Observations of particle number size distributions and new 1 particle formation in six Indian locations 2 3

Abstract

Atmospheric new particle formation (NPF) is a crucial process driving aerosol number concentrations in the atmosphere; it can significantly impact the evolution of atmospheric aerosol and cloud processes. This study analyses at least one year of asynchronous particle number size distributions at six different locations in India. We also analyze the frequency of NPF and its contribution to cloud condensation nuclei (CCN) concentrations. We found that the NPF frequency has a considerable seasonal variability. At the measurement sites analyzed in this study, NPF frequently occurs in March–May (pre-monsoon, about 21 % of the days) and is the least common in October–November (post-monsoon, about 7 % of the days). Considering the NPF events in all locations, the particle formation rate (JNUC) varied by more than an order of magnitude (0.01–0.6 cm−3 s−1) and the growth rate (GRNUC) by about three orders of magnitude (0.2–17.2 nm h−1). We found that JNUC was higher by nearly an order of magnitude during NPF events in urban areas than mountain sites. GRNUC did not show a systematic difference. Our results showed that NPF events could significantly modulate the shape of particle number size distributions and CCN concentrations in India. The contribution of a given NPF event to CCN concentrations was the highest in urban locations (4.3 × 103 cm−3 per event and 1.2 × 103 cm−3 per event for 50 nm and 100 nm, respectively) as compared to mountain-background sites (2.7 × 103 cm−3 per event and 1.0 × 103 cm−3 per event). To better understand atmospheric NPF and its contribution to CCN concentrations, we would need long-term observational data from various diverse environments in India, aided with regional model simulations to help interpret field observations.