Assessment of PM2.5 and PM10 over Guwahati in Brahmaputra River Valley: Temporal evolution, source apportionment and meteorological dependence

Özet

Temporal evolution, source apportionment and transport pathways of particulate matter (PM2.5 andPM10) are analysed over Guwahati, located in the Brahmaputra River Valley (BRV), as a function ofmeteorological dynamics. During the study period (July 2013eJune 2014), the mean PM2.5 and PM10 massconcentrations were found to be 52 ± 37 and 91 ± 60 mg m3, respectively, both exhibiting higherconcentrations during DecembereMarch and very low during summer. The annual mean ratio of PM2.5/PM10 was 0.57 ± 0.11, varying from 0.24 to 0.86, suggesting dominance of anthropogenic vs naturalemissions during winter and spring, respectively. Diurnal variation reveals higher PM concentrationsduring morning (~9:00 local time (LT)) and evening (~23:00 LT) and lowest around ~14:00 to 17:00 LTdue to influence of dilution processes and higher mixing-layer height over the region. Bivariate plots andConditional Bivariate Probability Function (CBPF) analysis showed that the highest PM2.5 and PM10concentrations are mostly associated with weak northwestern winds (<1.5 ms1) in all seasons exceptspring, when the highest PM10 are for southwestern winds above 4e6 ms1, indicating dust transportfrom SW Asia. Analysis reveals that the local emissions, transported aerosols, along with seasonallychanged air masses, meteorology and boundary-layer dynamics control the concentrations, evolutionand fractions of PM over BRV. The turbid air masses transported over Guwahati mostly from western andsouthwestern directions contribute to higher PM concentrations, either carrying anthropogenic pollutionfrom Indo-Gangetic Plains or locally and LRT dust from BRV and western India, respectively.