Abstract. An intensive aerosol and gases campaign was performed at Shanghai in the Yangtze River Delta region over Eastern China from late March to early June 2009. This study provided a complementary picture of typical haze types and the formation mechanisms in megacities over China by using a synergy of ground-based monitoring, satellite and lidar observations. During the whole study period, several extreme low visibility periods were observed with distinct characteristics, and three typical haze types were identified, i.e. secondary inorganic pollution, dust, and biomass burning. Sulfate, nitrate and ammonium accounted for a major part of PM2.5 mass during the secondary inorganic pollution, and the good correlation between SO2/NOx/CO and PM2.5 indicated that coal burning and vehicle emission were the major sources. Large-scale regions with high AOD (aerosol optical depths) and low Ångström exponent were detected by remote-sensing observation during the dust pollution episode, and this episode corresponded to coarse particles rich in mineral components such as Al and Ca contributing 76.8% to TSP. The relatively low Ca/Al ratio of 0.75 along with the air mass backward trajectory analysis suggested the dust source was from Gobi Desert. Typical tracers for biomass burning from satellite observation (column CO and HCHO) and from ground measurement (CO, particulate K+, OC, and EC) were greatly enhanced during the biomass burning pollution episode. The exclusive linear correlation between CO and PM2.5 corroborated that organic aerosol dominated aerosol chemistry during biomass burning, and the high concentration and enrichment degree of arsenic (As) could be also partly derived from biomass burning. Aerosol optical profile observed by lidar demonstrated that aerosol was mainly constrained below the boundary layer and comprised of spheric aerosol (depolarization ratio <5%) during the secondary inorganic and biomass burning episodes, while thick dust layer distributed at altitudes from near surface to 1.4 km (average depolarization ratio = 0.122 &amp;pm; 0.023) with dust accounting for 44–55% of the total aerosol extinction coefficient during the dust episode. This study portrayed a good picture of the typical haze types and proposed that identification of the complicated emission sources is important for the air quality improvement in megacities in China.

Abstract. Surface ozone has been severe during summers in the eastern parts of China, damaging human health and flora and fauna. During 2015–2018, ground-level ozone pollution increased and intensified from south to north. In North China and the Huanghuai region, the O3 concentrations were highest. Two dominant patterns of summer ozone pollution were determined, i.e., a south–north covariant pattern and a south–north differential pattern. The anomalous atmospheric circulations composited for the first pattern manifested as a zonally enhanced East Asian deep trough and as a western Pacific subtropical high, whose western ridge point shifted northward. The local hot, dry air and intense solar radiation enhanced the photochemical reactions to elevate the O3 pollution levels in North China and the Huanghuai region; however, the removal of pollutants was decreased. For the second pattern, the broad positive geopotential height anomalies at high latitudes significantly weakened cold air advection from the north, and those extending to North China resulted in locally high temperatures near the surface. In a different manner, the western Pacific subtropical high transported sufficient water vapor to the Yangtze River Delta and resulted in a locally adverse environment for the formation of surface ozone. In addition, the most dominant pattern in 2017 and 2018 was different from that in previous years, which is investigated as a new feature.

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&lt;p&gt;&lt;strong&gt;Abstract.&lt;/strong&gt; Surface ozone, a man-made air pollutant, has been severe during summers in the eastern parts of China, damaging human&amp;#8217;s health and flora and fauna. During 2015&amp;#8211;2018, ground-level ozone pollution increased year by year and intensified from south to north. In North China and Huanghuai region, the O&lt;sub&gt;3&lt;/sub&gt; concentrations were highest. Two dominant patterns of summer ozone pollution were determined, i.e., a south-north covariant pattern and a south-north differential pattern. The anomalous atmospheric circulations composited for the first pattern manifested as a zonally enhanced East Asia deep trough and as a west Pacific subtropical high whose western ridge point shifted northward. The local hot, dry air and intense solar radiation enhanced the photochemical reactions to elevate the O&lt;sub&gt;3&lt;/sub&gt; pollution levels in North China and Huanghuai region. For the second pattern, the broad positive geopotential height anomalies at high latitudes significantly weakened cold air activity, and those extending to North China resulted in locally high temperature near the surface. In a different manner, the west Pacific subtropical high transported sufficient water vapor to the Yangtze River Delta and resulted in locally adverse environment for the formation of surface ozone. Furthermore, the implications for the interannual differences in summer O&lt;sub&gt;3&lt;/sub&gt; pollution have also proven to be meaningful.&lt;/p&gt;