Classification of summertime synoptic patterns in Beijing and their associations with boundary layer structure affecting aerosol pollution

Abstract

Abstract. Meteorological conditions within the planetary boundary layer (PBL) are closely governed by large-scale synoptic patterns and play important roles in air quality by directly and indirectly affecting the emission, transport, formation, and deposition of air pollutants. Partly due to the lack of long-term fine-resolution observations of the PBL, the relationships between synoptic patterns, PBL structure, and aerosol pollution in Beijing have not been well understood. This study applied the obliquely rotated principal component analysis in T-mode to classify the summertime synoptic conditions over Beijing using the National Centers for Environmental Prediction reanalysis from 2011 to 2014, and investigated their relationships with PBL structure and aerosol pollution by combining numerical simulations, measurements of surface meteorological variables, fine-resolution soundings, the concentration of particles with diameters less than or equal to 2.5 µm, total cloud cover (CLD), and reanalysis data. Among the seven identified synoptic patterns, three types accounted for 67 % of the total number of cases studied and were associated with heavy aerosol pollution events. These particular synoptic patterns were characterized by high-pressure systems located to the east or southeast of Beijing at the 925 hPa level, which blocked the air flow seaward, and southerly PBL winds that brought in polluted air from the southern industrial zone. The horizontal transport of pollutants induced by the synoptic forcings may be the most important factor affecting the air quality of Beijing in summer. In the vertical dimension, these three synoptic patterns featured a relatively low boundary layer height (BLH) in the afternoon, accompanied by high CLD and southerly cold advection from the seas within the PBL. The high CLD reduced the solar radiation reaching the surface, and suppressed the thermal turbulence, leading to lower BLH. Besides, the numerical sensitive experiments show that cold advection induced by the large-scale synoptic forcing may have cooled the PBL, leading to an increase in near-surface stability and a decrease in the BLH in the afternoon. Moreover, when warm advection appeared simultaneously above the top level of the PBL, the thermal inversion layer capping the PBL may have been strengthened, resulting in the further suppression of PBL and thus the deterioration of aerosol pollution levels. This study has important implications for understanding the crucial roles that meteorological factors (at both synoptic and local scales) play in modulating and forecasting aerosol pollution in Beijing and its surrounding area.

Two decades of satellite observations of AOD over mainland China using ATSR-2, AATSR and MODIS/Terra: data set evaluation and large-scale patterns

“…This seasonal behavior is in contrast to that of near-surface aerosol concentrations, indicated, for instance, by PM 2.5 , i.e., the mass concentration of dry particles with in situ diameters smaller than 2.5 µm, which peak in the winter and reach a minimum in the summer (e.g., Wang et al, 2015). These differences can be explained by seasonal variations in synoptic patterns (Xia et al, 2007;Miao et al, 2017) and associated boundary layer height and relative humidity, transport of aerosols, emission of primary aerosols and aerosol precursors contributing to chemical processes leading to secondary formation of new aerosol particles and thus higher concentrations (e.g., Tang et al, 2016). In particular, the seasonal emissions of dust aerosol (spring) and biomass burning aerosol (season varies with region) have a strong influence.…”

“…Many studies have been published on aerosols in relation to air quality in the eastern part of China, including satellite remote sensing, ground-based measurements, modeling and combinations thereof, which often focus on local or regional aspects (e.g., Song et al, 2009;Ma et al, 2016;Zou et al, 2017;Xue et al, 2017;Miao et al, 2017;Guo et al, 2017). Satellites offer the opportunity to obtain information, using the same instruments and methods, over a large area during a longer period of time.…”

Role of ambient ammonia in particulate ammonium formation at a rural site in the North China Plain

“…Hourly meteorological data were calculated from the in situ measurements and used in this paper. Planetary boundary layer height (PBLH) values at 14:00 BST (all times in Beijing standard time throughout the paper) were derived from the ERA-Interim data using the bulk Richardson number method Miao et al, 2017). (1)…”

Self-organized classification of boundary layer meteorology and associated characteristics of air quality in Beijing

“…1). Under favorable weather conditions (e.g., stagnant weather), terrain-related circulations can be well developed over Beijing and its surroundings, leading to a complex ABL structure, which is thought to substantially affect Beijing's air quality Miao et al, 2017;Ye et al, 2016;Gao et al, 2016;Xu et al, 2016). With high emissions of air pollutants from anthropogenic sources, Beijing is suffering serious air pollution problems and the pollution can be even more severe when southwesterly and southeasterly winds prevail within the ABL (Chen et al, 2008;Ye et al, 2016;Zhang et al, 2014Zhang et al, , 2012.…”