Carbon isotope‐constrained seasonality of carbonaceous aerosol sources from an urban location (Kanpur) in the Indo‐Gangetic Plain

Abstract

The Indo‐Gangetic Plain (IGP) in northern India, Pakistan, and Bangladesh is a major source of carbonaceous aerosols in South Asia. However, poorly constrained seasonality of their sources over the IGP leads to large uncertainty in climate and health effects. Here we present a first data set for year‐round radiocarbon (Δ14C) and stable carbon (δ13C)‐based source apportionment of total carbon (TC) in ambient PM10 (n = 17) collected from an urban site (Kanpur: 26.5°N, 80.3°E) in the IGP during January 2007 to January 2008. The year‐round 14C‐based fraction biomass (fbio‐TC) estimate at Kanpur averages ~77 ± 7% and emphasizes an impact of biomass burning emissions (BBEs). The highest fbio‐TC (%) is observed in fall season (October–November, 85 ± 6%) followed by winter (December–February, 80 ± 4%) and spring (March–May, 75 ± 8%), while lowest values are found in summer (June–September, 69 ± 2%). Since biomass/coal combustion and vehicular emissions mostly contribute to carbonaceous aerosols over the IGP, we predict δ13CTC (δ13Cpred) over Kanpur using known δ13C source signatures and the measured Δ14C value of each sample. The seasonal variability of δ13Cobs − δ13Cpred versus Δ14CTC together with air mass back trajectories and Moderate Resolution Imaging Spectroradiometer fire count data reveal that carbonaceous aerosols in winter/fall are significantly influenced by atmospheric aging (downwind transport of crop residue burning/wood combustion emissions in the northern IGP), while local sources (wheat residue combustion/vehicular emissions) dominate in spring/summer. Given the large temporal and seasonal variability in sources and emission strength of TC over the IGP, 14C‐based constraints are, thus, crucial for reducing their uncertainties in carbonaceous aerosol budgets in climate models.

A Climatological Satellite Assessment of Absorbing Carbonaceous Aerosols on a Global Scale

“…The relatively high frequencies of ACA over these regions are related either to biomass burning, more specifically burning of agricultural residues and grassland, that take place from winter through to spring [117,118] or to other anthropogenic activities like coal combustion, [119]. The strong presence of ACA over South Asia, especially over the Indo-Gangetic plain, is well documented in literature and plays an important role for south Asian climate and hydrological cycle [120,121].…”

Source apportionment of carbonaceous aerosols in Xi'an, China: insights from a full year of measurements of radiocarbon and the stable isotope <sup>13</sup>C

“…Different emission sources have their own source signature: carbonaceous aerosol from coal combustion is enriched in 13 C (i.e., has higher δ 13 C values of ∼ −25 ‰ to −21 ‰) compared to aerosol from liquid fossil fuel combustion (δ 13 C ∼ −28 ‰ to −24 ‰) and from burning of C 3 plants (δ 13 C ∼ −35 ‰ to −24 ‰) (Andersson et al, 2015, and references therein). Complementing 14 C source apportionment with 13 C measurements allows a better constraint of the contribution of different emission sources to carbonaceous aerosols (Kirillova et al, , 2014aBosch et al, 2014;Winiger et al, 2015Winiger et al, , 2016Bikkina et al, 2016Bikkina et al, , 2017Yan et al, 2017). For example, EC is inert to chemical or physical transformations; thus the δ 13 C EC preserves the signature of emission sources (L. Huang et al, 2006;Andersson et al, 2015;Winiger et al, 2015Winiger et al, , 2016.…”

Study on Mercury in PM10 at an Urban Site in the Central Indo-Gangetic Plain: Seasonal Variability and Influencing Factors

“…Biomass burning significantly affects regional air quality in the IGP, particularly in the winter (Chen et al, 2017). Major sources of biomass-burning emissions are crop harvesting and the common practice of wood burning for domestic use (Bikkina et al, 2017). Kanpur has a mainly humid subtropical climate characterized by hot summers and cold winters (Ghosh et al, 2014).…”

“…In addition, studies have noted the associations of particulate matter and Hg with health, including cancer, respiratory symptoms, and mortality (Dockery and Pope, 1994;Kumari and Kulshrestha, 2018). In addition to several studies on chemical composition (Ram et al, 2010;Sen et al, 2016;Srivastava et al, 2016), some research has recently been conducted on the isotopic ratio of carbon, both stable 13 C and radiocarbon 14 C, to characterize the sources of carbonaceous aerosols (i.e., biomass burning, coal combustion and other fossil fuels at Delhi (Sawlani et al, 2019), Kanpur (Ghosh et al, 2014;Bikkina et al, 2017) and Lucknow and Varanasi in the IGP region (Sharma et al, 2015(Sharma et al, , 2017Sen et al, 2018). Lead (Pb) isotopic compositions of aerosols have been used to study the combustion of fossil fuel and high-temperature industries to evaluate Pb contamination at Kanpur (Sen et al, 2016).…”