Vertical and horizontal distribution of submicron aerosol chemical composition and physical characteristics across northern India during pre-monsoon and monsoon seasons
Vertical and horizontal distribution of submicron aerosol chemical composition and physical characteristics across northern India during pre-monsoon and monsoon seasons
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DOI：
10.5194/acp-19-5615-2019
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发表时间：
2019-04-30
影响因子：
6.3
通讯作者：
Coe, Hugh
中科院分区：
文献类型：
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作者：
Brooks, James;Allan, James D.;Coe, Hugh
第一次利用空中原位测量，对印度北方各地亚微米气溶胶的物理和化学性质的垂直分布进行了表征。这项研究主要集中在印度-恒河平原，在印度北部的低洼地区，通常经历高气溶胶质量浓度的季风季节之前。所提供的数据来自英国机载大气测量设施BAe-146研究飞机，该飞机在2016年前季风期间在该地区进行了飞行（6月11日和12日）和季风（6月30日至7月11日）季节。在印度-恒河平原边界层内，有机物占亚微米气溶胶质量的主导地位（43%），其次是硫酸盐（29%），铵（14%）、硝酸盐（7%）和黑碳（7%）。然而，在印度-恒河平原之外，硫酸盐是主要的种类，占边界层中亚微米气溶胶总质量的44%，其次是有机物（30%），铵（14%），硝酸盐（6%）和黑碳（6%）。在整个活动中，氯的质量浓度可以忽略不计。印度-恒河平原内部的黑碳质量浓度（2 μ g m（-3））高于外部（1 μ g m（-3））。硝态氮受热力学过程控制，在较低温度和较高相对湿度的条件下，硝态氮的质量浓度增加。增加的质量和数量的浓度内观察到的印度-恒河平原和气溶胶是更多的吸收在这一地区，而外的印度-恒河平原的气溶胶的尺寸更大，更分散的性质，这表明更大的灰尘存在，特别是在印度西北部。随着季风季节的推进，气溶胶成分基本保持相似，但总气溶胶质量浓度随着降雨的到来下降了约50%;季风前的平均总质量浓度为30 μ g m（-3），而季风平均总质量浓度为10-20 μ g m（-3）。然而，在印度恒河平原，这种质量浓度下降不太值得注意（类似于20%-30%），这可能是由于该地区排放源的强度。随着季风的到来，粗模态气溶胶减少，细模态分数增加。在气溶胶垂直廓线中，在前季风期间，在印度-恒河平原内，有机气溶胶和吸收气溶胶物种在低层大气（< 1.5 km）中占主导地位，硫酸盐，灰尘和其他散射气溶胶物种在1.5 km以上的气溶胶层中增强，最大气溶胶高度约为6 km。在海拔1.5公里以上的地方，沙尘浓度升高，这清楚地表明沙尘是从印度西北部的大印度沙漠（也称为塔尔沙漠）输送过来的。随着季风进入该地区，气溶胶层的升高减少，气溶胶最大高度降低到2公里左右。灰尘和硫酸盐占主导地位的气溶胶层高空被删除后，季风的到来，突出了整个配置文件中的细模分数的增加。
The vertical distribution in the physical and chemical properties of submicron aerosol has been characterised across northern India for the first time using airborne in situ measurements. This study focusses primarily on the Indo-Gangetic Plain, a low-lying area in the north of India which commonly experiences high aerosol mass concentrations prior to the monsoon season. Data presented are from the UK Facility for Airborne Atmospheric Measurements BAe-146 research aircraft that performed flights in the region during the 2016 pre-monsoon (11 and 12 June) and monsoon (30 June to 11 July) seasons.Inside the Indo-Gangetic Plain boundary layer, organic matter dominated the submicron aerosol mass (43 %) followed by sulfate (29 %), ammonium (14 %), nitrate (7 %) and black carbon (7 %). However, outside the Indo-Gangetic Plain, sulfate was the dominant species, contributing 44% to the total submicron aerosol mass in the boundary layer, followed by organic matter (30 %), ammonium (14 %), nitrate (6 %) and black carbon (6 %). Chlorine mass concentrations were negligible throughout the campaign. Black carbon mass concentrations were higher inside the Indo-Gangetic Plain (2 mu g m(-3)) compared to outside (1 mu g m(-3)). Nitrate appeared to be controlled by thermodynamic processes, with increased mass concentration in conditions of lower temperature and higher relative humidity. Increased mass and number concentrations were observed inside the Indo-Gangetic Plain and the aerosol was more absorbing in this region, whereas outside the Indo-Gangetic Plain the aerosol was larger in size and more scattered in nature, suggesting greater dust presence, especially in north-western India. The aerosol composition remained largely similar as the monsoon season progressed, but the total aerosol mass concentrations decreased by similar to 50% as the rainfall arrived; the pre-monsoon average total mass concentration was 30 mu g m(-3) compared to a monsoon average total mass concentration of 10-20 mu g m(-3). However, this mass concentration decrease was less noteworthy (similar to 20 %-30 %) over the Indo-Gangetic Plain, likely due to the strength of emission sources in this region. Decreases occurred in coarse mode aerosol, with the fine mode fraction increasing with monsoon arrival. In the aerosol vertical profile, inside the Indo-Gangetic Plain during the pre-monsoon, organic aerosol and absorbing aerosol species dominated in the lower atmosphere (< 1.5 km), with sulfate, dust and other scattering aerosol species enhanced in an elevated aerosol layer above 1.5 km with maximum aerosol height similar to 6 km. The elevated concentration of dust at altitudes > 1.5 km is a clear indication of dust transport from the Great Indian Desert, also called the Thar Desert, in north-western India. As the monsoon progressed into this region, the elevated aerosol layer diminished, the aerosol maximum height reduced to similar to 2 km. The dust and sulfate-dominated aerosol layer aloft was removed upon monsoon arrival, highlighted by an increase in fine mode fraction throughout the profile.