Abstract. An ultraviolet aerodynamic particle sizer (UV-APS) was continuously operated for the first time during two seasons to sample the contrasting winds during monsoon and winter to characterize the properties of fluorescent biological aerosol particles (FBAPs), at a high-altitude site in India. Averaged over the entire monsoon campaign (1 June–21 August 2014), the arithmetic mean number and mass concentrations of coarse-mode (> 1 µm) FBAPs were 0.02 cm−3 and 0.24 µg m−3, respectively, which corresponded to ∼ 2 and 6 % of total aerosol loading, respectively. Average FBAP number size distribution exhibited a peak at ∼ 3 µm, which is attributed to the fungal spores, as supported by scanning electron microscope (SEM) images, and these results are consistent with previous studies made for FBAPs. During 11 weeks of measurements the variability of the total coarse-mode particle number (TAP) concentration was high compared to that observed in FBAP number concentrations. The TAP and FBAP number concentrations measured at this site were strongly dependent on changes in wind direction and rainfall. During periods of westerly/southwesterly winds with heavy persistent rainfall, the TAP and FBAP concentrations exhibited very low values (1.3 and 0.005 cm−3, respectively) with no significant diurnal variations, whereas during periods of northerly winds with scattered rainfall FBAPs exhibited relatively high concentration values (0.05 cm−3) with pronounced diurnal variations, which were strongly coupled with diurnal variations in meteorological parameters. The campaign-averaged FBAP number concentrations were shown to correlate with daily patterns of meteorological parameters and were positively correlated with relative humidity (RH; R2 = 0.58) and negatively with temperature (R2 = 0.60) and wind speed (R2 = 0.60). We did not observe any significant positive correlation with precipitation as reported by previous researchers from selected areas. These measurement results confirm the fact that the ratio of PBAPs to TAP is strongly dependent on particle size and location and thus may constitute a significant proportion of total aerosol particles.
Abstract. Persistent organic pollutants that have accumulated in soils can be
remobilised by volatilisation in response to chemical equilibrium with the
atmosphere. Clean air masses from the Indian Ocean, advected with the onset
of the summer monsoon, are found to reduce concentrations of
hexachlorocyclohexane (HCH), dichlorodiphenyltrichloroethane (DDT) and its
derivatives, endosulfan and polychlorinated biphenyls (PCBs) in air at a
mountain site (all in the range 5–20 pg m−3) by 77 %, 70 %, 82 % and 45 %,
respectively. The analysis of fugacities in soil and air suggest that the
arrival of summer monsoon triggers net volatilisation or enhances ongoing
revolatilisation of the now-banned chemicals HCH and PCBs from
background soils in southern India. The response of the air–soil exchange was
modelled using a regional air pollution model, WRF-Chem PAH/POP. The results
suggest that the air is increasingly polluted during transport by the
south-westerly monsoon winds across the subcontinent. Using a multidecadal
multimedia mass balance model, it is found that air–surface exchange of HCH
and DDT have declined since the ban of these substances from agriculture, but
remobilisation of higher chlorinated PCBs may have reached a historical
high, 40 years after peak emission.
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