Observations of new particle formation at two distinct Indian subcontinental urban locations

Abstract

While the formation of new atmospheric aerosol particles and their subsequent growth have been observed under diverse environmental conditions globally, such observations are very scarce over Indian subcontinent. Here, we present the systematic analysis for new particle formation (NPF) from two distinct urban locations in India during April–May of two consecutive years. Particle size distributions were measured at Pune (18.53°N, 73.85°E) during 16 April–23 May, 2012 and at Kanpur (26.46°N, 80.32°E) during 16 April–23 May, 2013. The campaign mean total particle number concentration in the similar size range of 4–135 nm at Pune (12.2 × 103 cm−3) was higher than at Kanpur (7.9 × 103 cm−3), whereas the estimated total condensation sink (CS4–750) at Pune (16.2 × 10−3 s−1) was lower than at Kanpur (33.3 × 10−3 s−1). Despite lower particle number concentrations at Kanpur, larger particle sizes resulted in higher condensation sink than at Pune. The mean particle mode diameter at Kanpur was found larger by a factor of ∼1.8 than at Pune. NPF events were observed commonly at both sites, with lower frequency at Kanpur (14%) than that at Pune (26%). The derived particle growth rates, GR, and the formation rates of 5 nm particles, J5, ranged from 3.4 to 13.3 nm h−1 and 0.4 to 13.9 cm−3 s−1, respectively, which are generally comparable to typical values reported in previous studies. Generally, the particle growth rates were found higher at Kanpur, whereas the formation rates were higher at Pune. It appears that the presence of pre-existing large particles at Kanpur than at Pune suppressed formation rates and favored particle growth. Overall, NPF occurred at lower condensation sink, lower RH, higher solar radiation, and higher temperature.