Articles | Volume 16, issue 15
Atmos. Chem. Phys., 16, 9805–9830, 2016
Atmos. Chem. Phys., 16, 9805–9830, 2016

Research article 04 Aug 2016

Research article | 04 Aug 2016

Fluorescent biological aerosol particle measurements at a tropical high-altitude site in southern India during the southwest monsoon season

A. E. Valsan1, R. Ravikrishna2, C. V. Biju3, C. Pöhlker4, V. R. Després5, J. A. Huffman6, U. Pöschl7, and S. S. Gunthe1 A. E. Valsan et al.
  • 1EWRE Division, Department of Civil Engineering, Indian Institute of Technology Madras, Chennai, 600 036, India
  • 2Department of Chemical Engineering, Indian Institute of Technology Madras, Chennai, 600 036, India
  • 3Department of Civil Engineering, College of Engineering Munnar, PB.No:45, County Hills, Munnar, 685612, India
  • 4Biogeochemistry Department, Max Planck Institute for Chemistry, P.O. Box 3060, Mainz, Germany
  • 5Institute of General Botany, Johannes Gutenberg University, Mainz, Germany
  • 6Department of Chemistry and Biochemistry, University of Denver, 2190 E. Iliff Ave., Denver, CO, 80208, USA
  • 7Multiphase Chemistry Department, Max Planck Institute for Chemistry, P.O. Box 3060, Mainz, Germany

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.

Final-revised paper