Classification and Investigation of Asian Aerosol Properties

Abstract

Ongoing urbanization and industrialization in East Asia have generated a wide variety of aerosols in the atmosphere and have consequently added more uncertainty when evaluating global climate change.  To classify different types of aerosols and investigate their physical and chemical properties, four AErosol RObotic NETwork (AERONET) sites have been selected to represent aerosol properties dominated by mixed complex particle types (Xianghe and Taihu), desert-urban (SACOL), and biomass (Mukdahan) over East Asia during the 2001-2010 period.  The volume size distribution, aerosol optical depth [t(l) and t_abs(l)], Ångström exponent (a and a_abs), and the single scattering co-albedo [w_oabs(l)] and a(w_oabs) parameters over the four selected sites have been analyzed.  These parameters are used to (a) investigate the aerosol properties and their seasonal variations over the four selected sites, (b) discern the different absorptive characteristics of BC, OC, and mineral dust particles using a_abs440-870 and a(w_oabs440-870), and (c) develop an aerosol clustering method involving a_440-870 and w_oabs440.  A strong mineral dust influence is seen at the Xianghe, Taihu, and SACOL sites during the spring months (MAM) as given by coarse mode size distribution dominance, declining a_440-870, and elevated a_abs440-870 and a(w_oabs440-870) values.  A weakly absorbing pollution (OC and biomass) aerosol dominance is seen in the summer (JJA) and autumn (SON) months as given by a strong fine mode influence, increasing a_440-870, and declining a_abs440-870 and a(w_oabs440-870) values.  A winter season (DJF) shift toward strongly absorbing BC particles is observed at Xianghe and Taihu (elevated a_440-870, increase in a_abs440-870 and a(w_oabs440-870)).  At Mukdahan, a fine mode biomass particle influence is observed year round as given by the volume size distribution, elevated a_440-870 (higher than the other sites), low a_abs440-870 and negative a(w_oabs440-870) values indicating weakly absorbing OC particles.  The a(w_oabs) parameter is also shown to have less overlap in values than a_abs in discerning influences from OC, BC, biomass and mineral dust particles.  The clustering method using a_440-870 and ω_oabs440 illustrates four groups of aerosols:  Cluster I – fine mode, weakly absorbing pollution particles, Cluster II – fine mode, strongly absorbing pollution particles, Cluster III – coarse mode, strongly absorbing mineral dust particles, and Cluster IV – biomass particles with similar characteristics as Cluster II but less absorbing.  This method has shown that aerosol mixtures are both seasonal and regional combinations of particles that were either locally generated or transported from other source regions and should be implemented over other AERONET sites in the future.