Climatological study of the Boundary-layer air Stagnation Index for China and its relationship with air pollution

Abstract

Abstract. The Air Stagnation Index (ASI) is a vital meteorological measure of the atmosphere's ability to dilute air pollutants. The original metric adopted by the US National Climatic Data Center (NCDC) is found to be not very suitable for China, because the decoupling between the upper and lower atmospheric layers results in a weak link between the near-surface air pollution and upper-air wind speed. Therefore, a new threshold for the ASI-Boundary-layer air Stagnation Index (BSI) is proposed, consisting of daily maximal ventilation in the atmospheric boundary layer, precipitation, and real latent instability. In the present study, the climatological features of the BSI are investigated. It shows that the spatial distribution of the BSI is similar to the ASI; that is, annual mean stagnations occur most often in the northwestern and southwestern basins, i.e., the Xinjiang and Sichuan basins (more than 180 days), and least over plateaus, i.e., the Qinghai-Tibet and Yunnan plateaus (less than 40 days). However, the seasonal cycle of the BSI is changed. Stagnation days under the new metric are observed to be maximal in winter and minimal in summer, which is positively correlated with the air pollution index (API) during 2000-2012. The correlations between the BSI and the concentration of fine particulate matter (PM 2.5 ) during January 2013 and November to December in 2015-2017 of Beijing are also investigated. It shows that the BSI matches the day-by-day variation of PM 2.5 concentration very well and is able to catch the haze episodes.

The significant impact of aerosol vertical structure on lower atmosphere stability and its critical role in aerosol–planetary boundary layer (PBL) interactions

“…Conventionally, increasing the aerosol absorption tends to stabilize the atmosphere, leading to a reduced PBL height (PBLH). A more stable atmosphere and lower PBLH will, in turn, increase the surface aerosol loading, which is the well-established positive feedback loop in the aerosol-PBL interaction (e.g., Wang et al, 2015;Ding et al, 2016;Petäjä et al, 2016;Dong et al, 2017;Zou et al, 2017;Q. Huang et al, 2018;Wang et al, 2019).…”

Supplementary material to "Heavy air pollution with the unique “non-stagnant” atmospheric boundary layer in the Yangtze River Middle Basin aggravated by regional transport of PM<sub>2.5</sub> over China"

“…Climatologically, a strong northerly wind, low air temperature and high air pressure are typical features of an incursion of cold air during East Asian winter monsoon season in central-eastern China, which could disperse air pollutants and improve air quality in the NCP region (Miao et al, 2018;Xu et al, 2016b). Compared to the meteorological conditions for stagnation with weak winds observed for heavy air pollution events in the major air pollution regions of central-eastern China (Huang et al, 2018;Ding et al, 2017), meteorological conditions with strong near-surface wind were anomalously accompanied with the intensification of PM2.5…”

“…The accumulationoutbreak, maintenance and dissipation of haze pollution events are generally determined by meteorological changes (Kan et al, 2012), among which the boundary layer structures play the most important role (Wu et al, 2017). Meteorological conditions of stagnation characterized by near-surface low winds, high humidity and stable boundary layer could govern the periodic variations of haze pollution, which present as typical wintertime air pollution in central-eastern China (Xu et al, 2016b;Huang et al, 2018). Four major regions exhibiting haze pollution with high PM2.5 concentrations and overall poor air quality are centered over North China Plain (NCP), Yangtze River Delta (YRD) in East China, Pearl River Delta (PRD) in South China and Sichuan Basin (SCB) in Southwest China (Cheng et al, 2008;Zhang et al, 2012;Deng et al, 2011;Wang et al, 2016;Tie et al, 2017;Qiao et al, 2019).…”

Estimation of greenhouse gas emission factors based on observed covariance of CO2, CH4, N2O and CO mole fractions

“…The scientific literature is rich in indexes for the identification of stagnant weather conditions favorable for the accumulation of air pollutants (see e.g., [31,[51][52][53][54][55][56][57]and references therein). These indexes comprised different meteorological variables to describe the reduced dispersion processes.…”