Determination of levoglucosan and its isomers in size fractions of aerosol standard reference materials

The present study tested the extraction efficiency and quantification reproducibility of anhydrosugars in a series of NIST SRMs using two extraction protocols and isotopically-labeled (d₇-levoglucosan) vs. chemically analogous (sedoheptulosan) surrogates. In both instances, levoglucosan concentrations in the different versions of the Washington, D.C. urban dust standard (SRM 1649, 1649a, 1649b, and RM 8785) were similar. The present test also showed that levoglucosan concentrations were not affected by long-term shelf storage of dry material. Variability of analyses were similar for both surrogates and averaged <5%. Surrogate recoveries were shown to average 103 ± 7% and 97 ± 7% for d₇-levoglucosan and sedoheptulosan, respectively. The choice of solvent was shown to affect recoveries the most (but not variability). Levoglucosan concentrations were either seriously underestimated or overestimated with ethyl acetate extraction when d₇-levoglucosan or sedoheptulosan was used as surrogate, respectively. These results point to the need to use some fraction of polar solvent (i.e. methanol) in the solvent mixture. Anhydrosugar concentrations in the urban dust from the Czech Republic (candidate SRMs 2786 and 2787) were characterized by 3- to 7-fold higher anhydrosugar concentrations than those observed in the Washington, D.C. urban dust. The internal anhydrosugar signatures (i.e. levoglucosan/mannosan ratio: L/M) confirm the predominance of biomass combustion sources in both SRM series with mixed inputs from hardwood and softwood combustion in the Washington, D.C. urban dust and a predominantly softwood source in the Prague urban dust. The uniform distribution of anhydrosugars, across the particle size distribution of both SRM series, confirms earlier studies that low temperature charred materials contribute significant inputs to atmospheric ultrafine particles with long atmospheric residence time and transport ranges.     

重庆主城区大气重污染形势的激光雷达探测与分析

2013年1月12日-26日,利用大气超级站ALS300型激光雷达对重庆主城区大气进行了连续探测,分析了重污染形势期间的大气扩散条件及大气颗粒物时空分布等探测结果。分析表明,大气层结持续稳定,扩散条件差使得大气颗粒物浓度居高不下,大气能见度持续恶化;大气重污染期间PBL高度较低,平均为320～350m;大气颗粒物污染带处于100～400m高度范围;全国范围内异常的大气环流形势和重庆主城区独特的地形、气候特征是造成持续大气重污染形势的原因。     

MAX-DOAS observation in the midlatitude marine boundary layer: Influences of typhoon forced air mass

As a passive remote sensing technique, MAX-DOAS method was widely used to investigate the vertical profiles of aerosol and trace gases in the lower troposphere. However, the measurements for midlatitude marine boundary layer are rarely reported, especially during the storm weather system. In this study, the MAX-DOAS was used to retrieve the aerosol, HCHO and NO₂ vertical distribution at Huaniao Island of East China Sea in summer 2018, during which a strong tropical cyclone developed and passed through the measurement site. The observed aerosol optical depth (AOD), HCHO- and NO_2-VCDs (Vertical Column Density) were in the range of 0.19-0.97, (2.57-12.27) × 10¹⁵ molec/cm², (1.24-4.71) × 10¹⁵ molec/cm², which is much higher than remote ocean area due to the short distance to continent. The vertically resolved aerosol extinction coefficient (AEC), HCHO and NO₂ presented the decline trend with the increase of height. After the typhoon passing through, the distribution of high levels of aerosol and HCHO stretched to about 1 km and the abundances of the bottom layer were found as double higher than before, reaching 0.51 km⁻¹ and 2.44 ppbv, while NO₂ was still constrained within about 300 m with 2.59 ppbv in the bottom layer. The impacts of typhoon process forced air mass were also observed at the suburban site in Shanghai in view of both the aerosol extinction and chemical components. The different changes on air quality associated with typhoon and its mechanism in two different environments: coastal island and coastal city are worthy of further investigation as it frequent occurred in East Asia during summer and fall.     

四川省气溶胶光学厚度时空分布特征

本文利用MODIS气溶胶光学厚度产品,建立了气溶胶光学厚度与PM10/2.5的线性关系。分析了2008年~2012年四川省的气溶胶光学厚度时空分布特征,以成都市为特例分析了2003年~2012年的气溶胶光学厚度时空分布。结果显示:气溶胶光学厚度与PM10/2.5的线性关系较高;川西高原具有较低的气溶胶光学厚度,康定、马尔康、西昌、雅安等地年均气溶胶光学厚度约0.2;四川盆地区域具有较高的气溶胶光学厚度,以成都、德阳等地为代表,年均值在0.8~1.0之间,并具有明显季节变化特征;成都市的气溶胶光学厚度时空分布具有明显的城市特点。这些时空分布的特征与四川省的工业情况、地理位置、气候条件有关。     

2018年中国长江三角洲地区气溶胶的垂直分布特征

利用主动式遥感卫星云-气溶胶激光雷达和红外探测者卫星观测(CALIPSO)提供的激光雷达资料,重点分析了2017-12～2018-11中国长江三角洲地区对流层大气中532 nm气溶胶消光系数,气溶胶退偏比,气溶胶色比以及各类型气溶胶的时空变化特征.对气溶胶的光学参数随高度变化的研究表明,与对流层高空相比,一般在对流层低空中气溶胶消光能力更强,气溶胶粒子更规则,气溶胶粒径更小.对气溶胶的光学参数随季节变化的研究表明,与冬春季相比,一般夏秋季在对流层高空中气溶胶消光能力更强,在2 km以下气溶胶粒子更规则,在对流层高空中气溶胶粒径的范围更大.长江三角洲地区全年中污染沙尘气溶胶出现的频率最高,为37. 481 6%,夏秋季烟尘、污染大陆与洁净海洋气溶胶出现的频率比冬春季高,而夏秋季沙漠沙尘气溶胶出现的频率相对较低.     

冷高压影响下高层水平输送对珠海市三维臭氧浓度分布的影响分析

采用地基激光雷达系统测量了近地层臭氧、气溶胶消光系数和风场的垂直分布,研究了2021年11月一次典型臭氧污染过程的时空分布特征.11月16日—17日,在弱冷高压脊天气型下,以下沉气流为主,天气晴好,有利于臭氧生成,在下沉气流主导下,高层气团输送对污染物的分布起决定性作用.其中700 m高度以上气团来源是影响16日与17日臭氧浓度峰值出现时间的重要因子,当该高度气团来自洁净海面时,造成珠海臭氧污染的主要是低层深圳输送的臭氧,臭氧往往停留在珠江口,由夜间海风输送到珠海,污染发生的时间在傍晚,持续到夜间消散;而当该高度气团与低层一样来自于深圳、东莞时,各个高度的气团均携带上游城市生成的污染物,可在下沉气流的作用下直接达到地面,造成污染,污染发生的时间在午后,在本研究中由于下沉气流加强,进一步加强了海陆风,从而使臭氧在17日傍晚得到很好的清除.     

Vertical aerosol data assimilation technology and application based on satellite and ground lidar: A review and outlook

Observations and numerical models are mainly used to investigate the spatiotemporal distribution and vertical structure characteristics of aerosols to understand aerosol pollution and its effects. However, the limitations of observations and the uncertainties of numerical models bias aerosol calculations and predictions. Data assimilation combines observations and numerical models to improve the accuracy of the initial, analytical fields of models and promote the development of atmospheric aerosol pollution research. Numerous studies have been conducted to integrate multi-source data, such as aerosol optical depth and aerosol extinction coefficient profile, into various chemical transport models using various data assimilation algorithms and have achieved good assimilation results. The definition of data assimilation and the main algorithms will be briefly presented, and the progress of aerosol assimilation according to two types of aerosol data, namely, aerosol optical depth and extinction coefficient, will be presented. The application of vertical aerosol data assimilation, as well as the future trends and challenges of aerosol data assimilation, will be further analysed.     

Evaluation of the influence of El Niño–Southern Oscillation on air quality in southern China from long-term historical observations

•Strong ENSO influence on AOD is found in southern China region. •Low AOD occurs in El Niño but high AOD occurs in La Niña events in southern China. •Angstrom exponent anomalies reveals the circulation pattern during each ENSO phase. •ENSO exerts large influence (70.5%) on annual variations of AOD during 2002–2020. •Change of anthropogenic emissions is the dominant driver for AOD trend (2002–2020). Previous studies demonstrated that the El Niño–Southern Oscillation (ENSO) could modulate regional climate thus influencing air quality in the low-middle latitude regions like southern China. However, such influence has not been well evaluated at a long-term historical scale. To filling the gap, this study investigated two-decade (2002 to 2020) aerosol concentration and particle size in southern China during the whole dynamic development of ENSO phases. Results suggest strong positive correlations between aerosol optical depth (AOD) and ENSO phases, as low AOD occurred during El Niño while high AOD occurred during La Niña event. Such correlations are mainly attributed to the variation of atmospheric circulation and precipitation during corresponding ENSO phase. Analysis of the angstrom exponent (AE) anomalies further confirmed the circulation pattern, as negative AE anomalies is pronounced in El Niño indicating the enhanced transport of sea salt aerosols from the South China Sea, while the La Niña event exhibits positive AE anomalies which can be attributed to the enhanced import of northern fine anthropogenic aerosols. This study further quantified the AOD variation attributed to changes in ENSO phases and anthropogenic emissions. Results suggest that the long-term AOD variation from 2002 to 2020 in southern China is mostly driven (by 64.2%) by the change of anthropogenic emissions from 2002 to 2020. However, the ENSO presents dominant influence (70.5%) on year-to-year variations of AOD during 2002–2020, implying the importance of ENSO on varying aerosol concentration in a short-term period.     

影响北仑区域能见度的因素研究

利用对北仑区域内的气溶胶散射系数、气溶胶浓度、黑炭浓度以及NO2浓度的监测和分析,对区域影响能见度的的因素进行了研究,研究结果表明,影响能见度的消光系数主要由气溶胶的散射、气溶胶的吸收,干洁大气的散射和气态污染物的吸收四项组成,且组成比例总体稳定,但是,不同空气质量级别和灰霾天与非灰霾天之间的消光系数值及组成差异较大;通过对气溶胶与光散射系数的拟合得到,两者存在较好的正相关性。     

A Geospatial Methodology to Identify Locations of Concentrated Runoff from Agricultural Fields

A geospatial methodology has been developed that utilizes high resolution lidar‐derived DEMs to help track runoff from agricultural fields and identify areas of potential concentrated flow through vegetated riparian areas in the Coastal Plain of Virginia. Points of concentrated flow are identified across 74 agricultural fields within the Virginia portion of the Chesapeake Bay watershed. On average, 70% of the surface area of the agricultural fields analyzed drains through less than 20 m of the field margin, and on average 81% of the field surface area drains through 1% or less of the field margin. Within the riparian buffer, locations that were predicted by the geospatial model to have high levels of concentrated flow were found to exhibit evidence of channelization. Results indicate that flow concentration and channelized flow through vegetated riparian areas may be common along the margin of agricultural fields, resulting in vegetated riparian areas that are less effective at sediment trapping than assumed. Additional results suggest that the regulations governing the location and width of vegetated riparian may not be sufficient to achieve goals for reducing sediment and nutrient runoff from nonpoint agricultural sources. Combined with the increasing availability of lidar‐derived DEMs, the geospatial model presented has the potential to advance management practices aimed at reducing nonpoint source pollution leaving agricultural fields.