Abstract
Accurate information about aerosol particle size distribution and its variation under different meteorological conditions are essential for reducing uncertainties related to aerosol-cloud-climate interaction processes. New particle formation (NPF) and the coagulation significantly affect the aerosol size distribution. Here we study the monthly and seasonal variability of aerosol particle size distribution at Delhi from December 2011 to January 2013. Analysis of aerosol particle size distribution using WRAS-GRIMM reveals that aerosol particle number concentration is highest during the post monsoon season owing to the effect of transported crop residue and biomass burning aerosols. Diurnal variations in number concentration show a bimodal pattern with two Aitken mode peaks in all the seasons. Monthly volume size distribution also shows bi-modal distribution with distinct coarse and fine modes. NPF events are observed less frequently in Delhi. Out of 222 days of WRAS data, only 17 NPF events have been observed, with higher NPF frequency during summer season. Growth rate of the nucleation mode of NPF events vary in the range 1.88–21.66 nm/h with a mean value of ∼8.45 ± 5.73 nm/h. It is found that during NPF events the Aitken and nucleation mode particles contribute more to the number concentration. Simultaneous measurement of UV flux and particulate matter (PM10and PM2.5) have also been done along with particle number size distribution measurement to understand the possible mechanisms for NPF events over the study location.
Highlights
The mode wise analysis of number concentration shows that Aitken mode (30–100 nm) dominates in the study region throughout the year with a maximum mean concentration during the post monsoon season (9.6 × 103 cm−3)
Accumulation and nucleation mode particles are minimal compared to the Aitken mode particles during the entire study period at the sampling site
Nucleation mode particles are high in number than accumulation mode particles during summer and monsoon seasons, whereas accumulation mode particles dominate during the other two seasons in comparison with nucleation mode
Summary
The size distribution of atmospheric aerosol particles are known to have plausible effects on radiation budget through direct interaction (Warner and Twomey, 1967; Liou, 1992; Andreae et al, 2004; Dusek et al, 2006); cloud characteristics by affecting cloud condensation nuclei, CCN (Ramanathan et al, 2001; Andreae et al, 2004) and droplet number density (Rosenfeld et al, 2008; Zhang et al, 2011); visibility (Hand et al, 2002; Bäumer et al, 2008; Singh and Beegum, 2013); communication (Ricklin et al, 2006); human health (Harrison, and Yin, 2000; Valavanidis et al, 2008) and Aerosol Size Distribution and NPF agriculture (Chameides et al, 1999). The climatic and human health implications of aerosol have drawn great attentions in the last 2 decades (Lighty et al, 2000; Bergin et al, 2001; Singh and Dey, 2012; Boucher et al, 2013; Gogoi et al, 2021), there are still scarcity of high-resolution (both spatial and temporal) data on aerosol particle size distribution at distinct geographic parts of the world. While primary sources are dominant contributors to the abundance of atmospheric aerosols, secondary aerosol production is unique in altering aerosol size distribution pattern, changing their dynamical properties. Recent study by Jokinen et al (2017) showed the significance of photochemistry in NPF, by depicting the decrease in UV radiation followed by the decrease in concentration of H2SO4 and nitrogen containing highly oxidized compounds during a partial solar eclipse, resulting in the inhibition of NPF events over the study site
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