Link between local scale BC emissions in the Indo-Gangetic Plains and large scale atmospheric solar absorption

Atmos. Chem. Phys., 12, 1173–1187, 2012 www.atmos-chem-phys.net/12/1173/2012/ doi:10.5194/acp-12-1173-2012 © Author(s) 2012. CC Attribution 3.0 License. Atmospheric Chemistry and Physics Link between local scale BC emissions in the Indo-Gangetic Plains and large scale atmospheric solar absorption P. S. Praveen1 , T. Ahmed1 , A. Kar2 , I. H. Rehman2 , and V. Ramanathan1 1 Center for Clouds, Chemistry and Climate, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Drive, MC 0221, La Jolla, CA 92093-0221, USA 2 The Energy and Resources Institute, Darbari Seth Block, IHC Complex, Lodhi Road, New Delhi, 110003, India Correspondence to: V. Ramanathan () Received: 7 June 2011 – Published in Atmos. Chem. Phys. Discuss.: 28 July 2011 Revised: 9 December 2011 – Accepted: 5 January 2012 – Published: 30 January 2012 Abstract. Project Surya has documented indoor and outdoor concentrations of black carbon (BC) from traditional biomass burning cook stoves in a rural village located in the Indo-Gangetic Plains (IGP) region of N. India from November 2009–September 2010. In this paper, we systematically document the link between local scale aerosol properties and column averaged regional aerosol optical properties and atmospheric radiative forcing. We document observations from the first phase of Project Surya and estimate the source dependent (biomass and fossil fuels) aerosol optical properties from local to regional scale. Data were collected using surface based observations of BC, organic carbon (OC), aerosol light absorption, scattering coefficient at the Surya village (SVI 1) located in IGP region and integrated with satellite and AERONET observations at the regional scale (IGP). The daily mean BC concentrations at SVI 1 showed a large increase of BC during the dry season (December to February) with values reaching 35 µg m−3 . Space based LIDAR data revealed how the biomass smoke was trapped within the first kilometer during the dry season and extended to above 5 km during the pre-monsoon season. As a result, during the dry season, the variance in the daily mean single scattering albedo (SSA), the ratio of scattering to extinction coefficient, and column aerosol optical properties at the local IGP site correlated (with slopes in the range of 0.85 to 1.06 and R 2 > 0.4) well with the “IGP AERONET” (mean of six AERONET sites). The statistically significant correlation suggested that in-situ observations can be used to derive spatial mean forcing, at least for the dry season. The atmospheric forcing due to BC and OC exceeded 20 Wm−2 during all months from November to May, supporting the deduction that elimination of cook stove smoke emissions through clean cooking technologies will likely have a major positive impact not only on human health but also on regional climate. 1 Introduction Roughly half of the world’s population relies on solid fuels (wood, animal dung, crop residues and coal) for daily household energy needs. Cooking with these fuels results in the emission of a significant amount of smoke (comprised mainly of black carbon and the condensed fraction of semivolatile organics) due to incomplete combustion. For the most part, cooking is done in the kitchen microenvironment with poor ventilation, which leads to an extensive build-up of smoke; this in turn results in exposure to high levels of particulate matter which causes adverse health effects (Sauvain et al., 2006; Smith et al., 2004; Schwarze et al., 2006). This indoor smoke escapes outdoors and leads to atmospheric brown clouds (ABCs) (Ramanathan et al., 2001a). Black carbon (BC), a major component of smoke, strongly absorbs sunlight in the atmosphere and is considered to be the second largest contributor to global warming after CO2 (Ramanathan and Carmichael, 2008; Jacobson, 2010). BC significantly impacts global climate as well as regional climate by perturbing the monsoon circulation and contributing to the retreat of mountain glaciers (Ramanathan et al., 2001a; Lau et al., 2008; Menon et al., 2002, 2010; Flanner et al., 2009; Pettus, 2009). Because of its positive atmospheric radiative forcing (i.e. warming) and relatively short residence time in the atmosphere (few days to weeks) compared to CO2 (lifetime of decades to centuries), reducing BC emissions Published by Copernicus Publications on behalf of the European Geosciences Union. 1174 P. S. Praveen et al.: Biomass cooking and regional solar absorption in India presents unique opportunities for delaying climate change (Ramanathan and Wallack, 2008; Molina et al., 2009; Ramanathan and Xu, 2010). Organic carbon (OC), co-emitted along with BC, was previously known to have negligible solar absorption and thus assumed to have only a cooling effect (Andreae and Gelencser, 2006). However, studies have shown that some OC fractions (referred to as brown carbon) emitted mostly during biomass burning show strong wavelength dependence of absorption in the ultraviolet and visible region (<600 nm) (Kirchstetter et al., 2004), thus adding to positive atmospheric radiative forcing. Biofuel combustion is the predominant source of BC emissions (Tg yr−1 ) over Africa (72 %) and South Asia (68 %) (Reddy and Boucher, 2007). Over India, BC emissions (Gg yr−1 ) from fossil fuel, open burning, and biofuel combustion contribute around 25 %, 33 %, and 42 %, respectively (Venkatraman et al., 2005). Model simulation has shown that replacing traditional methods of cooking (i.e. burning biomass fuel in a mud stove) with improved cook stoves may significantly reduce atmospheric BC burden over South and East Asia (Ramanathan and Carmichael, 2008). The Indo-Gangetic Plain (IGP), situated along the southern edge of the Himalayan region and spanning across the North-Eastern parts of India, is one of the most densely populated regions on the planet. It is characterized by large anthropogenic emissions from rural households, thermal power plants and industries, causing a widespread layer of ABCs over the region (Ramanathan and Ramana, 2005), as revealed by MODIS aerosol optical depth for the IGP region (Fig. 1). Project Surya is the first field study designed to examine the potential of mitigating biomass BC emissions for slowing down global warming and for reducing negative health effects (Ramanathan and Balakrishnan, 2007). The first (or pilot) phase of Project Surya was started in October 2009 in a rural village located in the IGP region of Northern India. The first phase observations were devoted to baseline measurements of BC concentration and aerosol optical properties from both indoors and outdoors. This is the third in a series of four papers on the first phase study. The first paper (Ramanathan et al., 2011) dealt with a cell-phone based BC monitoring system for large scale (e.g. 100–300 households) measurements. The second paper (Rehman et al., 2011) explored the link between indoor and outdoor BC concentration. The fourth paper (Kar et al. (...truncated)