不同降水强度对PM2.5的清除作用及影响因素

云和降水过程是大气污染物的重要清除途径,但由于降水过程和大气污染颗粒物本身的复杂性,目前降水过程对大气污染物的清除机制及影响因素有待深入研究。该文利用2014年3月—2016年7月在北京地区连续观测的PM_2.5和降水数据,研究了不同降水强度对PM_2.5的清除率,以及雨滴谱、风速和降水持续时间对PM_2.5清除率的影响。研究表明:降水强度越大,对PM_2.5清除效率越高。小雨、中雨和大雨对PM_2.5清除率平均值分别为5.1%,38.5%和50.6%。小雨不但对PM_2.5的清除率最低,而且对PM_2.5的清除效果也存在很大差异,约50%的小雨个例中PM_2.5质量浓度出现减小情况,而另外50%的小雨个例中,PM_2.5质量浓度出现增加情况。在持续时间长或地面风速增大的情况下,小雨也表现出较高的清除率。在中雨和大雨情况下,PM_2.5质量浓度均出现明显减小情况。但降水持续时间和风速对中雨和大雨的清除率影响较小,这是由于中雨和大雨一般在较短时间内即可清除大部分PM_2.5,因此,对降水的持续时间和风速大小不敏感。     

Elemental composition of PM2.5 and PM10 at Mount Gongga in China during 2006

In order to investigate the chemical characteristics of atmospheric aerosols in a regional background site, PM_2.5 and PM₁₀ were collected at Mount Gongga Station once a week in 2006. The concentrations of fifteen elements including Na, Mg, Al, K, Ca, V, Fe, Ni, Cu, Zn, As, Ag, Ba, Tl, and Pb were detected by Inductively Coupled Plasma Mass Spectrometer (ICP-MS). The results showed that Na, Mg, Al, K, Ca, Fe were the major components of elements detected in PM_2.5 and PM₁₀, occupied 89.5% and 91.3% of all the elements. Crustal enrichment factor (EF) calculation indicated that several anthropogenic heavy metals (Ni, Cu, Zn, As, Ag, Tl, Pb) were transported long distances atmospherically. The concentrations of all elements (except Na) measured in PM_2.5 and PM₁₀ in spring and winter were higher than those in summer and autumn. The backward air mass trajectory analysis suggests that northeast India may be the source region of those pollutants.     

降水对江浙沪PM_(2.5)的清除效率研究

为了解不同程度的降水对江浙沪地区大气PM_(2.5)的清除作用,搜集了2014—2016年该地区41个城市的降水和PM_(2.5)观测数据,通过对比2 a非降水和全时段PM_(2.5)平均浓度的差异,发现前者显著高于后者,说明降水对该地区PM_(2.5)具有清除作用。利用降水前与降水期间PM_(2.5)的浓度差异作为降水对PM_(2.5)的清除率,降水后与降水期间的浓度差异作为雨后浓度回升的增加率,分别研究了目标区域不同时期、不同降雨量以及不同降雨时长对PM_(2.5)的清除效果。结果显示:(1)与江浙沪南部地区不同的是,北部地区降水清除率与降水前浓度存在正相关,降水后浓度的增加与当地的排放量呈正相关。(2)当降水量为30 mm或者降水时长为36 h时,清除率增幅减缓,说明降水对PM_(2.5)的清除效率存在着阈值。     

Geochemistry of regional background aerosols in the Western Mediterranean

The chemical composition of regional background aerosols, and the time variability and sources in the Western Mediterranean are interpreted in this study. To this end 2002–2007 PM speciation data from an European Supersite for Atmospheric Aerosol Research (Montseny, MSY, located 40 km NNE of Barcelona in NE Spain) were evaluated, with these data being considered representative of regional background aerosols in the Western Mediterranean Basin. The mean PM₁₀, PM_2.5 and PM₁ levels at MSY during 2002–2007 were 16, 14 and 11 µg/m³, respectively. After compiling data on regional background PM speciation from Europe to compare our data, it is evidenced that the Western Mediterranean aerosol is characterised by higher concentrations of crustal material but lower levels of OM + EC and ammonium nitrate than at central European sites. Relatively high PM_2.5 concentrations due to the transport of anthropogenic aerosols (mostly carbonaceous and sulphate) from populated coastal areas were recorded, especially during winter anticyclonic episodes and summer midday PM highs (the latter associated with the transport of the breeze and the expansion of the mixing layer). Source apportionment analyses indicated that the major contributors to PM_2.5 and PM₁₀ were secondary sulphate, secondary nitrate and crustal material, whereas the higher load of the anthropogenic component in PM_2.5 reflects the influence of regional (traffic and industrial) emissions. Levels of mineral, sulphate, sea spray and carbonaceous aerosols were higher in summer, whereas nitrate levels and Cl/Na were higher in winter. A considerably high OC/EC ratio (14 in summer, 10 in winter) was detected, which could be due to a combination of high biogenic emissions of secondary organic aerosol, SOA precursors, ozone levels and insolation, and intensive recirculation of aged air masses. Compared with more locally derived crustal geological dusts, African dust intrusions introduce relatively quartz-poor but clay mineral-rich silicate PM, with more kaolinitic clays from central North Africa in summer, and more smectitic clays from NW Africa in spring.     

Characteristics of Carbonaceous Particles in Beijing During Winter and Summer 2003

Campaigns were conducted to measure Organic Carbon (OC) and Elemental Carbon (EC) in PM2.5 during winter and summer 2003 in Beijing. Modest differences of PM2.5 and PM10 mean concentrations were observed between the winter and summer campaigns. The mean PM2.5/PM10 ratio in both seasons was around 60%, indicating PM2.5 contributed significantly to PM10. The mean concentrations of OC and EC in PM2.5 were 11.2±7.5 and 6.0±5.0μg m-3 for the winter campaign, and 9.4±2.1 and 4.3±3.0 μg m-3 for the summer campaign, respectively. Diurnal concentrations of OC and EC in PM2.5 were found high at night and low during the daytime in winter, and characterized by an obvious minimum in the summer afternoon. The mean OC/EC ratio was 1.87±0.09 for winter and Z39±0.49 for summer. The higher OC/EC ratio in summer indicates some formation of Secondary Organic Carbon (SOC). The estimated SOC was 2.8 μg m-3 for winter and 4.2μg m-3 for summer.     

Stable carbon and nitrogen isotopic characteristics of PM2.5 and PM10 in Delhi,India

This study presents the chemical composition (carbonaceous and nitrogenous components) of aerosols (PM_2.5 and PM₁₀) along with stable isotopic composition (δ¹³C and δ¹⁵N) collected during winter and the summer months of 2015–16 to explore the possible sources of aerosols in megacity Delhi, India. The mean concentrations (mean?±?standard deviation at 1σ) of PM_2.5 and PM₁₀ were 223?±?69 µg m^?3 and 328?±?65 µg m^?3, respectively during winter season whereas the mean concentrations of PM_2.5 and PM₁₀ were 147?±?22 µg m^?3 and 236?±?61 µg m^?3, respectively during summer season. The mean value of δ¹³C (range: ??26.4 to ??23.4‰) and δ¹⁵N (range: 3.3 to 14.4‰) of PM_2.5 were ??25.3?±?0.5‰ and 8.9?±?2.1‰, respectively during winter season whereas the mean value of δ¹³C (range: ??26.7 to ??25.3‰) and δ¹⁵N (range: 2.8 to 11.5‰) of PM_2.5 were ??26.1?±?0.4‰ and 6.4?±?2.5‰, respectively during the summer season. Comparison of stable C and N isotopic fingerprints of major identical sources suggested that major portion of PM_2.5 and PM₁₀ at Delhi were mainly from fossil fuel combustion (FFC), biomass burning (BB) (C-3 and C-4 type vegitation), secondary aerosols (SAs) and road dust (SD). The correlation analysis of δ¹³C with other C (OC, TC, OC/EC and OC/WSOC) components and δ¹⁵N with other N components (TN, NH₄⁺ and NO₃^?) are also support the source identification of isotopic signatures.

     

Vertical Distribution Characteristics of PM<Subscript>2.5</Subscript> Observed by a Mobile Vehicle Lidar in Tianjin,China in 2016

We present mobile vehicle lidar observations in Tianjin, China during the spring, summer, and winter of 2016. Mobile observations were carried out along the city border road of Tianjin to obtain the vertical distribution characteristics of PM_2.5. Hygroscopic growth was not considered since relative humidity was less than 60% during the observation experiments. PM_2.5 profile was obtained with the linear regression equation between the particle extinction coefficient and PM_2.5 mass concentration. In spring, the vertical distribution of PM_2.5 exhibited a hierarchical structure. In addition to a layer of particles that gathered near the ground, a portion of particles floated at 0.6–2.5-km height. In summer and winter, the fine particles basically gathered below 1 km near the ground. In spring and summer, the concentration of fine particles in the south was higher than that in the north because of the influence of south wind. In winter, the distribution of fine particles was opposite to that measured during spring and summer. High concentrations of PM_2.5 were observed in the rural areas of North Tianjin with a maximum of 350 μg m^–3 on 13 December 2016. It is shown that industrial and ship emissions in spring and summer and coal combustion in winter were the major sources of fine particles that polluted Tianjin. The results provide insights into the mechanisms of haze formation and the effects of meteorological conditions during haze–fog pollution episodes in the Tianjin area.     

Black carbon and chemical characteristics of PM<Subscript>10</Subscript> and PM<Subscript>2.5</Subscript> at an urban site of North India

The concentrations of PM₁₀, PM_2.5 and their water-soluble ionic species were determined for the samples collected during January to December, 2007 at New Delhi (28.63° N, 77.18° E), India. The annual mean PM₁₀ and PM_2.5 concentrations (± standard deviation) were about 219 (± 84) and 97 (±56) μgm⁻³ respectively, about twice the prescribed Indian National Ambient Air Quality Standards values. The monthly average ratio of PM_2.5/PM₁₀ varied between 0.18 (June) and 0.86 (February) with an annual mean of ∼0.48 (±0.2), suggesting the dominance of coarser in summer and fine size particles in winter. The difference between the concentrations of PM₁₀ and PM_2.5, is deemed as the contribution of the coarse fraction (PM_10−2.5). The analyzed coarse fractions mainly composed of secondary inorganic aerosols species (16.0 μgm⁻³, 13.07%), mineral matter (12.32 μgm⁻³, 10.06%) and salt particles (4.92 μgm⁻³, 4.02%). PM_2.5 are mainly made up of undetermined fractions (39.46 μgm⁻³, 40.9%), secondary inorganic aerosols (26.15 μgm⁻³, 27.1%), salt aerosols (22.48 μgm⁻³, 23.3%) and mineral matter (8.41 μgm⁻³, 8.7%). The black carbon aerosols concentrations measured at a nearby (∼300 m) location to aerosol sampling site, registered an annual mean of ∼14 (±12) μgm⁻³, which is significantly large compared to those observed at other locations in India. The source identifications are made for the ionic species in PM₁₀ and PM_2.5. The results are discussed by way of correlations and factor analyses. The significant correlations of Cl⁻, SO₄²⁻, K⁺, Na⁺, Ca²⁺, NO₃⁻ and Mg²⁺ with PM_2.5 on one hand and Mg²⁺ with PM₁₀ on the other suggest the dominance of anthropogenic and soil origin aerosols in Delhi.     

Variations of levels and composition of PM10 and PM2.5 at an insular site in the Western Mediterranean

The insular suburban site of Castillo de Bellver was selected for the study of the variability of PM levels and composition in the Western Mediterranean Basin (WMB).Mean annual (in 2004) PM₁₀ and PM_2.5 levels at this site were 29 and 20 µg/m³, respectively. These levels may be regarded as relatively low when compared with other suburban insular locations in the Eastern Mediterranean Basin (EMB), but they are higher than those recorded at most of the European suburban sites, especially in Northern and Western Europe. Seasonal variability of PM levels at this site is governed by meteorology rather than local emissions, whereas the daily cycles are clearly defined by the anthropogenic emissions, mainly coming from the urban area of Palma de Mallorca and the harbour area of the same city.Concerning the aerosol composition at this site, the main PM constituent is the mineral matter (29% in PM₁₀ and 16 % in PM_2.5), more than 50% (in PM₁₀) being attributable to African dust. The amount of secondary inorganic aerosols is also very high (27% in PM₁₀ and 34% in PM_2.5), with the predominance of fine ammonium sulphate, and in a less proportion fine ammonium nitrate (in winter) and coarse Ca and Na nitrate (with higher importance in summer). The carbonaceous particles, dominantly fine, account for 17% of PM₁₀ and 25% of PM_2.5. The elemental carbon/organic carbon (EC/OC) ratio reached a mean value of 0.17, similar to those observed at regional background sites in the WMB coast of Spain. The sea spray aerosols (mainly coarse) represented around 10% of PM₁₀, and only 4% in PM_2.5. Finally, the unaccounted fraction increased from 15% to 20% in PM_2.5, being mostly attributed to water.The concentrations of trace elements in PM₁₀ and PM_2.5 were usually in the range to those observed in regional background sites in the Iberian Peninsula, with the exception of the typical tracers of road traffic such as Cu, Sb, Zn, Sn and Ba, which presented concentrations in the range of urban sites of Iberia. Other elements such as Cr, Zr, Hf and Co have been identified as the main tracers of the harbour contributions.     

环北京地区空气污染指数与降水的周循环特征及其影响机制分析

部分气象要素在某些地区表现出明显的周循环特征,其位相和尺度因时因地而异.利用1980～2009年环北京地区地面常规观测气象要素资料、空气污染指数资料(简称API)及NCEP/DOE再分析资料,本文分析了环北京地区API、降水及多种气象要素的周变化特征,并对气溶胶影响降水的可能机制做了初步证明.分析表明:API表现出明显...     

有霾和无霾时宁波市大气混合层高度的日变化特征

根据2007—2013年宁波市每日8次地面观测气象资料,运用罗氏法和统计分析法计算大气混合层高度,分析其在霾日和非霾日的不同日变化特征。结果表明宁波市霾日与非霾日混合层高度均呈白天高,夜晚低的日变化特征,夏季两者差值的日变化波动最明显,波峰时间比其他季节晚3 h。混合层高度日变化趋势与风速、气温、能见度趋于一致,霾等级越重,混合层高度越低。霾日与非霾日的气温差值除冬季呈正变温外,其他季节呈负变温,冬季14时差值最小,夜间加大,春夏季凌晨差值最小,14时最大,秋季波动不明显;风速差值除冬季夜间为正值外,其余季节为负值,秋冬季差值最小、夏季最大。大气处于不稳定状态时,混合层高度随着稳定度增加而逐渐处于稳定状态时,随着稳定度增加而降低,中性大气是宁波易致霾的大气层结。霾日与非霾日大气稳定度表现不一致,中午霾日中性大气占多数,非霾日则是不稳定大气;夜间霾日稳定—弱稳定大气和中性大气所占比例相当,非霾日稳定—弱稳定大气占多数。另外,PM_(2.5)浓度在霾日和非霾日均为白天低、夜间高的日变化特征,但霾日波动大,波峰时间晚于非霾日2 h,峰值浓度也高于非霾日2.7倍;早晨或下午到上半夜是霾日的PM_(2.5)浓度两个上升时段,上午为下降时段;非霾日的两个浓度缓升(降)时段分别出现凌晨和下午(上午和前半夜)。研究成果有助于预报员了解大气混合层高度及其对霾的可能影响,从而提高霾预报预警能力。     

塔里木盆地沙尘气溶胶的柱质量密度特性

气溶胶质量密度是气溶胶重要的参数,它影响着大气中复杂的化学反应,也与气溶胶的传输过程和空间分布息息相关.基于MERRA-2再分析资料提供的气溶胶柱质量密度数据,研究了我国塔里木盆地1980—2018年长时间序列的沙尘气溶胶柱质量密度的时空分布特征.结果表明,沙尘气溶胶和沙尘PM_2.5气溶胶柱质量密度有很大的变化范围,平均值分别为0.33和0.086 g/m²,同时具有明显的年际、月和季节变化特征.沙尘气溶胶和沙尘PM_2.5气溶胶柱质量密度的年平均值在0.24~0.41和0.06~0.11 g/m²范围内变化;春季最大,其平均值分别为0.47和0.12 g/m²,冬季最小,其平均值分别为0.13和0.04 g/m²;月平均值最大出现在5月,分别为0.57和0.14 g/m²,最小在1月,分别为0.1和0.03 g/m².     

基于国际大气化学—气候模式比较计划模式数据评估未来气候变化对中国东部气溶胶浓度的影响

气候变化引起的地面气溶胶浓度变化与区域空气质量密切相关。本文利用“国际大气化学—气候模式比较计划”（Atmospheric Chemistry and Climate Model Intercomparison Project, ACCMIP）中4个模式的试验数据分析了RCP8.5情景下2000~2100年气候变化对中国气溶胶浓度的影响。结果显示,在人为气溶胶排放固定在2000年、仅考虑气候变化的影响时,2000~2100年气候变化导致中国北部地区（31°N~45°N, 105°E~122°E）硫酸盐、有机碳和黑碳气溶胶分别增加28%、21%和9%,硝酸盐气溶胶在中国东部地区减少30%。气候变化对细颗粒物（PM_2.5）浓度的影响有显著的季节变化特征,冬季PM_2.5浓度在中国东部减少15%,这主要是由硝酸盐气溶胶在冬季的显著减少造成的;夏季PM_2.5浓度在中国北部地区增加16%,而长江以南地区减少为9%,这可能与模式模拟的未来东亚夏季风环流的增强有关。     

Impacts of ENSO on wintertime PM2.5 pollution over China during 2014–2021

China has implemented a series of emission reduction policies since 2013, and the concentration of air pollutants has consequently decreased significantly. However, PM_2.5 (particulate matter with an aerodynamic diameter less than 2.5 µm) pollution still occurs in China in relation to the interannual variations in meteorological conditions. Considering that El Niño–Southern Oscillation (ENSO) is the strongest signal modulating the interannual variation in the atmosphere–ocean system, in this study the authors investigate the variations in PM_2.5 concentrations in four megacity clusters of China during the winter season associated with four individual ENSO events from 2014 to 2021. Results show that the wintertime PM_2.5 concentrations in the Beijing–Tianjin–Hebei and Fenwei Plain regions during El Niño years are higher than those during La Niña years, which can be explained by the anomalous southerly (northerly) winds during El Niño (La Niña) favoring PM_2.5 accumulation (diffusion). In the Pearl River Delta region, PM_2.5 concentrations decrease in El Niño relative to La Niña years owing to the enhanced water vapor flux and precipitation, removing more PM_2.5 from the atmosphere. The comprehensive effects of wind and precipitation anomalies lead to the unpredictability of the impacts of ENSO on PM_2.5 over the Yangtze River Delta region, which should be analyzed case by case.摘要2013年以来中国实施了一系列减排政策, 大气污染物浓度明显下降, 但由于气象条件的年际变化, 中国PM_2.5 (空气动力学直径小于2.5 µm的颗粒物) 污染仍然存在. 厄尔尼诺–南方涛动 (ENSO) 是调节大气–海洋系统年际变化的最强信号. 本文研究了2014–2021年四次ENSO事件期间, 中国四个特大城市群冬季PM_2.5浓度的变化. 结果表明, 在京津冀和汾渭平原地区, 由于厄尔尼诺 (拉尼娜) 期间的偏南风 (偏北风) 异常有利于 PM_2.5 的积累 (扩散), 冬季PM_2.5浓度在厄尔尼诺年高于拉尼娜年. 在珠三角地区, 由于厄尔尼诺冬季水汽通量和降水的增加有利于大气中PM_2.5的湿清除, 冬季PM_2.5浓度在厄尔尼诺年低于拉尼娜年. 在环流和降水异常的综合作用下, ENSO对长三角地区PM_2.5浓度的影响难以预测, 应逐案分析.     

安徽省大气污染物浓度的周循环特征评估

大气质量的周循环特征反映了人类周期性的活动规律对大气环境的影响。基于安徽省16个城市PM_(2.5)、PM_(10)、CO、NO_2、SO_2和O_3这6种污染物的监测结果,对安徽省大气污染的周循环特征进行了评估。首先基于原始逐小时污染物浓度时间序列在日和周窗口时间宽度上的滑动平均序列,定义了周循环距平百分率序列的计算方法,排除了日循环和长期低频变化的影响。以此为基础,基于合成分析以及贝叶斯统计分析,发现这6种大气污染物中,PM_(2.5)、PM_(10)、CO和NO_2有着较为明显的周循环变化特征,其周循环距平百分率有着较大的变幅;而O_3的周循环特征相对不明显。主成分分析获得的周循环,第1模态发现除O_3以外的其他5种污染物的周循环有着同样的演进模式,即从周三开始持续到周五的累积和周六之后的衰减;O_3的周循环峰值与谷值与其他污染物存在着大于12 h的滞后,反映了在周循环尺度上O_3距平变化对其光化学反应前体距平变化的滞后响应特征。     

Chemical characterization of water-soluble aerosols in different residential environments of semi aridregion of India

This paper deals with the atmospheric concentrations of PM₅ and PM_2.5 particulate matter and its water soluble constituents along with the size distribution of ions and spatial variation at three different residential environments in a semiarid region in India. Samples were collected from the indoors and outdoors of urban, rural and roadside sites of Agra during October 2007–March 2008. The mean concentrations of PM_2.5 indoors and outdoors were 178 μgm⁻³ and 195 μgm⁻³ while the mean concentrations of PM₅ indoors and outdoors were 231.8 μgm⁻³ and 265.2 μgm⁻³ respectively. Out of the total aerosol mass, water soluble constituents contributed an average of 80% (33% anions, 50% cations) in PM₅ and 70% (29% anions, 43% cations) in PM_2.5. The indoor–outdoor ratio of water soluble components suggested additional aerosol indoor sources at rural and roadside sites. Indoor–outdoor correlations were also determined which show poor relationships among concentrations of aerosol ions at all three sites. Univariate Pearson correlation coefficients among water soluble aerosols were determined to evaluate the relationship between aerosol ions in indoor and outdoor air.     

中国主要城市群在灰霾污染下的近地面风场特征

利用2015—2016年全国PM_(2.5)质量浓度站点资料及CCMP(Cross Calibrated Multi-Platform)风场再分析资料,对中国华北、长三角、珠三角以及四川盆地主要城市在PM_(2.5)污染下的近地面风场及其影响进行统计分析。结果表明:(1)近地面风速与PM_(2.5)质量浓度表现为负相关,低风速有利于PM_(2.5)的积累,但是该相关关系并不完全显著,体现出"冬强夏弱"的季节性差异;(2)不同地区PM_(2.5)质量浓度对不同风向的反应不同,华北地区在偏南风主导下PM_(2.5)质量浓度较高,长三角则是在偏西风主导下PM_(2.5)质量浓度较高,而珠三角地区冬季PM_(2.5)质量浓度较高,主导风向为偏北风;(3)通过分析地面散度场发现不同地区主导的污染类型不同,华北地区、长三角以及珠三角污染类型主要为区域性污染,四川盆地主要为局地型污染。     

Influences of meteorological conditions on interannual variations of particulate matter pollution during winter in the Beijing–Tianjin–Hebei area

To investigate the interannual variations of particulate matter (PM) pollution in winter, this paper examines the pollution characteristics of PM with aerodynamic diameters of less than 2.5 and 10 μm (i.e., PM_2.5 and PM₁₀), and their relationship to meteorological conditions over the Beijing municipality, Tianjin municipality, and Hebei Province—an area called Jing–Jin–Ji (JJJ, hereinafter)—in December 2013–16. The meteorological conditions during this period are also analyzed. The regional average concentrations of PM_2.5 (PM₁₀) over the JJJ area during this period were 148.6 (236.4), 100.1 (166.4), 140.5 (204.5), and 141.7 (203.1) μg m^–3, respectively. The high occurrence frequencies of cold air outbreaks, a strong Siberian high, high wind speeds and boundary layer height, and low temperature and relative humidity, were direct meteorological causes of the low PM concentration in December 2014. A combined analysis of PM pollution and meteorological conditions implied that control measures have resulted in an effective improvement in air quality. Using the same emissions inventory in December 2013–16, a modeling analysis showed emissions of PM_2.5 to decrease by 12.7%, 8.6%, and 8.3% in December 2014, 2015, and 2016, respectively, each compared with the previous year, over the JJJ area.     

Relative contributions of boundary-layer meteorological factors to the explosive growth of PM<Subscript>2.5</Subscript> during the red-alert heavy pollution episodes in Beijing in December 2016

Based on observations of urban mass concentration of fine particulate matter smaller than 2.5 μm in diameter (PM_2.5), ground meteorological data, vertical measurements of winds, temperature, and relative humidity (RH), and ECMWF reanalysis data, the major changes in the vertical structures of meteorological factors in the boundary layer (BL) during the heavy aerosol pollution episodes (HPEs) that occurred in winter 2016 in the urban Beijing area were analyzed. The HPEs are divided into two stages: the transport of pollutants under prevailing southerly winds, known as the transport stage (TS), and the PM_2.5 explosive growth and pollution accumulation period characterized by a temperature inversion with low winds and high RH in the lower BL, known as the cumulative stage (CS). During the TS, a surface high lies south of Beijing, and pollutants are transported northwards. During the CS, a stable BL forms and is characterized by weak winds, temperature inversion, and moisture accumulation. Stable atmospheric stratification featured with light/calm winds and accumulated moisture (RH > 80%) below 250 m at the beginning of the CS is closely associated with the inversion, which is strengthened by the considerable decrease in near-surface air temperature due to the interaction between aerosols and radiation after the aerosol pollution occurs. A significant increase in the PLAM (Parameter Linking Aerosol Pollution and Meteorological Elements) index is found, which is linearly related to PM mass change. During the first 10 h of the CS, the more stable BL contributes approximately 84% of the explosive growth of PM_2.5 mass. Additional accumulated near-surface moisture caused by the ground temperature decrease, weak turbulent diffusion, low BL height, and inhibited vertical mixing of water vapor is conducive to the secondary aerosol formation through chemical reactions, including liquid phase and heterogeneous reactions, which further increases the PM_2.5 concentration levels. The contribution of these reaction mechanisms to the explosive growth of PM_2.5 mass during the early CS and subsequent pollution accumulation requires further investigation.     

Concentrations of metallic elements in long-range-transported aerosols measured simultaneously at three coastal sites in China and Japan

To determine the effects of long-range transport of aerosols from an upwind area in East Asia to a downwind area in Japan, we chemically analyzed aerosols collected simultaneously on Tuoji Island (Shandong Province, China), Fukue Island (Nagasaki Prefecture, Japan), and Cape Hedo (Okinawa Prefecture, Japan). We focused on changes in the metallic composition of PM_2.5 aerosols during long-range transport. The average mass concentrations of PM_2.5 at the three sites decreased in the order Tuoji Island > Fukue Island ≈ Cape Hedo (48.3 ± 4.5, 13.9 ± 1.5, and 13.2 ± 0.9 μg/m³, respectively). The fraction of coarse particles in total suspended particles estimated by (1–PM_2.5/TSP) was highest on Cape Hedo, indicating that the contribution of sea salts was increased by long-range transport of the aerosols over the ocean. Enrichment factor analysis revealed that at all three sites, Al, K, Ca, Mn, Fe, Co, Sr, and Ba originated from soil; whereas Cr, Ni, Cu, Zn, As, Mo, Ag, Cd, Sn, Sb, Tl, and P appeared to be of anthropogenic origin. Na was the most abundant element on Cape Hedo, indicating the addition of sea salts during aerosol transport. The V concentration was highest at Fukue Island, which was ascribed to V emission from ships. Sixty-one percent of the V on Fukue Island and 62% of the V on Cape Hedo were determined to have originated from ships, implicating of data obtained on dates during which backward trajectory analysis indicated that the same air mass passed over Tuoji Island, Fukue Island, and Cape Hedo in that order.