Abstract
ABSTRACT By utilizing observation and reanalysis data and statistical methods to comprehensively assess the main characteristics of particulate matter (PM) on the low-latitude plateau (LoLaP) of southwestern China, this study analyzed the influence of the Kunming quasi-stationary front (KMQSF) on the PM concentration during winter in this region. We found that the location and intensity of the KMQSF significantly affected the distribution pattern of the PM and induced high concentrations in some areas during a typical pollution event in 2016. Furthermore, we investigated all of the KMQSF synoptic weather that occurred from 2014 till 2019 and categorized it into nine types, which produced different pollution patterns. When the KMQSF moved westward from the center of the LoLaP, the easterly wind transported PM to the western part of the region, which led to an increase in the mean daily PM10 and PM2.5 concentrations in Kunming, a capital city in that area; simultaneously, however, the PM10 and PM2.5 levels remained high in Guiyang, a capital city in the eastern part of the LoLaP. When the KMQSF gradually retreated from the western to the eastern part of the LoLaP, the PM in Kunming dropped as the westerly wind increased in strength, whereas the PM in Guiyang continued to rise as the planetary boundary layer (PBL) height (PBLH) and boundary layer dissipation (BLD) rate decreased. When the KMQSF disappeared, temperature inversion, a shallow PBL and weak BLD across the entire region caused pollutants to accumulate, resulting in the highest mean daily PM10 and PM2.5 concentrations for both cities.
Highlights
Analyzing the PM10, PM2.5 and PM1 concentrations for November 2016–May 2017 in downtown Kunming (Donglu), we identified the causes of a pollution episode during 2016 and evaluated the relationship between the Kunming quasi-stationary front (KMQSF) and the fine particle concentrations on the low-latitude plateau (LoLaP) between November and February for the years 2014–2019
From December 4 till 9, the KMQSF weakened to the east of Kunming, and both Kunming and Guiyang exhibited low wind speed, low PBL height (PBLH), weak boundary layer dissipation (BLD), high relative humidity (RH) and ground temperature inversions
Identifying nine KMQSF synoptic weather patterns, we discovered that the pollution observed during Patterns 8 and 9 was mainly contributed by local emission on the western LoLaP and there was pollution transport from surrounding areas on the eastern LoLaP
Summary
Air pollution has been a global issue over the past several decades (Ding et al, 2013; Duncan et al, 2016; Bian et al, 2017; Davis, 2017) due to its harmful influences on human health (Lelieveld et al, 2015; Raaschou-Nielsen et al, 2017) and ecosystems as well as its severe impacts on climate (Knippertz et al, 2015; Acosta Navarro et al, 2016; Li et al, 2016; Lau et al, 2017) and synoptic systems (Gong et al, 2014; Fan et al, 2015). Various meteorological factors play critical roles: moist air, a shallow PBL, temperature inversions and weak/calm wind conditions. 61.5% of the KMQSF was located east of 103°E during 1961–2010 This synoptic system is usually caused by the confrontation between the southwestern warm air and the cold air from the polar region that is stopped by the Tibetan Plateau and the LoLaP (Duan et al, 2017), and there are significant differences in the weather and climatic characteristics of the pre-frontal and post-frontal sectors (Fig. 1(a)) (Sheng et al, 2015).
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