An Air Stagnation Index to Qualify Extreme Haze Events in Northern China

Abstract

Stagnation weather affects atmospheric diffusion ability, and hence causes the occurrence of haze events, which have been happening frequently in northern China (NC). This work puts forward an air stagnation index (ASITS) to characterize the stagnation weather in NC, in which the processes of ventilation, vertical diffusion, and wet deposition potency are concerned. ASITS can be applied to analyze air stagnation conditions with daily to monthly time scale. It is shown that the ASITS and particulate matter smaller than 2.5 μm in diameter (PM2.5) concentrations own similar lognormal probability distribution functions on both daily and monthly time scales. And the correlation analyses between the ASITS and PM2.5 concentrations indicate that the ASITS can reflect the monthly and daily variations in PM2.5 concentrations in NC. In addition, ASITS could be used as a leading predictor of haze events since correlation coefficients of ASITS leading PM2.5 concentrations by 1 day were significant and were larger than simultaneous correlation coefficients in almost all areas in NC. The robust relationship between ASITS and PM2.5 concentrations exists possibly because the index can reflect the activities of synoptic systems. ASITS could be a useful statistical indicator for variations in PM2.5 concentrations and haze events, and a good tool in analyzing the relationship between climate change and long-term variations in haze in NC.

Novel Method for Ozone Isopleth Construction and Diagnosis for the Ozone Control Strategy of Chinese Cities

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Application of Empirical Orthogonal Function Interpolation to Reconstruct Hourly Fine Particulate Matter Concentration Data in Tianjin, China

“…Generally, it is believed that high PM2.5 concentration has become a prominent challenge for air pollution control in China, which is mainly caused by the industrial combustion of coal and gasoline, traffic emissions, and long-distance transport [4,5]. e North China Plain, especially the Beijing-Tianjin-Hebei region (Figure 1(a)), is one of the regions most severely affected by the hazy weather [4,6]. To monitor air pollution, many urban environmental stations have been built in this region, and many researchers have analyzed the causes and behavior of high PM2.5 concentration recently [3,7].…”

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“…6a, b). This pattern bears some resemblance to the anomalous circulation associated with a positive phase of the Arctic Oscillation, which may be due to melting Arctic sea ice (Shindell et al, 1999;Fyfe et al, 1999;Wang et al, 2020). The southerly wind anomalies over eastern China, on the western flank of the anomalous anticyclone, act to weaken the East Asian winter monsoon and reduce its low-level winds, making conditions favorable for air-pollutant transport from south to north and air-pollutant accumulation more likely.…”