Regional air pollution is significantly associated with dominant weathersystems. In this study, the relationship between the particle pollution overthe Yangtze River Delta (YRD) region and weather patterns is investigated.First, the pollution characteristics of particles in the YRD are studiedusing in situ monitoring data (PM and PM) in 16 cities andTerra/MODIS AOD (aerosol optical depth) products collected from December 2013to November 2014. The results show that the regional mean value of AOD ishigh in the YRD, with an annual mean value of 0.71±0.57. The annual meanparticle concentrations in the cities of Jiangsu Province all exceed thenational air quality standard. The pollution level is higher in inland areas,and the highest concentrations of PM and PM are 79 and130 µg m, respectively, in Nanjing. ThePM : PM ratios are typically high, thus indicating thatPM is the overwhelmingly dominant particle pollutant in the YRD. Thewintertime peak of particle concentrations is tightly linked to the increasedemissions during the heating season as well as adverse meteorologicalconditions. Second, based on NCEP (National Center for Environmental Prediction) reanalysis data, synoptic weatherclassification is conducted and five typical synoptic patterns areobjectively identified. Finally, the synthetic analysis of meteorologicalfields and backward trajectories are applied to further clarify how thesepatterns impact particle concentrations. It is demonstrated that airpollution is more or less influenced by high-pressure systems. The relativeposition of the YRD to the anti-cyclonic circulation exerts significanteffects on the air quality of the YRD. The YRD is largely influenced bypolluted air masses from the northern and the southern inland areas when itis located at the rear of the East Asian major trough. The significantdownward motion of air masses results in stable weather conditions, therebyhindering the diffusion of air pollutants. Thus, this pattern is quitefavorable for the accumulation of pollutants in the YRD, resulting in higherregional mean PM (116.5 ± 66.9 µg m),PM (75.9 ± 49.9 µg m), and AOD (0.74) values.Moreover, this pattern is also responsible for the occurrence of mostlarge-scale regional PM (70.4 %) and PM (78.3 %)pollution episodes. High wind speed and clean marine air masses may also playimportant roles in the mitigation of pollution in the YRD. Especially whenthe clean marine air masses account for a large proportion of alltrajectories (i.e., when the YRD is affected by the cyclonic system oroceanic circulation), the air in the YRD has a lesser chance of beingpolluted. The observed correlation between weather patterns and particlepollution can provide valuable insight into making decisions about pollutioncontrol and mitigation strategies.
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