The Yangtze River Delta (YRD) is one of the most densely populated regions in China with severe air quality issues that have not been fully understood. Thus, in this study, based on 1-year (2013) continuous measurement at a National Reference Climatological Station (NRCS, 30.22°?N, 120.17°?E; 41.7?m?a.s.l.) in the center of Hangzhou in the YRD, we investigated the seasonal characteristics, interspecies relationships, and the local emissions and the regional potential source contributions of trace gases (including Osub3/sub, NOsubix/i/sub, NOsubiy/i/sub, SOsub2/sub, and CO) and particulate matter (PMsub2.5/sub and PMsub10/sub). Results revealed that severe two-tier air pollution (photochemical and haze pollution) occurred in this region, with frequent exceedances in Osub3/sub (38?days) and PMsub2.5/sub (62?days). Osub3/sub and PMsub2.5/sub both exhibited distinct seasonal variations with reversed patterns: Osub3/sub reaching a maximum in warm seasons (May and July) but PMsub2.5/sub reaching a maximum in cold seasons (November to January). The overall results from interspecies correlation indicated a strong local photochemistry favoring the Osub3/sub production under a volatile organic compound (VOC)-limited regime, whereas it moved towards an optimum Osub3/sub production zone during warm seasons, accompanied by the formation of secondary fine particulates under high Osub3/sub. The emission maps of PMsub2.5/sub, CO, NOsubix/i/sub, and SOsub2/sub demonstrated that local emissions were significant for these species on a seasonal scale. The contributions from the regional transport among inland cities (Zhejiang, Jiangsu, Anhui, and Jiangxi Province) on a seasonal scale were further confirmed to be crucial to air pollution at the NRCS site by using backward trajectory simulations. Air masses transported from the offshore areas of the Yellow Sea, East Sea, and South Sea were also found to be highly relevant to the elevated Osub3/sub at the NRCS site through the analysis of potential source contribution function (PSCF). Case studies of photochemical pollution (Osub3/sub) and haze (PMsub2.5/sub) episodes both suggested the combined importance of local atmospheric photochemistry and synoptic conditions during the accumulation (related with anticyclones) and dilution process (related with cyclones). Apart from supplementing a general picture of the air pollution state in the city of Hangzhou in the YRD region, this study specifically elucidates the role of local emission and regional transport, and it interprets the physical and photochemical processes during haze and photochemical pollution episodes. Moreover, this work suggests that cross-regional control measures are crucial to improve air quality in the YRD region, and it further emphasizes the importance of local thermally induced circulation for air quality.
展开▼
