Abstract:
Abstract : The composite characteristics of PM
2.5-O
3 in Shandong Province were relatively prominent and also showed obvious spatial differences. To study characteristics of co-pollution of surface O
3 and PM
2.5 in Shandong province, spatial distributions of the PM
2.5 and O
3 concentrations were analyzed and the relationship between O
3 and PM
2.5, meteorological parameters and their precursors were explored based on the monitoring data of national and provincial ambient air quality monitoring sites and meteorological sites from 2016 to 2020. The results indicated that: (1) During 2016-2020, the air quality in Shandong Province improved gradually with excellent and good days increasing by 7.1% and heavily polluted days decreasing by 3.5%. Except for the 90th percentile of the maximum daily 8-hour average of the O
3 concentrations (O
3 MDA8 90th), which increased by 9.6%, the concentrations of SO
2, PM
10, PM
2.5, CO and NO
2 decreased by 61.3%, 29.8%, 28.6%, 26.3% and 11.4%, respectively. The annual average values of PM
2.5 in all cities of Shandong Province declined with decreasing ratios ranging from 18.4% to 34.9%. The O
3 MDA8 90th increased in all the cities except for Dezhou City. The largest increasing ratio of O
3 MDA8 90th was 30.8% in Binzhou City. The highest average PM
2.5 concentrations was observed in January while the highest average O
3 concentration was observed in June. The PM
2.5 concentrations in January decreased and then increased from 2016 to 2020, while the O
3 concentrations in June increased from 2016 to 2020. (2) The PM
2.5 and O
3 concentrations in inland cities were higher than those in coastal cities with higher PM
2.5 concentration observed in western inland areas and higher O
3 concentrations in central and northern inland areas. Synergistic pollution characteristics of PM
2.5 and O
3 were obvious in the central and western Shandong Province. There were 224 days characterized by the synergistic pollution of PM
2.5 and O
3 during the whole study period, which mainly occurred from February to November. The days with the synergistic pollution of PM
2.5 and O
3 decreased year by year. (3) The correlationship between concentrations of PM
2.5 or O
3 and meteorological factors, as well as threshold of meteorological factors during PM
2.5, O
3 or PM
2.5-O
3 composite pollutant days, were also carried out. The results showed that the daily average PM
2.5 and O
3_8 h concentrations had negative correlations with their precursors and meteorological parameters. Moreover, spatial differences existed in the correlation between PM
2.5 and O
3, their precursors and meteorological parameters. The statistical results show that PM
2.5-O
3 complex pollution favorably occurred when the atmospheric temperature, relative humidity, wind speed and atmospheric pressure ranged from 14.9-24.1 °C, from 55.5%-75.1%, 0.6-2.9 m/s and 992.8-1018.8 hPa, respectively. In most cities of Shandong Province, the average values of atmospheric temperature, relative humidity and atmospheric pressure during the synergistic pollution of PM
2.5 and O
3 were between those during the PM
2.5 pollution and those during the O
3 pollution. But the average wind speed during the synergistic pollution of PM
2.5 and O
3 was lower than those during the PM
2.5 pollution and during the O
3 pollution. In summary, the study showed that on a whole the PM
2.5 concentration declined but the O
3 concentration enhanced, and synergistic changes of PM
2.5 and O
3 became more obvious during the ‘13th Five-Year Plan’ period. Meteorological factors played a role in the formation and accumulation of PM
2.5 and O
3.
Keywords : PM
2.5 and O
3; pollution characteristics; temporal and spatial distribution; meteorological factors; Shandong Province