Seasonal variability in abundance and diversity of airborne pollen grains in the foothills of the Western Himalayas

Pollen presence in the atmosphere, as Primary Biological Aerosol (PBA) fraction, constitutes a significant proportion of aerosol. In recent years, research focusing on the role of pollen grains in the atmosphere has intensified toward understanding their impacts on environmental processes and human health. Investigation over 15 months, from January 2012 to March 2013, in Jawali, Kangra district of Himachal Pradesh, was undertaken to estimate the abundance and diversity of airborne pollen grains in ambient coarse particulate matter (CPM) sampled using a high-volume PM sampler. The average CPM load of 46.6 µg m⁻³ corresponded with an average pollen concentration of 219 pollen grains m⁻³ during the study. A large diversity of pollen grains in CPM was observed, with 54 different types of pollen grains belonging to 35 plant families, including two gymnosperm families. The major tree genera characterized were Mallotus, Pinus, Eucalyptus, Syzigium, Prosopis, Phyllanthus, Cassia, and Acacia, whereas the shrubs were Dodonaea, Ricinus, and Ephedra. Herbaceous pollen contributed a significant fraction of pollen grains belonging to Poaceae, Asteraceae, Brassicaceae, Cannabaceae, and Urticaceae. A significant number of pollen grains recorded in this investigation have been reported as allergenic in the literature. Most of the pollen grains in CPM belonged to the region's endemic vegetation, suggesting their local origin. The monthly concentration profile of pollen grains displayed significant variation over 15 months. Meteorological parameters, temperature, planetary boundary layer height, and wind speed statistically correlated with CPM. The insignificant correlations with pollen concentration indicated that the sources of CPM and pollen emissions differ. However, pollen showed a weak correlation with wind speed and a negative correlation with relative humidity.