Aerosol temporal characteristics and its impact on shortwave radiative forcing at a location in the northeast of India

Abstract

[1] Measurements of aerosol optical depth (AOD) and mass concentration of composite and black carbon (BC) aerosols made with collocated instruments over Dibrugarh in Northeast India are used to estimate the aerosol radiative forcing for the period June 2008 to May 2009. AOD shows seasonal variation with maximum in premonsoon (0.69 ± 0.13 at 500 nm in March 2009) and minimum in the retreating monsoon (0.08 ± 0.01 at 500 nm in October 2008). Ångström coefficients a and b are highest in monsoon and premonsoon season and are lowest in premonsoon and retreating monsoon, respectively. The size segregated mass concentration is minimum in the monsoon season for all the three modes nucleation, accumulation, and coarse and maximum in winter for accumulation and coarse and in premonsoon for nucleation mode. The BC mass concentration is highest 16.3 ± 1.4 mg m −3 in winter and lowest 3.4 ± 0.9 mg m −3 in monsoon. The estimated aerosol radiative forcing of the atmosphere, using Optical Properties of Aerosols and Clouds (OPAC) outputs as inputs for Santa Barbara Discrete Ordinate Atmospheric Radiative Transfer (SBDART), is maximum in premonsoon followed by that in winter and minimum in retreating monsoon. Negative forcing is observed at the surface, whereas the top of the atmosphere (TOA) forcing is nearly zero in retreating monsoon and is negative in rest of the seasons. The forcing efficiency and heating rate were highest during winter and premonsoon, respectively.

Temporal changes of particulate concentration in the ambient air over the city of Zahedan, Iran

“…Similar annual variations of the anthropogenic aerosols have been observed within urban environments in India (Badarinath et al, 2009;Ramachandran and Kedia, 2010;Pathak et al, 2010). In addition, the boundary layer mixing height is lower in winter and traps the pollutants near the ground as a result of temperature inversions.…”

“…The similarity between diurnal PM 10 variations recorded in this study during autumn and winter and those recorded over several Indian cities (e.g. Madhavan et al, 2008;Pathak et al, 2010) suggests that local anthropogenic emissions and vertical mixing in the boundary layer play a major role in controlling diurnal PM concentrations. During spring no clear pattern in PM 10 diurnal variation is observed since several peaks and gaps occur.…”

Environmental monitoring of surface ozone and other trace gases over different time scales: chemistry, transport and modeling

“…These peaks are mainly attributed to vehicular traffic emissions. Gradual increase in BC concentrations after evening hours (17:00) was observed from domestic activities (Pathak et al 2010) and surface-based inversion (Ganguly et al 2006). The decrease in BC concentration in midnight hours is due reduction in traffic density and sedimentation (02:00-05:00 h).…”

“…High mean BC values in winter were due to entrapment of pollutant emissions in the shallow boundary layer. In addition, meteorological parameters such as low temperature and calm winds localize the pollutant concentration (Pathak et al 2010). In monsoon, low values were recorded due to scavenging effect of rainfall (Kumar et al 2011) and also due to mechanical turbulence of wind shear (Babu et al 2002).…”

Contrasting aerosol characteristics and radiative forcing over Hyderabad, India due to seasonal mesoscale and synoptic‐scale processes

“…The algorithm is known for its reliability and its computational efficiency for solving the radiative transfer equations and has been extensively used over different locations in India (e.g. Satheesh et al, 2002;Vinoj et al, 2004;Ramachandran et al, 2006;Moorthy et al, 2009;Pathak et al, 2010;Ramachandran and Kedia, 2010; among many others). The ARF calculations were performed in the short-wave (0.3-4.0 µm) solar spectrum, while the diurnally-averaged ARF values are used to compute the monthly means.…”