Seasonal variability in chemical composition and oxidative potential of ambient aerosol over a high altitude site in western India

The role of particulate matter (PM) has been well documented in causing cardiopulmonary diseases because they are redox active and generate reactive oxygen species (ROS) in situ in the human body. Capacity of PM to catalyze in situ formation of ROS is known as their oxidative potential (OP). However, studies on OP of PM over different regions are scarce. PM10 samples were collected over Mount Abu (24.6 degrees N, 72.7 degrees E, 1680m asl), India, from March 2014 to May 2016. These samples were analyzed for carbonaceous aerosol, major ions and dithiothreitol (DTT)-based OP. All the data were classified into four seasons (winter, spring, pre-monsoon, and post-monsoon) based on prevailing meteorological conditions. Seasonally averaged (+/- 1 sigma) volume-normalized OP (OPv) were 0.76 +/- 0.52, 1.44 +/- 0.48, 1.04 +/- 0.57, and 1.69 +/- 0.80 nmol DTT min(-1)m(-3), and mass-normalized OP (OPm) were 14 +/- 8, 14 +/- 7, 10 +/- 7, and 23 +/- 9 pmol DTT min(-1) mu g(-1) during winter, spring, pre-monsoon and post-monsoon, respectively. Observed OPv (nmol DTT min(-1) m(-3)) values (0.09-3.04) are somewhat higher than those documented over Los Angeles (0.10-0.16) and Beijing (0.10-0.49), and similar to those reported over Orinda (0.37-2.50) and Patiala (1.3-7.2). The highest OPm and OPv values found during post-monsoon were attributed to long-range transport of anthropogenically emitted pollutants brought by the northeasterly (NE) air-masses. It is inferred that the source(s) emitting elemental carbon also emit other species, which are more DTT-active than those species which are emitted along with anthropogenically derived inorganic species. Our results also infer that OPv varies but OPm do not vary drastically from region to region. This observation has broader implications in assessing the effects of aerosol on human health on regional/global scale. (c) 2018 Elsevier B.V. All rights reserved.