Aerosol climatology at Delhi in the western Indo‐Gangetic Plain: Microphysics, long‐term trends, and source strengths

Abstract

[1] We present the climatology of aerosol microphysics, its trends, and impact of potential sources based on the long term measurements (for a period of 11.5 years from December 2001 to May 2012) of aerosol optical depths (AOD) in the spectral range 340-1020 nm from an urban center Delhi (28.6 N, 77.3 E, 238 m mean sea level) in the western Indo-Gangetic Plain (IGP). The study is the first ever long-term characterization of aerosols over the western IGP from the ground-based measurements. AODs are known to affect the air quality, visibility, radiative balance, and cloud microphysics of the region and IGP is one of the highest populated and polluted regions of the world. Our measurements show consistently high AOD during the entire period of observation. The seasonal variations of spectral AODs and Angstrom parameters are generally consistent every year. The AODs show a weak but statistically significant (in 95% confidence level) decreasing trend approximately À0.02/year at 500 nm, possibly, modulated by the pre-monsoon heavy dust loading during the first half of the observation period. The climatological monthly mean AOD at shorter wavelengths peaks twice, during June and November, while at longer wavelengths it shows only one peak in June. The annual variations of Angstrom exponent, a and its derivative, a′ suggest the prevalence of multi-modal aerosol size distributions at Delhi. The coarse-mode aerosols dominate during summer (March-June) and monsoon (July-September) seasons, whereas fine/accumulation mode enhances during post-monsoon (October-November) and winter (December-February) seasons. Potential advection pathways have been identified using concentration weighted trajectory (CWT) analysis of the 5 day isentropic air mass back trajectories at the observation site and their seasonal variations are discussed.

Estimation of Aerosol Characteristics and Radiative Forcing during Dust Events over Dehradun

“…(Fig. 4(a)) over DDN has been found to be similar to the long period climatology studies over Kanpur (Wang et al, 2011) and Delhi (Lodhi et al, 2013), which indicates the characteristics of IGP sites. This pattern illustrates the impact of dust activities over the site during late premonsoon (May).…”

Quantitative assessment of AOD from 17 CMIP5 models based on satellite-derived AOD over India

“…Hence, the accuracy of MODIS-derived AOD is understood over several, though not all, locations of India. In addition, aerosol properties have been studied over India using a variety of in situ and remote-sensing measurements (Sagar et al, 2004;Dey et al, 2005;Devara et al, 2005;Ganguly et al, 2006;Krishna Moorthy et al, 2007;Srivastava et al, 2008;Kuniyal et al, 2009;Kaskaoutis et al, 2009;Vinoj et al, 2009;Pathak et al, 2010;Niranjan et al, 2011;Kumar et al, 2012;Lodhi et al, 2013;Verma et al, 2014). The aerosol scenario over India, study of anthropogenic and natural aerosols (Verma et al, 2011;Ramachandran et al, 2012), identification of pollution hot-spots (Di Girolamo et al, 2004), and the evolution and increase and/or decrease of pollution levels (Krishna over different timescales have also been studied.…”

Satellite-Based Estimates of Aerosol Washout and Recovery over India during Monsoon

“…One of the notable features of aerosol distribution over India is the high AOD during the monsoon season as observed by satellites (e.g., Ramachandran and Cherian, 2008;Dey and Di Girolamo, 2010) and ground-based measurements (e.g., Singh et al, 2004;Dey and Tripathi, 2008;Lodhi et al, 2013). Precipitation scavenging has been known as an effective removal mechanism of aerosol load from the atmosphere (Loosmore and Cederwall, 2004).…”