Long-range transport of aerosols from East and Southeast Asia to northern Philippines and its direct radiative forcing effect

Two elevated fine particulate mass concentration events were observed in a span of a week in northern Philippines on March of 2017. Results from chemical characterization, lidar observation, and model simulations of particulate matter show the high aerosol concentration events to be caused by long range transport (LRT) of anthropogenic pollutants from northern East Asia at the surface and biomass burning emission from Indochina aloft. In this study, we investigated the transport path of these LRT aerosols and estimated their direct radiative forcing. A strong Siberian high and a confluent flow induced by a continental high over the main Asian continent and a cyclonic circulation over the south of Japan produced a strong northerly wind that carried pollutants from northern East Asia to northern Philippines. At the same time, strong westerlies 2-4 km aloft carried biomass burning emissions from Indochina, which also had an impact on ground concentration. Mass extinction efficiency of LRT aerosols was estimated to be in the range of 2.06-6.44 m(2) g(-1) with a mean value of 4.32 +/- 1.32 m(2) g(-1). In addition, we calculated the direct radiative forcing effect under clear sky condition and found that the transported aerosols had a mean net negative forcing (cooling) effect of -50.80 +/- 12.38 Wm(-2) and -11.98 +/- 3.96 Wm(-2) on surface and at the top of the atmosphere, respectively. Such pollutant transport during wintertime cold surges had been shown to reduce local surface pollutants in northern China. Consequently, its impacts shift to downwind regions as far as the Philippines. As winter cold surge frequency increases due to the warming arctic, more LRT events may be expected as a result of climate change.