The Joint Graduate School of Energy and Environment, King Mongkut's University of Technology Thonburi, Bangkok, Thailand.
Center of Excellence on Energy Technology and Environment, Ministry of Higher Education, Science, Research and Innovation, Bangkok, Thailand.
Environ Monit Assess. 2022 Mar 31;194(4):322. doi: 10.1007/s10661-022-09880-2.
Visibility and aerosol optical depth (AOD) characterization, and their relationship with PM and local and synoptic meteorology, were studied for January-March in 2014 and 2015 over Bangkok. Visibility degradation intensifies in the dry season as compared to the wet season due to increase in PM and unfavorable meteorological conditions. The average visibility is lower in January and February as compared to the other months. Relatively higher AOD in March despite lower PM is attributed to the synergetic effect of moderate relative humidity, secondary aerosols, elevated aerosol layer due to summertime convection, and biomass burning. Larger variability in visibility and PM in winter months is due to more synoptic weather fluctuations while AOD shows similar variability for all months attributed partly to fires. Higher PM and moderate-to-high relative humidity cause lower visibility in the morning while it improves in afternoon as PM and relative humidity decrease. AOD is higher in the afternoon as compared to that in the morning and evening as it is less sensitive to diurnal change in aerosols and meteorology at the surface level. Visibility and AOD relationships with PM are dependent on relative humidity. Weaker winds lead to lower visibility, higher PM, and higher AOD irrespective of wind direction. Stronger winds improve visibility and decrease PM for all directions while AOD is higher for all directions except eastern and northeastern. The back-trajectory results show that the transport of pollutant and moist air is coupled with the synoptic weather and influence visibility and AOD. Two low-visibility events were investigated. The first event is potentially caused by the combined effect of local emissions and their accumulation due to stagnant weather conditions, secondary aerosols, and forest fires in the nearby regions. The second event can be attributed to the local emission and fires in the nearby area with hygroscopic growth of aerosols due to moist air from the Gulf of Thailand. Based on these findings, some policy implications have also been given.
本研究于 2014 年和 2015 年 1 月至 3 月在曼谷对大气能见度和气溶胶光学厚度（AOD）特征及其与 PM 及局地和天气系统气象条件的关系进行了研究。与雨季相比，旱季由于 PM 增加和不利的气象条件，大气能见度下降趋势更为严重。与其他月份相比，1 月和 2 月的平均能见度较低。尽管 PM 较低，但 3 月的 AOD 相对较高，这归因于中等相对湿度、二次气溶胶、夏季对流引起的气溶胶层抬升以及生物质燃烧的协同作用。冬季月份的能见度和 PM 变化较大是由于天气系统变化较多，而 AOD 所有月份的变化相似，部分原因是火灾。更高的 PM 和中等至高相对湿度导致早晨能见度较低，而随着 PM 和相对湿度的降低，下午能见度会有所改善。AOD 下午的值高于早晨和晚上，因为其对地表气溶胶和气象的日变化不太敏感。能见度和 AOD 与 PM 的关系取决于相对湿度。无论风向如何，较弱的风都会导致能见度降低、PM 增加和 AOD 升高。所有风向的强风都会提高能见度并降低 PM，而除了东风和东北风外，所有风向的 AOD 都更高。轨迹分析结果表明，污染物和潮湿空气的输送与天气系统相互作用，影响能见度和 AOD。本研究调查了两次低能见度事件。第一次事件可能是由于局地排放及其在停滞天气条件下的积累、二次气溶胶以及附近地区森林火灾的综合作用造成的。第二次事件可能是由于局地排放和附近地区的火灾以及来自泰国湾的潮湿空气引起的气溶胶吸湿增长造成的。基于这些发现，还提出了一些政策建议。
