A 9‐year climatology of airstreams in East Asia and implications for the transport of pollutants and downstream impacts

Abstract

[1] Ambient measurements of PM 10 levels in Taiwan over East Asia have shown unusual decreases for the 1994-2002 period. To assess these downward trends of PM 10 , we develop methods for calculating climatologies of PM 10 and airstreams, and a new method for quantifying airstreams and their associated impacts on PM 10 and PM 10 -influencing factors. These methods were verified against anomalously low PM 10 levels during the 1998 ENSO, and anomalously high PM 10 levels during spring 2000. Calculations show the following: 20-23% increased occurrence of airstreams from the north direction in spring 2000 coincide with 14-16% increases in ambient PM 10 levels downstream over Taiwan; 60% increased occurrence of airstreams over western Pacific coincide with 10-15% drops in ambient PM 10 levels downstream during the 1998 ENSO. Comparison of airstreams between 1994-1997 and 1999-2002 show a 15-29% reduction over the eastern direction and a 7-17% increase over the western direction. The most significant findings associated with these changes are the reduction in close-to-surface inversions, the increase in rainfall, the increase in continental outflows, and the counteracting effects between these processes. The reduction in close-to-surface inversions dilutes ambient particles from the surface toward the free troposphere, thereby reducing ambient PM 10 levels; increases in rainfall provide efficient wet scavenging mechanisms for removing particles from the ambient air. These two processes counteract and dominate over the increase in airstreams over the northwestern direction, where continental pollutants are exported downstream, and results in the downward trends in PM 10 .

Atmospheric wet deposition of trace metals in the Suwon region in Korea during farming periods

“…In this study, heavy metal EF values in the rainwater were greater than those of naturally derived elements such as Fe, Mg, and Ca. Wang (2005), who proposed the use of EFs concluded the following. An EF value between 1 and 10 represents a load that originates only from soil or crustal elements in a target area.…”

“…Notably, although Cd is present at small concentrations in the rainwater, it has a significant positive correlation with Pb, Zn and Ni. EFs (Conko et al, 2004;García et al, 2006;Wang, 2005) are relative indices for contamination, and are calculated for each heavy metal measured in rainwater, compared to their concentrations in the Earth's crust (Figure 3). Generally, if there is no anthropogenic contamination, then the concentrations can be considered as 'background', derived from natural sources.…”

“…The EFs, which represent relative indices of contamination for each heavy metal, were calculated to compare the contamination characteristics of heavy metals and other chemicals in rainwater (Conko et al, 2004;García et al, 2006;Wang, 2005). The EF is useful in evaluating the absolute contamination condition of a certain metal, compared to its background concentration.…”

“…In studying heavy metal loads, previous researchers have compared and reviewed enrichment factors (EFs) as an index of relative contamination compared to the composition of the Earth's crust (Conko et al, 2004;Duce et al, 1975;García et al, 2006;Wang, 2005). Measured rainfalls with EF values of one to ten are considered to contain loads not significantly different from the crustal elemental composition, whereas precipitations with EF values of ten to 100 are thought to be more heavily loaded, relative to the chemical composition of the crust.…”

“…Measured rainfalls with EF values of one to ten are considered to contain loads not significantly different from the crustal elemental composition, whereas precipitations with EF values of ten to 100 are thought to be more heavily loaded, relative to the chemical composition of the crust. EF values greater than 100 represent high concentrations of heavy metals caused by severe contamination by human activities (Duce et al, 1975;Wang, 2005).…”