Effect of PM_(2.5) chemical constituents on atmospheric visibility impairment

摘要

PM_(2.5) sampling was conducted at a curbside location in Delhi city for summer and winter seasons, to evaluate the effect of PM_(2.5) and its chemical components on the visibility impairment. The PM_(2.5) concentrations were observed to be higher than the National Ambient Air Quality Standards (NAAQS), indicating poor air quality. The chemical constituents of PM_(2.5) (the water-soluble ionic species SO_4~(-2), NO_3~-, Cl~-, and NH_4~+, and carbonaceous species: organic carbon, elemental carbon) were analyzed to study their impact on visibility impairment by reconstructing the light extinction coefficient, b_(ext). The visibility was found to be negatively correlated with PM_(2.5) and its components. The reconstructed b_(ext) showed that organic matter was the largest contributor to b_(ext) in both the seasons which may be attributed to combustion sources. In summer season, it was followed by elemental carbon and ammonium sulfate; however, in winter, major contributions were from ammonium nitrate and elemental carbon. Higher elemental carbon in both seasons may be attributed to traffic sources, while lower concentrations of nitrate during summer, may be attributed to volatility because of higher atmospheric temperatures. Implications: The chemical constituents of PM_(2.5) that majorly effect the visibility impairment are organic matter and elemental carbon, both of which are products of combustion processes. Secondary formations that lead to ammonium sulfate and ammonium nitrate production also impair the visibility.