Meteorological-gaseous influences on seasonal PM_2.5 variability in the Klang Valley urban-industrial environment

Abstract

Abstract. This study attempts to investigate the fine particulate matter (PM2.5) variability in the Klang Valley urban-industrial environment. In total, 94 daily PM2.5 samples were collected during a one-year campaign from August 2011 to July 2012, covering all four seasons. The samples were analysed for various inorganic components and black carbon. The chemical compositions were statistically analysed and the aerosol pattern was characterised using descriptive analysis, correlation matrices, enrichment factors (EF), stoichiometric analysis and chemical mass closure (CMC). For source apportionment purposes, a combination of positive matrix factorisation (PMF) and multi-linear regression (MLR) was employed. Further, meteorological-gaseous parameters were incorporated into each analysis for improved assessment. The results showed that PM2.5 mass averaged at 28 ± 18 μg m−3, 2.8 fold higher than the World Health Organisation (WHO) annual guideline. On a daily basis, the PM2.5 mass ranged between 6 and 118 μg m−3 with 43 % exceedance of the daily WHO guideline. The North-East monsoon (NE) was the only season with < 50 % sample exceedance of the daily WHO guideline. On an annual scale, PM2.5 mass correlated positively with temperature (T) and wind speed (WS) but negatively with relative humidity (RH). With the exception of NOx, the gases analysed (CO, NO2, NO and SO2) were found to significantly influence the PM2.5 mass. Seasonal variability unexpectedly showed that rainfall, WS and wind direction (WD) did not significantly correlate with PM2.5 mass. Further analysis on the PM2.5 / PM10, PM2.5 / TSP and PM10 / TSP ratios reveal that meteorological parameters only greatly influenced the coarse particles (PM > 2.5μm) and less so the fine particles at the site. Chemical composition showed that both primary and secondary pollutants of PM2.5 are equally important, albeit with seasonal variability. The CMC components identified were: black carbon (BC) > secondary inorganic aerosols (SIA) > dust > trace elements (TE) > sea salt > K+. The EF analysis distinguished two groups of trace elements: those with anthropogenic sources (Pb, Se, Zn, Cd, As, Bi, Ba, Cu, Rb, V and Ni) and those with a crustal source (Sr, Mn, Co and Li). The five identified factors resulting from PMF 5.0 were: (1) combustion of engine oil; (2) mineral dust; (3) mixed SIA and biomass burning; (4) mixed traffic and industrial; and (5) sea salt. Each of these sources had an annual mean contribution of 17, 14, 42, 10 and 17 %, respectively. The dominance of each identified source largely varied with changing season and a few factors were in agreement with the CMC, EF and stoichiometric analysis, accordingly. In relation to meteorological-gaseous parameters, PM2.5 sources were influenced by different parameters during different seasons. In addition, two air pollution episodes (HAZE) revealed the influence of local and/or regional sources. Overall, our study clearly suggests that the chemical constituents and sources of PM2.5 were greatly influenced and characterised by meteorological and gaseous parameters which largely vary with season.