Continental outflow of anthropogenic aerosols over Arabian Sea and Indian Ocean during wintertime: ICARB-2018 campaign

Aswini, A.R.; Hegde, Prashant; Aryasree, S.; Girach, Imran A.; Nair, Prabha R.

doi:10.1016/j.scitotenv.2019.135214

Cited by 47 publications

(29 citation statements)

References 107 publications

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“…Over the northern Indian Ocean enhanced aerosol loading during winter months is mostly due to the presence of fine mode anthropogenic particles (Figs. 1 and Supplementary Figure- 03 ) with major contributions from non-sea salt sulphate (nss- ) and carbonaceous aerosols 31 . Hygroscopicity (κ s ) of nss- is found to be 8–15% lower than pure sodium chloride 32 , while in the case of carbonaceous particles κ s depends on the nature of mixing between organic and inorganic species 33 .…”

Section: Resultsmentioning

confidence: 99%

Anthropogenic emissions from South Asia reverses the aerosol indirect effect over the northern Indian Ocean

Jose

Nair

Babu

2020

Sci Rep

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Atmospheric aerosols play an important role in the formation of warm clouds by acting as efficient cloud condensation nuclei (CCN) and their interactions are believed to cool the Earth-Atmosphere system (‘first indirect effect or Twomey effect’) in a highly uncertain manner compared to the other forcing agents. Here we demonstrate using long-term (2003–2016) satellite observations (NASA’s A-train satellite constellations) over the northern Indian Ocean, that enhanced aerosol loading (due to anthropogenic emissions) can reverse the first indirect effect significantly. In contrast to Twomey effect, a statistically significant increase in cloud effective radius (CER, µm) is observed with respect to an increase in aerosol loading for clouds having low liquid water path (LWP < 75 g m−2) and drier cloud tops. Probable physical mechanisms for this effect are the intense competition for available water vapour due to higher concentrations of anthropogenic aerosols and entrainment of dry air on cloud tops. For such clouds, cloud water content showed a negative response to cloud droplet number concentrations and the estimated intrinsic radiative effect suggest a warming at the Top of the Atmosphere. Although uncertainties exist in quantifying aerosol-cloud interactions (ACI) using satellite observations, present study indicates the physical existence of anti-Twomey effect over the northern Indian Ocean during south Asian outflow.

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Section: Resultsmentioning

confidence: 99%

Anthropogenic emissions from South Asia reverses the aerosol indirect effect over the northern Indian Ocean

Jose

Nair

Babu

2020

Sci Rep

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“…Further, the association between ammonium and sulfate (Fig. S3 in the Supplement) indicated an NH + 4 deficit environment (Aswini et al, 2020). In Fig.…”

Section: Association Between Bc Coating Thickness Andmentioning

confidence: 89%

“…Produced by the incomplete combustion of hydrocarbon fuels, BC has a global direct radiative forcing of +0.71 W m −2 (+0.08 to +1.26 W m −2 ), of which fossil fuel and biofuel emissions contribute +0.51 W m −2 ; the rest is from biomass burning (Bond et al, 2013). Such large forcing due to BC is reported to be capable of causing significant perturbations to atmospheric circulation, cloud dynamics, rainfall pattern, static stability, and convective activity over regional scales, especially over the Indian region (Menon et al, 2002;Ramanathan et al, 2005;Meehl et al, 2008;Bollasina et al, 2008;Lawrence and Lelieveld, 2010;Babu et al, 2011;D'Errico et al, 2015;Boos and Storelvmo, 2016). While fresh BC is fractal-like, hydrophobic, and externally mixed, atmospheric ageing (temporally and/or chemically) results in internally mixed BC with hydrophilic compounds (e.g., organic acids and ammonium sulfate) and an altered mixing state, size, and morphology.…”

Section: Introductionmentioning

confidence: 99%

Mixing state of refractory black carbon aerosol in the South Asian outflow over the northern Indian Ocean during winter

et al. 2021

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Abstract. Regional climatic implications of aerosol black carbon (BC), which has a wide variety of anthropogenic sources in large abundance, are well recognized over South Asia. Significant uncertainties remain in its quantification due to a lack of sufficient information on the microphysical properties (its concentration, size, and mixing state with other aerosol components) that determine the absorption potential of BC. In particular, the information on the mixing state of BC is extremely sparse over this region. In this study, the first observations of the size distribution and mixing state of individual refractory black carbon (rBC) particles in the South Asian outflow to the south-eastern Arabian Sea and the northern and equatorial Indian Ocean regions are presented based on measurements using a single particle soot photometer (SP2) aboard the Integrated Campaign for Aerosols, gases, and Radiation Budget (ICARB-2018) ship during winter 2018 (16 January to 13 February). The results revealed significant spatial heterogeneity of BC characteristics. The highest rBC mass concentrations (∼938±293 ng m−3) with the highest relative coating thickness (RCT; the ratio of BC core to its coating diameters) of ∼2.16±0.19 are found over the south-east Arabian Sea (SEAS) region, which is in the proximity of the continental outflow. As we move to farther oceanic regions, though the mass concentrations decreased by nearly half (∼546±80 ng m−3), BC still remained thickly coated (RCT∼2.05±0.07). The air over the remote equatorial Indian Ocean, which received considerable marine air masses compared to the other regions, showed the lowest rBC mass concentrations (∼206±114 ng m−3) with a moderately thick coating (RCT∼1.73±0.16). Even over oceanic regions far from the landmass, regions that received the outflow from the more industrialized east coast/the Bay of Bengal had a thicker coating (∼104 nm) compared to regions that received outflow from the west coast and/or peninsular India (∼86 nm). Although different regions of the ocean depicted contrasting concentrations and mixing state parameters due to the varied extent and nature of the continental outflow as well as the atmospheric lifetime of air masses, the modal parameters of rBC mass–size distributions (mean mass median diameters ∼ 0.19–0.20 µm) were similar over all regions. The mean fraction of BC-containing particles (FBC) varied in the range of 0.08–0.12 (suggesting significant amounts of non-BC particles), whereas the bulk mixing ratio of coating mass to rBC mass was highest (8.31±2.40) over the outflow regions compared to the remote ocean (4.24±1.45), highlighting the role of outflow in providing condensable material for coatings on rBC. These parameters, along with the information on the size-resolved mixing state of BC cores, throw light on the role of sources and secondary processing of their complex mixtures for coatings on BC under highly polluted conditions. Examination of the non-refractory sub-micrometre aerosol chemical composition obtained using the aerosol chemical speciation monitor (ACSM) suggested that the overall aerosol system was sulfate-dominated over the far-oceanic regions. In contrast, organics were equally prominent adjacent to the coastal landmass. An association between the BC mixing state and aerosol chemical composition suggested that sulfate was the probable dominant coating material on rBC cores.

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“…During this season, north‐easterly winds are persistent and convection over the continental source regions is concealed by large‐scale subsidence, thus restraining the vertical dispersion of pollutants. The studies as part of ICARB‐2018 documented the CCN activity properties of SA outflow over the IO (Nair et al., 2020), bulk chemical composition (Aswini et al., 2020), tropospheric carbon monoxide (CO) distribution (Girach et al., 2020), near‐surface aerosol mass concentrations and its size distributions along with BC mass concentration (Gogoi et al., 2018), and aerosol number size distribution focusing new particle formation events (Kompalli, Nair, et al., 2020). Nevertheless, there are no studies on size‐resolved chemical composition and molecular‐level analysis of OAs over the IO.…”

Section: Introductionmentioning

confidence: 99%

Chemical Characteristics, Size Distributions, Molecular Composition, and Brown Carbon in South Asian Outflow to the Indian Ocean

Boreddy

Hegde

Aswini

et al. 2021

Earth and Space Science

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The transport of south Asian (SA) anthropogenic haze to the Northern Indian Ocean (NIO) is often observed during winter, however, its chemical and molecular constituents are not well explored. To better address this problem, shipborne measurements of size-resolved aerosol sampling were carried out over the northern and equatorial Indian Ocean (EIO) for the quantification of aerosol composition (organic and inorganic) and molecular markers during the winter of 2018. The most striking outcome was the dominance of anthropogenic aerosols derived from biomass-burning and combustion-related emissions over the NIO during the SA outflow.Low level concentrations were noticed over the EIO where oceanic air mass was dominated.Organic carbon (OC), sea-salts (Na + and Cl -), calcium (Ca 2+ ) and nitrates (NO3 -) were enriched in the coarse mode (>2.0 µm) while elemental carbon (EC), water-soluble OC, sulfates (SO4 2-), and potassium (K + ) were abundant in fine mode (<2.0 µm) aerosols. Water-soluble nitrogen aerosols showed a bimodal size distribution with a significant peak in fine mode. The molecular composition of organic aerosols in PM1.1 was characterized by high abundances of sugars and lignin/resin products followed by hydroxy/polyacids and plasticizers. These results underscore that biomass-burning emissions (BBEs), plastic combustions and secondary anthropogenic aerosols are the leading sources of organic aerosols in the SA outflow as further corroborated by the linear-regression analysis between organic and inorganic marker compounds. The mass absorption efficiency of organic (brown carbon; BrC) aerosols (MAEOC-BrC-365nm) was two times higher in SA outflow and largely contributed from BBEs as confirmed by the positive relationship with levoglucosan.

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Continental outflow of anthropogenic aerosols over Arabian Sea and Indian Ocean during wintertime: ICARB-2018 campaign

Cited by 47 publications

References 107 publications

Anthropogenic emissions from South Asia reverses the aerosol indirect effect over the northern Indian Ocean

Anthropogenic emissions from South Asia reverses the aerosol indirect effect over the northern Indian Ocean

Mixing state of refractory black carbon aerosol in the South Asian outflow over the northern Indian Ocean during winter

Chemical Characteristics, Size Distributions, Molecular Composition, and Brown Carbon in South Asian Outflow to the Indian Ocean

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