64.8±43.1μg/m^3)was significantly lower than in previous years and the highest PM_(2.5) concentration occurred in spring(84.4±59.9μg/m^3).Secondary nitrate was the largest source and accounted for 25.7%of the measured PM_(2.5).Vehicular emission,the second largest source(17.6%),deserves more attention when considering the increase in the number of motor vehicles and its contribution to gaseous pollutants.In addition,the contribution from coal combustion to PM_(2.5) decreased significantly.During weekends,the contribution from EC and NO3−increased whereas the contributions from SO4^2−,OM,and trace elements decreased,compared with weekdays.During the period of residential heating,PM_(2.5) mass decreased by 23.1%,compared with non-heating period,while the contributions from coal combustion and vehicular emission,and related species increased.With the aggravation of pollution,the contribution of vehicular emission and secondary sulfate increased and then decreased,while the contribution of NO3−and secondary nitrate continued to increase,and accounted for 34.0%and 57.5%of the PM_(2.5) during the heavily polluted days,respectively.

Characterization and source identification of submicron aerosol dur ing ser ious haze pollution periods in Beijing

Submicron aerosol is of extensive concern not only due to its significant impact on air quality but also because it is detrimental to human health.In this study,we investigated the characteristics,sources and chemical processes of submicron aerosol based on realtime online measurements of submicron aerosols(NR-PM 1)during December 2015 at an urban site in Beijing.The average mass concentration of NR-PM 1 was 92.5±84.9μg/m^(3),the hourly maximum was 459.1μg/m^(3) during the entire observation.The organic aerosol(OA)(55%)was the largest contributor to NR-PM 1.The average mass concentration of PAHs was 0.217±0.247μg/m^(3),exhibiting the highest concentration at night and the lowest levels in the daytime.The average mass concentration of organic nitrate was 2.52±2.36μg/m^(3) and that of inorganic nitrate was 7.62±8.22μg/m^(3),accounting for 36%and 64%,respectively,of the total nitrate mass.Positive matrix factorization(PMF)differentiated the OA into five chemical components including LV-OOA,SV-OOA,COA,HOA and CCOA,accounting for 22%,16%,13%,25%and 24%respectively,of the total OA.The average NR-PM 1 mass concentration on the heavy polluted days(HPD)was 182.8±70.2μg/m^(3),which was approximately 9 times that on clean days(CD).The enhanced secondary formation of SNA was evident on HPD,especially the rapid increase of sulfate(23%)and nitrate(19%).

Assessment of health benefit of PM_(2.5) reduction during COVID-19 lockdown in China and separating contributions from anthropogenic emissions and meteorology

The national lockdown policies have drastically disrupted socioeconomic activities during the COVID-19 pandemic in China,which provides a unique opportunity to investigate the air quality response to such anthropogenic disruptions.And it is meaningful to evaluate the potential health impacts of air quality changes during the lockdown,especially for PM_(2.5) with adverse health effects.In this study,by using PM_(2.5) observations from 1388 monitor-ing stations nationwide in China,we examine the PM_(2.5) variations between the COVID-19 lockdown(February and March in 2020)and the same period in 2015-2019,and find that the national average of PM_(2.5) decreases by 18 μg/m^(3),and mean PM_(2.5) for most sites(about 75%)decrease by 30%-60%.The anthropogenic and meteorological contributions to these PM_(2.5) variations are also determined by using a stepwise multiple linear regression(MLR)model combined with the Kolmogorov-Zurbenko filter.Our results show that the change of anthropogenic emissions is a leading contributor to those widespread PM_(2.5) reductions,and meteorological conditions have the negative influence on PM_(2.5) reductions for some re-gions,such as Beijing-Tianjin-Hebei(BTH).Additionally,the avoided premature death due to PM_(2.5) reduction is estimated as a predicted number based on a log-linear concentration-response function.The total avoided premature death is 9952 in China,with dominant con-tribution(94%)from anthropogenic emission changes.For BTH,Yangtze River Delta,Pearl River Delta and Hubei regions,the reductions of PM_(2.5) are 24.1,24.3,13.5 and 29.5 μg/m^(3),with the avoided premature deaths of 1066,1963,454 and 583,respectively.