Spatiotemporal trends of PM2.5 and its major chemical components at urban sites in Canada

To evaluate the effectiveness of emission control regulations designed for reducing air pollution, chemically resolved PM_2.5 data have been collected across Canada through the National Air Pollution Surveillance network in the past decade. 24-hr time integrated PM_2.5 collected at seven urban and two rural sites during 2010-2016 were analyzed to characterize geographical and seasonal patterns and associated potential causes. Site-specific seven-year mean gravimetric PM_2.5 mass concentrations ranged from 5.7 to 9.6 µg/m³. Seven-year mean concentrations of SO₄^2?, NO₃^?, NH₄⁺, organic carbon (OC), and elemental carbon (EC) were in the range of 0.68 to 1.6, 0.21 to 1.5, 0.27 to 0.71, 1.1 to 1.9, and 0.37 to 0.71 µg /m³, accounting for 10.8%-18.1%, 3.7%-16.7%, 4.7%-7.4%, 18.4%-21.0%, and 6.4%-10.6%, respectively, of gravimetric PM_2.5 mass. PM_2.5 and its five major chemical components showed higher concentrations in southeastern Canada and lower values in Atlantic Canada, with the seven-year mean ratios between the two regions being on the order of 1.7 for PM_2.5 and 1.8-7.1 for its chemical components. When comparing the concentrations between urban and rural sites within the same region, those of SO₄^2? and NH₄⁺ were comparable, while those of NO₃^?, OC, and EC were around 20%, 40%-50%, and 70%-80%, respectively, higher at urban than rural sites, indicating the regional scale impacts of SO₄^2? and NH₄⁺ and effects of local sources on OC and EC. Monthly variations generally showed summertime peaks for SO₄^2? and wintertime peaks for NO₃^?, but those of NH₄⁺, OC, and EC exhibited different seasonality at different locations.     

Aerosol transmission,an indispensable route of COVID-19 spread: case study of a department-store cluster

• Aerosol transmission is an indispensable route of COVID-19 spread. • Different outbreak sites have different epidemiologic feature. • SRAS-CoV-2 can exist for a long time in aerosol. • SRAS-CoV-2 RNA can be detected in aerosol in diverse places. • Some environmental factors can impact SARS-CoV-2 transportation in aerosol. Patients with COVID-19 have revealed a massive outbreak around the world, leading to widespread concerns in global scope. Figuring out the transmission route of COVID-19 is necessary to control further spread. We analyzed the data of 43 patients in Baodi Department Store (China) to supplement the transmission route and epidemiological characteristics of COVID-19 in a cluster outbreak. Incubation median was estimated to endure 5.95 days (2–13 days). Almost 76.3% of patients sought medical attention immediately upon illness onset. The median period of illness onset to hospitalization and confirmation were 3.96 days (0–14) and 5.58 days (1–21), respectively. Patients with different cluster case could demonstrate unique epidemiological characteristics due to the particularity of outbreak sites. SRAS-CoV-2 can be released into the surrounding air through patient’s respiratory tract activities, and can exist for a long time for long-distance transportation. SRAS-CoV-2 RNA can be detected in aerosol in different sites, including isolation ward, general ward, outdoor, toilet, hallway, and crowded public area. Environmental factors influencing were analyzed and indicated that the SARS-CoV-2 transportation in aerosol was dependent on temperature, air humidity, ventilation rate and inactivating chemicals (ozone) content. As for the infection route of case numbers 2 to 6, 10, 13, 16, 17, 18, 20 and 23, we believe that aerosol transmission played a significant role in analyzing their exposure history and environmental conditions in Baodi Department Store. Aerosol transmission could occur in some cluster cases when the environmental factors are suitable, and it is an indispensable route of COVID-19 spread.     

全球沙尘气溶胶源汇分布及其变化特征的模拟分析

根据全球沙尘气溶胶气候模式GEM-AQ/EC模拟的1995~2004年的沙尘起沙量和干湿沉降量,分析了沙尘气溶胶源汇的全球时空变化特征.全球沙尘起沙量集中在各个主要沙漠地区,北非对全球沙尘气溶胶贡献最大为66.6%.沙尘气溶胶沉降的高值区分布在沙漠源区及其紧临的下风地区.最大净沙尘气溶胶接收主要分布在沙漠周围地区并形成净接收量大于10t/(km2×a)的位于0°N~60°N之间的北非、欧亚大陆、西太平洋、北印度洋、北美和大西洋的带状分布.在北非、阿拉伯半岛、中亚、东亚和澳大利亚5个主要沙漠地区中,起沙量和沉降量都存在明显的季节变化,除中亚其他4个区域干湿沉降量和起沙的季节变化基本一致;东亚地区沙尘气溶胶起沙量和总沉降量的季节变化最为明显,而北非沙漠起沙量和总沉降量的季节变化最小,其他3个区域的季节变化幅度基本相同.中亚起沙峰值和阿拉伯半岛起沙次峰值出现在夏季,其他区域的峰值均出现在春季.10年间全球陆地年平均起沙量为(1500±94)Mt,保持略微上升趋势.以北非沙漠起沙量年际变化率最低(6.3%), 而以东亚(28.3%)和澳大利亚(45.0%)起沙量年际变化最为明显;全球陆地的沙尘气溶胶沉降量以约9.9Mt/a的速率递减,全球海洋的沙尘气溶胶沉降递增.     

植被覆盖度与沙尘暴形成条件分析

以归一化差值植被指数（Normalized Difference Vegetation Index,NDVI）为指标分析了我国1981年到1998年期间植被覆盖变化情况,给出了植被急剧减少产生新沙源的实例。通过对1998年4月强沙尘暴的分析,指出影响沙尘暴产生和运移的因素除了地形、风速、风向、大气稳定度外,当地植被覆盖和土壤因素也是关键因素之一。并通过对植被覆盖度（NDVI）与浮尘指数（Aerosol Index）进行定量分析,发现二者之间存在明显的负相关关系,表明植被的存在可以从一定程度上抑制浮尘现象的产生。因此,在沙尘运移路径上,采取封山封荒,植树种草,增加植被覆盖度以固结当地土壤和泥沙的措施,可以在一定程度上抑制沙尘暴灾害的发生。     

热气溶胶灭火剂扑灭固体木垛火的实验研究

文章系统分析了热气溶胶灭火剂抑制A类火能力的影响因素,并用SQ灭火剂在全淹没条件下进行实验,研究了灭火剂用量、灭火室大小、木垛的预燃程度和木垛结构大小对灭火效果的影响规律,结果表明SQ热气溶胶灭火剂抑制A类火比B类火困难得多,此外灭火效果与木垛预燃程度、木垛的结构尺寸有关,与灭火实验所用的灭火室大小关系不大。并指出在评价热气溶胶灭火剂扑灭A类木垛火能力时,应详细给出灭火实验所采用的条件,特别是火灾模型的情况。     

气溶胶中多环芳烃的污染源识别方法

文章评述了气溶胶中多环芳烃污染源类型识别的几种方法,即:比值法、轮廓图法、特征化合物法和多元统计方法等.比值法简单可行,应用较多,但常因苯并(a)芘的不稳定性而带来误差,建议与轮廓图法、特征化合物法等配合使用,多元统计法要求样品数多,并且运算复杂,目前应用尚不多见,但其潜力很大。      

双波长气溶胶粒径传感方法及其火灾烟雾探测器

提出了双波长光散射气溶胶粒径传感方法,设计实现了采用该方法的双波长火灾烟雾探测器。使用短波长和长波长的双波长光源,通过计算其光功率比值,利用其与中值粒径的关系函数获得气溶胶粒径,并根据不同粒径下的气溶胶浓度分别给出大小不同粒径的火灾烟雾或干扰气溶胶提示。因而,不仅可以有效区分大小不同粒径的火灾烟雾气溶胶,以正确探测火灾,而且能够识别微米级的大粒径干扰粒子,降低火灾误报率,可以应用于飞机等航空器空中密闭的特殊环境。     

New insights into the formation of ammonium nitrate from a physical and chemical level perspective

● Factor analysis of ammonium nitrate formation based on thermodynamic theory. ● Aerosol liquid water content has important role on the ammonium nitrate formation. ● Contribution of coal combustion and vehicle exhaust is significant in haze periods. High levels of fine particulate matter (PM_2.5) is linked to poor air quality and premature deaths, so haze pollution deserves the attention of the world. As abundant inorganic components in PM_2.5, ammonium nitrate (NH₄NO₃) formation includes two processes, the diffusion process (molecule of ammonia and nitric acid move from gas phase to liquid phase) and the ionization process (subsequent dissociation to form ions). In this study, we discuss the impact of meteorological factors, emission sources, and gaseous precursors on NH₄NO₃ formation based on thermodynamic theory, and identify the dominant factors during clean periods and haze periods. Results show that aerosol liquid water content has a more significant effect on ammonium nitrate formation regardless of the severity of pollution. The dust source is dominant emission source in clean periods; while a combination of coal combustion and vehicle exhaust sources is more important in haze periods. And the control of ammonia emission is more effective in reducing the formation of ammonium nitrate. The findings of this work inform the design of effective strategies to control particulate matter pollution.     

对大气气溶胶降尘与降雨相关性分析的探讨

为了了解大气气溶胶降尘与降水的关系,本文通过对例行监测数据进行统计整理,并进行相关性检验分析,得出大气气溶胶降尘与降水pH值具有一定的相关性,且呈正相关,降水pH值与降雨量、降尘与降雨量之间则无相关性。     

Au nanoring arrays as surface enhanced Raman spectroscopy substrate for chemical component study of individual atmospheric aerosol particle

Monolayer-ordered gold nanoring arrays were prepared by ion-sputtering method and used as surface enhanced Raman spectroscopy (SERS) substrates to test the individual atmospheric aerosols particle. Compared to other methods used for testing atmospheric aerosols particles, the collection and subsequent detection in our work is performed directly on the gold nanoring SERS substrate without any treatment of the analyte. The SERS performance can be tuned by changing the depth of the gold nanoring cavity as originating from coupling of dipolar modes at the inner and outer surfaces of the nanorings. The electric field exhibits uniform enhancement and polarization in the ordered Au nanoring substrate, which can improve the accuracy for detecting atmospheric aerosol particles. Combined with Raman mapping, the information about chemical composition of individual atmospheric aerosols particle and distribution of specific components can be presented visually. The results show the potential of SERS in enabling improved analysis of aerosol particle chemical composition, mixing state, and other related physicochemical properties.