Aerosol–Cloud Interaction: A Case Study

MODerate Resolution Imaging Spectroradiometer (MODIS) retrieved aerosol and cloud products at the nine selected stations over Western Himalayan and Deccan Plateau regions were inferred to bring out their salient features and to investigate aerosol–cloud interaction. Annually, Ångström exponent (AE) decreases with aerosol optical depth (AOD) while in winter it increases with AOD at most of the stations. Results bring out positive and/or negative association between AOD and almost all the cloud parameters over the selected stations. Aerosol indirect effect (AIE) is quantified for fixed liquid water path (LWP) bins ranging from 1 to 350 g/m2 at an interval of 25 g/m2 for three categories of stations, viz., CAT‐H, CAT‐M, and CAT‐L based on heavy, moderate, and low aerosol loading, respectively. AIE is negative at CAT‐H (−0.04 ± 0.14), while it is positive at CAT‐M (0.01 ± 0.07) and CAT‐L (0.10 ± 0.48). During winter, negative AIE has been observed for all three categories. In pre‐monsoon, the majority of LWP bins (86% at CAT‐H and 60% at CAT‐M) showed positive AIE, while about 71% of LWP bins indicted negative AIE at CAT‐L. However, during monsoon about 63–71% of LWP bins showed negative AIE at these categories. Study elucidates the influence of factors like cloud type, cloud dynamics/thermodynamics on aerosol–cloud interactions

Characteristics of Surface Ozone Levels at Climatologically and Topographically Distinct Metropolitan Cities in India

Abstract Surface ozone (O3) data at Pune (1998–2014) and Delhi (1998–2013) are studied to examine their temporal characteristics. Study also examines role of meteorology and atmospheric boundary layer height (ABLH) in modulating surface O3 at these sites. Using diurnal variability of surface O3, rate of change of surface O3, [d(O3)/dt] is estimated to infer the nature of surface O3 formation/destruction mechanisms. Analysis of data reveals that at both locations, surface O3 concentrations during daytime are significantly high as compared to those during nighttime. Seasonally, at Pune averaged daytime surface O3 concentrations are high during pre-monsoon and low in monsoon while those during winter and post-monsoon are found to be significantly higher than those in monsoon but half as compared to those in pre-monsoon. At Delhi, averaged daytime surface O3 concentration is minimum in winter and maximum in pre-monsoon with monsoon and post-monsoon values being about 0.79–0.82 times with respect to pre-monsoon O3 concentrations. High natural/anthropogenic pollutant concentration, abundance of ozone precursor gases, high temperature and high rate of photo-oxidation of precursor gases due to solar flux are the causal factors for increased surface O3 concentrations in pre-monsoon season. Reduced solar flux decreases photo-dissociation of ozone precursor gases resulting in low O3 concentration during winter season. Occurrence of low surface O3 during early morning hours in monsoon, post-monsoon and winter seasons is because of low ABLH and low stratosphere-troposphere exchange (STE). [d(O3)/dt] values during morning/evening at Pune and Delhi are indicative of asymmetric and symmetric nature of ozone formation/destruction mechanisms