Role of South Asian outflow on the oxidative potential of marine aerosols over the Indian Ocean.

Oxidative potential (OP) of fine marine aerosols (PM2.5) over the northern Indian Ocean (N_IO) and equatorial Indian Ocean (E_IO) were studied using shipborne measurements conducted as part of the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB-2018). During the study, an enhanced concentration of PM2.5 was found over N_IO (27.22 ± 14.29 µg.m-3) compared with E_IO (15.91 ± 2.58 µg.m-3), as N_IO experiences continental outflow from anthropogenically dominated South Asian region. However, E_IO received pristine air masses from the middle of the Arabian Sea, implying a reduced concentration. The OP of PM2.5 was evaluated using a dithiothreitol (DTT) assay. The mass (DTTm or intrinsic OP) and volume (DTTv or extrinsic OP) normalized DTT exhibited a significant spatial variation over the Indian Ocean (IO). Intrinsic OP showed ∼2 times higher values over N_IO than E_IO, indicating aging of aerosols during long-range transport impacts OP of marine aerosol. Similarly, increased concentrations of anthropogenic species such as non-sea sulfate (nssSO42-), nitrate (NO3-), ammonium (NH4+), non-sea potassium ion (nssK+), water-soluble transition metals (Fe, Ti, Zn, Cu, Mn, Cr), elemental carbon (EC), organic carbon (OC), water-soluble organic carbon (WSOC), were also observed over N_IO compared with E_IO. Pearson correlation and multiple linear regression (MLR) analysis revealed that combustion sources, chemical processing and co-transportation of anthropogenic species during long-range transport are the main drivers of intrinsic OP in the outflow region.

Evaluating the filtration efficiency of commercial facemasks' materials against respiratory aerosol droplets.

Respiratory droplets serve as a viable transmission mechanism for many viruses and other pathogens. Facemasks are commonly used to minimize the risk of this transmission. However, information on the size-resolved filtration efficiency of commonly available commercial facemasks is not readily available in the literature. To fill this gap, the current study performs aerosolized chamber experiments to evaluate the filtration efficiencies of commonly available commercial facemasks' materials in a size range of 0.3-10 µm. Results rank the performance of filtration through commercial facemasks' materials as follows (values in brackets indicate the average filtration efficiencies across 0.3-10 µm): 6-Layer N95 mask (0.918) > N95 mask - without valve (0.88) > KN95 mask (0.84) > N95 mask -with valve (0.834) > Heavy knitted cotton mask (0.808) > Surgical mask (0.778) > Cotton mask-2 layers (0.744) > Nylon fabric mask-2 layers (0.740) > T-shirt fabric mask-2 layers (0.708) > T-shirt fabric mask-1 layer (0.648). The size-resolved filtration efficiencies through the material across the evaluated commercial facemasks ranged from 38-83% in the size range of 0.3-0.5 µm, 55-88% in the size range of 0.5-1 µm, 69-93% in the size range of 1-2.5 µm, 76-96% in the size range of 2.5-5 µm, and 86-99% in the size range of 5-10 µm. Subsequently, the filtration efficiencies of materials post washing (with detergent in warm water and allowing to dry completely) were also evaluated. The average reduction in filtration efficiencies post washing are as follows: 6-Layer N95 mask: 3%, N95 mask - without valve: 2%, KN95 mask: 4%, N95 mask -with valve: 3%, Heavy knitted cotton mask: 4%, Surgical mask: 18%, Cotton mask-2 layers: 11%, Nylon fabric mask-2 layers: 6%, T-shirt fabric mask-2 layers: 6%, T-shirt fabric mask-1 layer: 8%. This decrease in the filtration efficiency was more pronounced for the sub-micron particles than the super-micron ones.Implications: Facemasks are commonly used to minimize the risk of pathogens through ambient air transmission. However, information on the size-resolved filtration efficiency of commonly available commercial facemasks materials is not readily available in the literature. To fill this gap, the current study performs aerosolized chamber experiments to evaluate the filtration efficiencies of commonly available commercial facemasks materials in a size range of 0.3-10 µm. The performance of the commercial facemasks materials as follows in the order of (values in brackets indicate the average filtration efficiencies across 0.3-10 µm): 6-Layer N95 mask (0.918) > N95 mask - without valve (0.88) > KN95 mask (0.84) > N95 mask -with valve (0.834) > Heavy knitted cotton mask (0.808) > Surgical mask (0.778) > Cotton mask-2 layers (0.744) > Nylon fabric mask-2 layers (0.740) > T-shirt fabric mask-2 layers (0.708) > T-shirt fabric mask-1 layer (0.648). The choice of facemask is greatly driven by the size of viable respiratory droplets that need to be eliminated. If droplets with particle size less than 0.5 µm are required to be filtered, N95 masks without the valve or more layers are preferred. If the primary objective is to filter particles between 0.5-1 µm, then N95 (both with or without valves) or KN95 masks are recommended. Surgical masks and heavy knitted cotton masks may also be used for this purpose, but with caution.

A study on variation of atmospheric pollutants over Bhubaneswar during imposition of nationwide lockdown in India for the COVID-19 pandemic.

The nationwide lockdown in India to flatten the pandemic COVID-19 curve has resulted in the reduction of anthropogenic emission sources to a great extent. This study reports change in air quality and its impact on the environment during the unique lockdown scenario at Bhubaneswar, a coastal smart city in east India. The urban air shows a remarkable reduction in the mean pollutant levels influenced by traffic emission viz. NOx (~ 67 %) and BC (~ 47 %) during lockdown over the pre-lockdown. Comparatively, a lower reduction of CO (~ 14 %) is attributed to the dominance of natural atmospheric chemical regulation and biogenic sources in addition to anthropogenic contributions. In addition to the lockdown, frequent rain events due to depression in the Bay of Bengal (BoB) also had a significant role in the reduction of the primary pollutants over the study site. An enhancement of secondary pollutant viz. O3 (~ 3%) with a distinct diurnal pattern was observed during the first phase of lockdown over the pre-lockdown period. An anti-correlation between O3 and NOx during pre-lockdown points to a higher O3 production potential with decreasing NOx. While a reduction in the titration of O3 due to suppression of fresh NO emissions led to accumulation of O3 in the first phase of lockdown, inhibited photochemistry due to cloudy skies as well as reduction in precursors led to lower O3 values during the later phases of lockdown.