Final Report Summary - ARCTIC BC14 (SOURCE APPORTIONMENT OF CLIMATE-FORCING BLACK CARBON IN ARCTIC AEROSOLS BY COMPOUND-SPECIFIC RADIOCARBON ANALYSIS)
Black carbon (BC), a highly condensed carbonaceous aerosol released from incomplete combustion of organic matter, is a key component in the assessment of radiative climate forcing. BC is after CO2 the most probably agent of global climate warming. Anthropogenic emissions of carbonaceous aerosols (CA) are in general very high over South and East Asia, being these of special concern for human health and regional climate impacts. Regional effects include weakened monsoons, decreased rainfalls and melting of Himalayan glaciers. Recently has been reported that high pollutant loads originated in the Indian subcontinent reach Himalayas. Glaciers, in a similar way as happens in Arctic, are very vulnerable to airborne BC because of its impact on the albedo of snow and ice, accelerating melting and sensitivity to warming.
Besides BC, another component of CA is organic carbon (OC), traditionally considered as a light scattering particle. However, recent field studies have shown OC to absorb at lower wavelengths. Thus OC, in addition to BC, may also contribute to light absorption and have a positive direct radiative effect on climate. Light absorbing organic aerosol is usually termed brown carbon (BrC). A significant fraction of BrC is water-soluble (WS-BrC), therefore its dissolution into clouds could result in absorbing droplets that affect the cloud absorption and thus contributing to the indirect aerosol climate effects.
Knowledge about BC and BrC sources and their radiative properties is a prerequisite for an effective mitigation of the global climate warming but unfortunately the relative contribution of different combustion sources to these components of CA in the atmosphere is still poorly understood. In general, source apportionment of aerosols is expected to be transcending science and engage key players in supporting local/regional implementation of mitigation measures.
The researcher has been working within the framework of mainly two international projects: CARDEX (Cloud Aerosol Radiative Forcing Dynamics Experiment) and SusKat (Sustainable Atmosphere for the Kathmandu Valley). CARDEX campaign was conducted at the Maldives Climate Observatory at Hanimaadhoo, Republic of the Maldives (MCOH) during March 2012 with the unifying objective of improving the understanding of the semi-direct aerosol climate effect (full details of the CARDEX campaign can be found in http://www-ramanathan.ucsd.edu/files/CARDEX_prop_Jun_20.pdf.). The MCOH is a long-term receptor station for the South Asian outflow because in wintertime is located downwind of the Indian subcontinent (Figure 1). SusKat campaign was conducted at the supersite Bode (Kathmandu, Nepal), forming part of the International Atmospheric Brown Cloud (ABC) project (http://www-abc-asia.ucsd.edu/) during January 2013 aiming to increase basic knowledge on air pollution in the Kathmandu Valley and its possible recirculation to the Himalayas and the free troposphere (Figure 2).
During the project, a source-diagnosis study of BC and water-soluble BrC has been completed for samples collected during the intensive CARDEX campaign at MCOH. Also the optical properties were measured for water-soluble BrC at this site during the campaign. The results establish a greater role for biomass combustion and biogenic sources in the outflow from S Asian than in East Asia. Wintertime WSOC intercepted over the Indian receptor is an aged aerosol and this aging may lead to less light-absorptive water-soluble compounds. There is a manuscript under revision for publication at Journal of Geophysical Research: Atmospheres including these results. Source apportionment of BC in Kathmandu and in Himalayas has been also studied and currently there is one paper in preparation. At the end of the project, major efforts have been devoted to address investigation towards specific molecules such as polycyclic aromatic hydrocarbons (PAHs) and plasticogenic markers. PAHs, as primary organic aerosols, were used to track aerosol aging and light-absorbing capacity during long-range transport in the S Asian outflow. PAHs in the receptor MCOH, the regional Sinhagad and source Bangladesh and N Delhi sites have been investigated for 13C-PAH, isomer ratios and optical properties. A chemical marker for plasticogenic aerosols has been successfully identified in samples from S Asia and feasibility for a further study based on the specific molecular dual-isotope approach has been evaluated.
Figure 1. Map depicting average Aerosol Optical Depth (AOD) during the CARDEX campaign (23 February - 31 March 2012). The locations of the Maldives Climate Observatory at Hanimaadhoo (MCOH) and Delhi are shown. Colored arrows show the predominant BTs differentiated in four different clusters: IGP and Bay of Bengal (dark green), S India (red), Arabian Sea (blue) and S Bay of Bengal (dark yellow).
Figure 2. Regional haze in Himalaya’s foothills on 2 March 2013 (courtesy of Prof. Maheswar Rupakheti)
Besides BC, another component of CA is organic carbon (OC), traditionally considered as a light scattering particle. However, recent field studies have shown OC to absorb at lower wavelengths. Thus OC, in addition to BC, may also contribute to light absorption and have a positive direct radiative effect on climate. Light absorbing organic aerosol is usually termed brown carbon (BrC). A significant fraction of BrC is water-soluble (WS-BrC), therefore its dissolution into clouds could result in absorbing droplets that affect the cloud absorption and thus contributing to the indirect aerosol climate effects.
Knowledge about BC and BrC sources and their radiative properties is a prerequisite for an effective mitigation of the global climate warming but unfortunately the relative contribution of different combustion sources to these components of CA in the atmosphere is still poorly understood. In general, source apportionment of aerosols is expected to be transcending science and engage key players in supporting local/regional implementation of mitigation measures.
The researcher has been working within the framework of mainly two international projects: CARDEX (Cloud Aerosol Radiative Forcing Dynamics Experiment) and SusKat (Sustainable Atmosphere for the Kathmandu Valley). CARDEX campaign was conducted at the Maldives Climate Observatory at Hanimaadhoo, Republic of the Maldives (MCOH) during March 2012 with the unifying objective of improving the understanding of the semi-direct aerosol climate effect (full details of the CARDEX campaign can be found in http://www-ramanathan.ucsd.edu/files/CARDEX_prop_Jun_20.pdf.). The MCOH is a long-term receptor station for the South Asian outflow because in wintertime is located downwind of the Indian subcontinent (Figure 1). SusKat campaign was conducted at the supersite Bode (Kathmandu, Nepal), forming part of the International Atmospheric Brown Cloud (ABC) project (http://www-abc-asia.ucsd.edu/) during January 2013 aiming to increase basic knowledge on air pollution in the Kathmandu Valley and its possible recirculation to the Himalayas and the free troposphere (Figure 2).
During the project, a source-diagnosis study of BC and water-soluble BrC has been completed for samples collected during the intensive CARDEX campaign at MCOH. Also the optical properties were measured for water-soluble BrC at this site during the campaign. The results establish a greater role for biomass combustion and biogenic sources in the outflow from S Asian than in East Asia. Wintertime WSOC intercepted over the Indian receptor is an aged aerosol and this aging may lead to less light-absorptive water-soluble compounds. There is a manuscript under revision for publication at Journal of Geophysical Research: Atmospheres including these results. Source apportionment of BC in Kathmandu and in Himalayas has been also studied and currently there is one paper in preparation. At the end of the project, major efforts have been devoted to address investigation towards specific molecules such as polycyclic aromatic hydrocarbons (PAHs) and plasticogenic markers. PAHs, as primary organic aerosols, were used to track aerosol aging and light-absorbing capacity during long-range transport in the S Asian outflow. PAHs in the receptor MCOH, the regional Sinhagad and source Bangladesh and N Delhi sites have been investigated for 13C-PAH, isomer ratios and optical properties. A chemical marker for plasticogenic aerosols has been successfully identified in samples from S Asia and feasibility for a further study based on the specific molecular dual-isotope approach has been evaluated.
Figure 1. Map depicting average Aerosol Optical Depth (AOD) during the CARDEX campaign (23 February - 31 March 2012). The locations of the Maldives Climate Observatory at Hanimaadhoo (MCOH) and Delhi are shown. Colored arrows show the predominant BTs differentiated in four different clusters: IGP and Bay of Bengal (dark green), S India (red), Arabian Sea (blue) and S Bay of Bengal (dark yellow).
Figure 2. Regional haze in Himalaya’s foothills on 2 March 2013 (courtesy of Prof. Maheswar Rupakheti)
