Aerosol chemistry, transport, and climatic implications during extreme biomass burning emissions over the Indo-Gangetic Plain

Abstract

Abstract. The large-scale emissions of airborne particulates from burning of agricultural residues particularly over the upper Indo-Gangetic Plain (IGP) have often been associated with frequent formation of haze, adverse health impacts, and modification in aerosol climatology and thereby aerosol impact on regional climate. In this study, short-term variations in aerosol climatology during extreme biomass burning emissions over the IGP were investigated. Size-segregated particulate concentration was initially measured and submicron particles (PM1.1) were found to dominate particulate mass within the fine mode (PM2.1). Particulate-bound water-soluble ions were mainly secondary in nature and primarily composed of sulfate and nitrate. There was evidence of gaseous NH3 dominating neutralization of acidic aerosol species (SO42-) in submicron particles, in contrast to crustal-dominating neutralization in coarser particulates. Diurnal variation in black carbon (BC) mass ratio was primarily influenced by regional meteorology, while gradual increase in BC concentration was consistent with the increase in Delta-C, referring to biomass burning emissions. The influence of biomass burning emissions was established using specific organic (levoglucosan), inorganic (K+ and NH4+), and satellite-based (UV aerosol index, UVAI) tracers. Levoglucosan was the most abundant species within submicron particles (649±177 ng m−3), with a very high ratio (> 50) to other anhydrosugars, indicating exclusive emissions from burning of agriculture residues. Spatiotemporal distribution of aerosol and a few trace gases (CO and NO2) was evaluated using both spaceborne active and passive sensors. A significant increase in columnar aerosol loading (aerosol optical depth, AOD: 0.98) was evident, with the presence of absorbing aerosols (UVAI > 1.5) having low aerosol layer height (∼ 1.5 km). A strong intraseasonality in the aerosol cross-sectional altitudinal profile was even noted from CALIPSO, referring to the dominance of smoke and polluted continental aerosols across the IGP. A possible transport mechanism of biomass smoke was established using cluster analysis and concentration-weighted air mass back trajectories. Short-wave aerosol radiative forcing (ARF) was further simulated considering intraseasonality in aerosol properties, which resulted in a considerable increase in atmospheric ARF (135 W m−2) and heating rate (4.3 K day−1) during extreme biomass burning emissions compared to the non-dominating period (56 W m−2, 1.8 K day−1). Our analysis will be useful to improve understanding of short-term variation in aerosol chemistry over the IGP and to reduce uncertainties in regional aerosol–climate models.

Long-term observation of black carbon aerosols at an urban location over the central Indo-Gangetic Plain, South Asia

“…370, 470, 520, 590, 660, 880 and 950 nm via its filter tape, on which aerosols are deposited through a uniform flow rate. The BC mass concentration corresponding to 370 nm represents BC emissions from biomass burning, while BC measured at the infra-red wavelength (880 nm) was used to represent both fossil fuel and biomass burning emissions Singh et al, 2018). Delta-C was computed as the difference between BC 370 and BC 880 .…”

“…Considering the spectral dependence of carbonaceous aerosols, BC measured at UV range (370 nm) was used as representative of biomass burning emissions, while BC measured at infrared range (880 nm) was used to represent both fossil fuel and biomass burning emissions Singh et al, 2018). Such assumptions have scientific ground, as organic aerosols emitted from biomass burning emissions have higher absorption at UV range than in infrared.…”

“…This contrasts with the former Soviet Union and Middle Asia, where local sources contribute to < 50% of the BC loading, whereas emissions from Europe account almost to 40% of the BC burden . Over South and Southeast Asia, extreme pollution events like agro-residue burning in North India (Rajput et al, 2014a;Singh et al, 2018), peatland burning (like in central Kalimantan) (Stockwell et al, 2016) and celebratory fireworks over India (Kumar et al, 2016a) emit huge carbonaceous aerosols into the atmosphere. As emitted, BC aerosols are mostly hydrophobic (Laborde et al, 2013), having relatively shorter residence time (< 7 days) (Bond et al, 2013) before gradually mixing with water-soluble components through atmospheric aging, and thereby converting into a hydrophilic compound (Riemer et al, 2010).…”

Spatiotemporal Trends of Aerosols over Urban Regions in Pakistan and Their Possible Links to Meteorological Parameters

“…The list for generating these aerosols includes anthropogenic and natural sources. Natural aerosols (e.g., dust and sea salt) mostly originate from the southern dry regions and the nearby ocean [16,17], while anthropogenic aerosols originate mainly from vehicular and industrial emissions [18][19][20][21]. Dust lifted from the Thar desert, as a result of dust storms during the pre-monsoon season may be associated with increased dust concentration over the Indo-Gangetic-Plane (IGP) [22].…”

Comparing a Range of Simple Plume Rise Models and Misr Aerosol Height Measurements

“…The observed air pollution in a region is the combination of these various different local and remotely transported sources (Cohen et al 2011, Tosca et al 2011. A clear understanding of the impacts of these various sources is complex in regions where there are multiple significant sources, since they occur across different spatial and temporal scales: urban sources near the surface and biomass burning sources high in the atmosphere (Singh et al 2018).…”