Effects of synoptic circulation patterns on air quality in Nanjing and its surrounding areas during 2013–2015

Özet

The Yangtze River Delta region is the most active of China's economic regions; however, industrialization andurbanization have seriously affected air quality in the region and air pollution is becoming increasingly serious.Based on the NCEP/NCAR FNL reanalysis data of sea level pressure (SLP) from 2013 to 2015, an objectivequantitative method of synoptic circulation classification, T-mode principal component analysis (PCA), was usedto analyze the influence of synoptic circulation pattern on air quality in East China. Circulation was divided intonine types: (1) Northwest High Pressure (NWH); (2) Front of Low Pressure (FL); (3) North High Pressure (NH);(4) Northeast High Pressure (NEH); (5) South Low pressure (SL); (6) Weak pressure (Unique); (7) Southwest LowPressure (SWL); (8) Northeast Low Pressure (NEL); and (9) Low Pressure (L). The air quality in the Nanjing areais discussed in this paper, as well as the relationship between synoptic circulation patterns and local meteorologicalconditions. The results show that there is a close relationship between synoptic circulation patterns andlocal meteorological conditions that greatly affects the air quality of the Nanjing area. By the quantitativeanalysis of the concentrations of five air pollutants (PM2.5, CO, NO2, SO2 and O3) under different synopticcirculation types, it was found that circulation type 1 (CT 1, NWH), circulation type 3 (CT 3, NH) and circulationtype 4 (CT 4, NEH) were associated with poor air quality; the mean PM2.5 concentrations during 2013, 2014 and2015 were 83.8 μgm-3, 77.6 μgm-3 and 78.4 μgm-3, respectively. The local meteorological conditions correspondingto the three circulation types were low temperature and low wind speed. In contrast, circulation type 2(CT 2, FL) and circulation type 8 (CT 8, NEL), which were associated with better air quality, had opposite localmeteorological conditions; the mean PM2.5 concentrations were 53.2 μgm-3 and 57.7 μgm-3, respectively. Thiscase study shows that the Nanjing region was mainly controlled by CT 1 and CT 3 during the major pollutionevent in January 2015. The regional transport paths associated with specific circulation types were identified bytrajectory analysis in the haze episodes. It was found that two rainfall events played a positive role in improvingair quality in the Nanjing area.