| 1. |
- Bosch, Carme, et al.
(författare)
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Source-diagnostic dual-isotope composition and optical properties of water-soluble organic carbon and elemental carbon in the South Asian outflow intercepted over the Indian Ocean
- 2014
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Ingår i: Journal of Geophysical Research - Atmospheres. - 2169-897X .- 2169-8996. ; 119:20, s. 11743-11759
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Tidskriftsartikel (refereegranskat)abstract
- The dual carbon isotope signatures and optical properties of carbonaceous aerosols have been investigated simultaneously for the first time in the South Asian outflow during an intensive campaign at the Maldives Climate Observatory on Hanimaadhoo (MCOH) (February and March 2012). As one component of the Cloud Aerosol Radiative Forcing Dynamics Experiment, this paper reports on the sources and the atmospheric processing of elemental carbon (EC) and water-soluble organic carbon (WSOC) as examined by a dual carbon isotope approach. The radiocarbon (C-14) data show that WSOC has a significantly higher biomass/biogenic contribution (865%) compared to EC (594%). The more C-13-enriched signature of MCOH-WSOC (-20.80.7) compared to MCOH-EC (-25.8 +/- 0.3 parts per thousand) and megacity Delhi WSOC (-24.1 +/- 0.9 parts per thousand) suggests that WSOC is significantly more affected by aging during long-range transport than EC. The C-13-C-14 signal suggests that the wintertime WSOC intercepted over the Indian Ocean largely represents aged primary biomass burning aerosols. Since light-absorbing organic carbon aerosols (Brown Carbon (BrC)) have recently been identified as potential contributors to positive radiative forcing, optical properties of WSOC were also investigated. The mass absorption cross section of WSOC (MAC(365)) was 0.5 +/- 0.2 m(2)g(-1) which is lower than what has been observed at near-source sites, indicating a net decrease of WSOC light-absorption character during long-range transport. Near-surface WSOC at MCOH accounted for similar to 1% of the total direct solar absorbance relative to EC, which is lower than the BrC absorption inferred from solar spectral observations of ambient aerosols, suggesting that a significant portion of BrC might be included in the water-insoluble portion of organic aerosols.
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| 2. |
- Budhavant, Krishnakant, et al.
(författare)
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Anthropogenic fine aerosols dominate the wintertime regime over the northern Indian Ocean
- 2018
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Ingår i: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 70
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Tidskriftsartikel (refereegranskat)abstract
- This study presents and evaluates the most comprehensive set to date of chemical, physical and optical properties of aerosols in the outflow from South Asia covering a full winter (Nov. 2014 - March 2015), here intercepted at the Indian Ocean receptor site of the Maldives Climate Observatory in Hanimaadhoo (MCOH). Cluster analysis of air-mass back trajectories for MCOH, combined with AOD and meteorological data, demonstrate that the wintertime northern Indian Ocean is strongly influenced by aerosols transported from source regions with three major wind regimes, originating from the Indo-Gangetic Plain (IGP), the Bay of Bengal (BoB) and the Arabian Sea (AS). As much as 97 +/- 3% of elemental carbon (EC) in the PM10 was also found in the fine mode (PM2.5). Other mainly anthropogenic constituents such as organic carbon (OC), non-sea-salt (nss) -K+, nss-SO42- and NH4+ were also predominantly in the fine mode (70-95%), particularly in the air masses from IGP. The combination at this large-footprint receptor observatory of consistently low OC/EC ratio (2.0 +/- 0.5), strong linear relationships between EC and OC as well as between nss-K+ and both OC and EC, suggest a predominance of primary sources, with a large biomass burning contribution. The particle number-size distributions for the air masses from IGP and BoB exhibited clear bimodal shapes within the fine fraction with distinct accumulation (0.1m0.03. Taken together, the aerosol pollution over the northern Indian Ocean in the dry season is dominated by a well-mixed long-range transported regime of the fine-mode aerosols largely from primary combustion origin.
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| 3. |
- Budhavant, Krishnakant, et al.
(författare)
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Apportioned contributions of PM2.5 fine aerosol particles over the Maldives (northern Indian Ocean) from local sources vs long-range transport
- 2015
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 536, s. 72-78
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Tidskriftsartikel (refereegranskat)abstract
- Urban-like plumes of gases and particulate matter originating from the South Asian region are frequently observed over the Indian Ocean, especially during the dry winter period. However, in addition to the strong sources on main-land South Asia, there are also local Maldivian emissions. The local contributions to the load of fine particulate matter (PM2.5) in the Maldivian capital Male was assessed using the well-established Maldives Climate Observatory at Hanimaadhoo (MCOH) to represent local background, recording the long-range transported component for a full-year synoptic campaign at both sites in 2013. The year-round levels in both Male and MCOH are strongly influenced by the seasonality of the monsoon cycle, including precipitation patterns and air-mass transport pathways, with lower levels during the wet summer season. The annual-average PM2.5 levels in Male are higher (avg. 19 mu g/m(3)) than at MCOH (avg. 13 mu g/m(3)) with the difference being the largest during the summer, when local emissions play a larger role. The 24-hWorld Health Organization (WHO) PM2.5 health guideline was surpassed for the week-long collections in 71% of the cases in Male and in 74% of the cases for Hanimaadhoo. This study shows that in the dry/winter season 90 +/- 11% of PM2.5 levels in Male could be from long-range transport with only 8 +/- 11% from local emissions while in the wet/monsoon season the relative contributions are about equal. The concentrations of organic carbon (OC) and elemental carbon (EC) showed similar seasonal patterns as bulk mass PM2.5. The relative contribution of total carbonaceous matter to bulk mass PM2.5 was 17% in Male and 13% at MCOH, suggesting larger contributions from incomplete combustion practices in the Male local region.
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| 4. |
- Budhavant, Krishnakant B., et al.
(författare)
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Physico-chemical characterization and sink mechanism of atmospheric aerosols over South-west India
- 2020
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Ingår i: Journal of Atmospheric Chemistry. - : Springer Science and Business Media LLC. - 0167-7764 .- 1573-0662. ; 77:1-2, s. 17-33
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Tidskriftsartikel (refereegranskat)abstract
- The properties of the atmospheric aerosols depend on the source region and on the modifications that occur during their transport in the air. We have studied physical and chemical properties of aerosols along with their sink mechanism over two locations in southwest India, an urban site (Pune) and well-established climate observatory at Sinhagad (SINH), which represents rural and high altitude site. The ground-based measurements of aerosols, together with their radiative properties in this study have provided means to understand the observed variability and the impact on the aerosol radiative properties effectively over this region. The annual mean elemental carbon concentration (3.4 mu g m(- 3)) at Pune was observed about three times higher compared to SINH (1.3 mu g m(- 3)), indicating strong emissions of carbon-rich aerosols at the urban location. Aerosol optical properties were derived using the OPAC model which were used to compute the Aerosol radiative forcing (ARF) over both stations calculated using SBDART (Santa Barbara DISORT Atmospheric Radiative Transfer) model shows pronounced seasonal variations due to changes in aerosol optical depth and single scattering albedo at both locations. The year-round ARF was 4-5 times higher over Pune (31.4 +/- 3.5 Wm(- 2)) compared to SINH (7.2 +/- 1.1 Wm(- 2)). The atmospheric heating rate due to aerosols shows a similar pattern as ARF for these locations. The heating was higher in the wintertime, similar to 0.9-1.6 K day(- 1) at Pune, and similar to 0.3-0.6 K day(- 1) at SINH. The estimated scavenging ratio was found high for NO3- and Ca.(2+). The wet deposition fluxes of Cl-, SO42-, Na+, Mg2+ were observed higher for SINH as compared to Pune, due to the high amount of rain received at SINH.
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| 5. |
- Budhavant, Krishnakant, et al.
(författare)
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Black carbon aerosols over Indian Ocean have unique source fingerprint and optical characteristics during monsoon season
- 2023
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 120:8
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Tidskriftsartikel (refereegranskat)abstract
- Effects of aerosols such as black carbon (BC) on climate and buildup of the monsoon over the Indian Ocean are insufficiently quantified. Uncertain contributions from various natural and anthropogenic sources impede our understanding. Here, we use observations over 5 y of BC and its isotopes at a remote island observatory in northern Indian Ocean to constrain loadings and sources during little-studied monsoon season. Carbon-14 data show a highly variable yet largely fossil (65 ± 15%) source mixture. Combining carbon-14 with carbon-13 reveals the impact of African savanna burning, which occasionally approach 50% (48 ± 9%) of the total BC loadings. The BC mass-absorption cross-section for this regime is 7.6 ± 2.6 m2/g, with higher values during savanna fire input. Taken together, the combustion sources, longevity, and optical properties of BC aerosols over summertime Indian Ocean are different than the more-studied winter aerosol, with implications for chemical transport and climate model simulations of the Indian monsoon.
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| 6. |
- Budhavant, Krishnakant, et al.
(författare)
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Changing optical properties of Black Carbon and Brown Carbon aerosols during long-range transport from the Indo-Gangetic Plain to the equatorial Indian Ocean
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Atmospheric aerosols strongly influence the global climate by their light absorption (e.g., black carbon, BC, brown carbon, BrC) and scattering (e.g., sulfate) properties. This study presents simultaneous measurements of ambient aerosol light absorption properties and chemical composition from three large-footprint South Asian receptor sites during the South Asian Pollution Experiment (SAPOEX) in December 2017 - March 2018. The BC mass absorption cross-section (BC-MAC678) values increased from 3.5 ± 1.3 at the Bhola Climate Observatory-Bangladesh (i.e., located at exit outflow of Indo-Gangetic Plain) to 6.4 ± 1.3 at the two regional receptor observatories at Maldives Climate Observatory-Hanimaadhoo (MCOH) and Maldives Climate Observatory-Gan (MCOG), an increase of 80%. This likely reflects a scavenging fractionation resulting in a population of finer BC with higher MAC678 having higher longevity. At the same time, the BrC-MAC365 decreased by a factor of three from the IGP exit to the equatorial Indian Ocean, likely due to photochemical bleaching of organic chromophores. The high chlorine-to-sodium ratio at the near-source-region BCOB suggests a significant contribution of chlorine from anthropogenic activities. This particulate Cl- has the potential to convert into Cl-radicals that can affect the oxidation capacity of the polluted air. Moreover, Cl- is shown to be near-fully consumed during the long-range transport. The results of this synoptic study over the large South Asian scale contribute rare observational constraints on optical properties of ambient BC (and BrC) aerosols over regional scales away from emission sources. It also contributes significantly to understanding the ageing effect of the optical and chemical properties of aerosols as the pollution from the Indo-Gangetic Plain disperses over the tropical ocean.
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| 7. |
- Budhavant, Krishnakant, et al.
(författare)
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Enhanced Light-Absorption of Black Carbon in Rainwater Compared With Aerosols Over the Northern Indian Ocean
- 2020
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Ingår i: Journal of Geophysical Research - Atmospheres. - 2169-897X .- 2169-8996. ; 125:2
-
Tidskriftsartikel (refereegranskat)abstract
- Black carbon (BC) aerosols affect climate, especially in high aerosol loading regions such as South Asia. A key uncertainty for the climate effects of BC is the evolution of light-absorbing properties in the atmosphere. Here, we present a year-round comparison of the mass absorption cross section (MAC; 678 nm) of BC in air (PM10) and rain, for samples collected at the Maldives Climate Observatory at Hanimaadhoo. We develop a filter-loading correction scheme for estimating BC absorption on filters used in high-volume samplers. The year-round average MAC(678) of BC in the rain is almost twice (13.3 +/- 4.2 m(2)/g) compared to the PM10 aerosol (7.2 +/- 2.6 m(2)/g). A possible explanation is the elevated ratio of organic carbon (OC) to BC observed in rain particulate matter (9.4 +/- 6.3) compared to in the aerosols (OC/BC 2.6 +/- 1.4 and water-insoluble organic carbon/BC 1.2 +/- 0.8), indicating a coating-enhancement effect. In addition to BC, we also investigated the MAC(365) of water-soluble brown carbon in PM10 (0.4 +/- 0.4 m(2)/g, at 365 nm). In contrast to BC, MAC(365)brown carbon relates to air mass history, showing higher values for samples from air originating over the South Asian landmass. Furthermore, calculated washout ratios are much lower for BC compared to OC and inorganic ions such as sulfate, implying a longer atmospheric lifetime for BC. The wet deposition flux for BC during the high loading winter was 3 times higher than during the wet summer, despite much less precipitation in the winter.
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| 8. |
- Budhavant, Krishnakant, et al.
(författare)
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Radiocarbon-based source apportionment of elemental carbon aerosols at two South Asian receptor observatories over a full annual cycle
- 2015
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 10:6
-
Tidskriftsartikel (refereegranskat)abstract
- Black carbon (BC) aerosols impact climate and air quality. Since BC from fossil versus biomass combustion have different optical properties and different abilities to penetrate the lungs, it is important to better understand their relative contributions in strongly affected regions such as South Asia. This study reports the first year-round C-14-based source apportionment of elemental carbon (EC), the mass-based correspondent to BC, using as regional receptor sites the international Maldives Climate Observatory in Hanimaadhoo (MCOH) and the mountaintop observatory of the Indian Institute of Tropical Meteorology in Sinhagad, India (SINH). For the highly-polluted winter season (December-March), the fractional contribution to EC from biomass burning (f(bio)) was 53 +/- 5% (n = 6) atMCOHand 56 +/- 3% at SINH (n = 5). The f(bio) for the non-winter remainder was 53 +/- 11% (n = 6) atMCOHand 48 +/- 8%(n = 7) at SINH. This observation-based constraint on near-equal contributions from biomass burning and fossil fuel combustion at both sites compare with predictions from eight technology-based emission inventory (EI) models for India of (f(bio)) EI spanning 55-88%, suggesting that most current EI for Indian BC systematically under predict the relative contribution of fossil fuel combustion. Acontinued iterative testing of bottom-up EI with top-down observational source constraints has the potential to lead to reduced uncertainties regarding EC sources and emissions to the benefit of both models of climate and air quality as well as guide efficient policies to mitigate emissions.
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| 9. |
- Chandrika Ranjendra Nair, Hari Ram, 1989-, et al.
(författare)
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Aerosol demasking enhances climate warming over South Asia
- 2023
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Ingår i: npj Climate and Atmospheric Science. - 2397-3722. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Anthropogenic aerosols mask the climate warming caused by greenhouse gases (GHGs). In the absence of observational constraints, large uncertainties plague the estimates of this masking effect. Here we used the abrupt reduction in anthropogenic emissions observed during the COVID-19 societal slow-down to characterize the aerosol masking effect over South Asia. During this period, the aerosol loading decreased substantially and our observations reveal that the magnitude of this aerosol demasking corresponds to nearly three-fourths of the CO2-induced radiative forcing over South Asia. Concurrent measurements over the northern Indian Ocean unveiled a ~7% increase in the earth’s surface-reaching solar radiation (surface brightening). Aerosol-induced atmospheric solar heating decreased by ~0.4 K d−1. Our results reveal that under clear sky conditions, anthropogenic emissions over South Asia lead to nearly 1.4 W m−2 heating at the top of the atmosphere during the period March–May. A complete phase-out of today’s fossil fuel combustion to zero-emission renewables would result in rapid aerosol demasking, while the GHGs linger on.
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| 10. |
- Chandrika Ranjendra Nair, Hari Ram, 1989-, et al.
(författare)
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Aerosol demasking enhances climate warming over South Asia
- 2023
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Ingår i: npj Climate and Atmospheric Science. - 2397-3722. ; 6:1
-
Tidskriftsartikel (refereegranskat)abstract
- Anthropogenic aerosols mask the climate warming caused by greenhouse gases (GHGs). In the absence of observational constraints, large uncertainties plague the estimates of this masking effect. Here we used the abrupt reduction in anthropogenic emissions observed during the COVID-19 societal slow-down to characterize the aerosol masking effect over South Asia. During this period, the aerosol loading decreased substantially and our observations reveal that the magnitude of this aerosol demasking corresponds to nearly three-fourths of the CO2-induced radiative forcing over South Asia. Concurrent measurements over the northern Indian Ocean unveiled a ~7% increase in the earth’s surface-reaching solar radiation (surface brightening). Aerosol-induced atmospheric solar heating decreased by ~0.4 K d−1. Our results reveal that under clear sky conditions, anthropogenic emissions over South Asia lead to nearly 1.4 W m−2 heating at the top of the atmosphere during the period March–May. A complete phase-out of today’s fossil fuel combustion to zero-emission renewables would result in rapid aerosol demasking, while the GHGs linger on.
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| 11. |
- Dasari, Sanjeev, et al.
(författare)
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Observation-constrained atmospheric lifetime and emission fluxes of black carbon aerosols over South Asia
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Black carbon (BC) aerosols cause climate perturbation and affect air quality/human health. In densely populated South Asia—where the warming effect of BC is estimated to be ~ orders of magnitude higher than the global average—model simulations underestimate the wintertime atmospheric abundance of BC relative to surface observations. Two possible explanations for this model-observation offset are ill-constrained regional emission fluxes and atmospheric BC lifetime (τBC). Here, we combine hourly-resolved BC and carbon monoxide (CO) measurements for three successive winters from a South Asian receptor site—the Maldives Climate Observatory at Hanimaadhoo (MCOH)—in inverse frameworks, to assess the impact of emissions fluxes and lifetimes on ambient BC concentrations. The average ΔBC/ΔCO ratio (background corrected) at MCOH of 14±5 ng m-3 ppb-1 is found to be 2-3 times higher than in the East Asian outflow (range: 2 to 8 ng m-3 ppb-1). A BC transport efficiency of ~86% suggests low influence of wet scavenging processes during the dry South Asian winter period. Using statistical time series analysis, the τBC for dry wintertime South Asia is estimated to be 8±0.5 days, which is higher than commonly used in models. By coupling air mass back trajectories, lifetimes, and the ΔBC/ΔCO time-series data within an inverse modelling framework, we provide an observation-based “top-down” BC emission flux for South Asia estimated to be ~2.4±1 Tg/year. This is significantly higher than estimates from current “bottom-up” emission inventories (EIs). Taken together, this study suggests that to reconcile long-standing BC model-observation offsets in South Asia, existing emission estimates may need to be more than doubled in magnitude.
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| 12. |
- Dasari, Sanjeev, 1989-, et al.
(författare)
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Observational Evidence of Large Contribution from Primary Sources for Carbon Monoxide in the South Asian Outflow
- 2022
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 56:1, s. 165-174
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Tidskriftsartikel (refereegranskat)abstract
- South Asian air is among the most polluted in the world, causing premature death of millions and asserting a strong perturbation of the regional climate. A central component is carbon monoxide (CO), which is a key modulator of the oxidizing capacity of the atmosphere and a potent indirect greenhouse gas. While CO concentrations are declining elsewhere, South Asia exhibits an increasing trend for unresolved reasons. In this paper, we use dual-isotope (δ13C and δ18O) fingerprinting of CO intercepted in the South Asian outflow to constrain the relative contributions from primary and secondary CO sources. Results show that combustion-derived primary sources dominate the wintertime continental CO fingerprint (fprimary ∼ 79 ± 4%), significantly higher than the global estimate (fprimary ∼ 55 ± 5%). Satellite-based inventory estimates match isotope-constrained fprimary-CO, suggesting observational convergence in source characterization and a prospect for model–observation reconciliation. This “ground-truthing” emphasizes the pressing need to mitigate incomplete combustion activities for climate/air quality benefits in South Asia.
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| 13. |
- Dasari, Sanjeev, et al.
(författare)
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Photochemical degradation affects the light absorption of water-soluble brown carbon in the South Asian outflow
- 2019
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 5:1
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Tidskriftsartikel (refereegranskat)abstract
- Light-absorbing organic aerosols, known as brown carbon (BrC), counteract the overall cooling effect of aerosols on Earth's climate. The spatial and temporal dynamics of their light-absorbing properties are poorly constrained and unaccounted for in climate models, because of limited ambient observations. We combine carbon isotope forensics (delta C-13) with measurements of light absorption in a conceptual aging model to constrain the loss of light absorptivity (i.e., bleaching) of water-soluble BrC (WS-BrC) aerosols in one of the world's largest BrC emission regions-South Asia. On this regional scale, we find that atmospheric photochemical oxidation reduces the light absorption of WS-BrC by similar to 84% during transport over 6000 km in the Indo-Gangetic Plain, with an ambient first-order bleaching rate of 0.20 +/- 0.05 day(-1) during over-ocean transit across Bay of Bengal to an Indian Ocean receptor site. This study facilitates dynamic parameterization of WS-BrC absorption properties, thereby constraining BrC climate impact over South Asia.
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| 14. |
- Dasari, Sanjeev, et al.
(författare)
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Source Quantification of South Asian Black Carbon Aerosols with Isotopes and Modeling
- 2020
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 54:19, s. 11771-11779
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Tidskriftsartikel (refereegranskat)abstract
- Black carbon (BC) aerosols perturb climate and impoverish air quality/ human health-affecting similar to 1.5 billion people in South Asia. However, the lack of source-diagnostic observations of BC is hindering the evaluation of uncertain bottom-up emission inventories (EIs) and thereby also models/policies. Here, we present dual-isotope-based (Delta C-14/delta C-13) fingerprinting of wintertime BC at two receptor sites of the continental outflow. Our results show a remarkable similarity in contributions of biomass and fossil combustion, both from the site capturing the highly populated highly polluted Indo-Gangetic Plain footprint (IGP; Delta C-14-f(biomass) = 50 +/- 3%) and the second site in the N. Indian Ocean representing a wider South Asian footprint (52 +/- 6%). Yet, both sites reflect distinct delta C-13-fingerprints, indicating a distinguishable contribution of C-4-biomass burning from peninsular India (PI). Tailored-model-predicted seasonaveraged BC concentrations (700 +/- 440 ng m(-3)) match observations (740 +/- 250 ng m(-3)), however, unveiling a systematically increasing model-observation bias (+19% to -53%) through winter. Inclusion of BC from open burning alone does not reconcile predictions (f(biomass) = 44 +/- 8%) with observations. Direct source-segregated comparison reveals regional offsets in anthropogenic emission fluxes in EIs, overestimated fossil-BC in the IGP, and underestimated biomass-BC in PI, which contributes to the model-observation bias. This ground-truthing pinpoints uncertainties in BC emission sources, which benefit both climate/air-quality modeling and mitigation policies in South Asia.
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| 15. |
- Gawhane, R. D., et al.
(författare)
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Anthropogenic fine aerosols dominate over the Pune region, Southwest India
- 2019
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Ingår i: Meteorology and atmospheric physics (Print). - : Springer Science and Business Media LLC. - 0177-7971 .- 1436-5065. ; 131:5, s. 1497-1508
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Tidskriftsartikel (refereegranskat)abstract
- The major water-soluble ions, organic carbon (OC), elemental carbon (EC) and mass concentration of fine- (PM2.5) and coarse-mode (PM10-2.5) aerosols were measured at Pune during January-December 2016. The mass closure approach was used by comparing the sum of the masses of the individual chemical species to the gravimetric PM obtained by weighting the filter samples. The 1 year mean total mass concentration of fine and coarse mode was 40 mu gm(-3) (64%) and 23 mu g m(-3) (36%), respectively. The PM2.5/PM10 ratio was 0.64 +/- 0.9 indicating an abundance of fine-mode particles over Pune during the study period. A principal component analysis identified three components, where the one with highest explanatory power (59%) displayed clear impact of anthropogenic sources on the measured mass concentration of a majority of the compounds. The strong linear relationships between EC, OC, nss-SO42- and nss-K+ suggest a predominance of a common primary source, with a contribution from biofuel as well as biomass burning sources. Keeping the strong correlation and sources of individual chemical species as the base, it was noticed that (1) major contributors to fine- and coarse-mode particles over the Pune regions are carbonaceous aerosols and secondary inorganic aerosols (non-sea-salt SO42-, NO3-, and NH4+), (2) anthropogenic aerosols contribute mostly to the fine-mode, and (3) meteorological parameters play an important role in controlling levels of fine- and coarse-mode particles. Taken together, the study clearly indicates the dominance of anthropogenic sources during the entire year with more significance in the winter season.
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| 16. |
- Kesti, Jutta, et al.
(författare)
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Changes in aerosol size distributions over the Indian Ocean during different meteorological conditions
- 2020
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Ingår i: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 72:1
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Tidskriftsartikel (refereegranskat)abstract
- Aerosol emissions in South Asia are large. The emitted aerosols can travel significant distances and, during the Asian southwest monsoon especially, are prone to modification through cloud processing and wet scavenging while being transported. The scale of emissions and transport means that the global climate impact of these aerosols are sensitive to modification en route, but the process-level understanding is still largely lacking. In this study, we analyse long-term aerosol data measured at an observatory established in Hanimaadhoo, Republic of Maldives, to investigate the long-term properties of aerosols over the Indian Ocean as well as to understand the effect of precipitation on the aerosol particle size distribution during long-range transport. The observatory location is ideal because it is a receptor site with little local influence, and, depending on the season, receives either polluted air masses coming from the Indian subcontinent or clean marine air masses from the Indian Ocean. We analysed the sub-micron particle number size distribution measured during the years 2004-2008, and 2014-2017, and this is the first inter-seasonal long-term study of the sub-micron aerosol features in the region. The aerosol origin and its relative exposure to wet scavenging during long-range transport were analysed using back-trajectory analysis from HYSPLIT. By comparing aerosol measurements to precipitation along its transport, this study shows that there is a substantial change in particle number size distributions and concentrations depending on the amount of rainfall during transport. During the southwest monsoon season, the aerosol size distribution was notably bimodal and total particle concentrations clearly reduced in comparison with the prevailing aerosol size distribution during the northeast monsoon season. Precipitation during transport usually corresponded with a greater reduction in accumulation mode concentrations than for smaller sizes, and the shape of the median size distribution showed a clear dependence on the trajectory origin and route taken.
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| 17. |
- Kirillova, Elena N., et al.
(författare)
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C-13- and C-14-based study of sources and atmospheric processing of water-soluble organic carbon (WSOC) in South Asian aerosols
- 2013
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Ingår i: Journal of Geophysical Research - Atmospheres. - : American Geophysical Union (AGU). - 2169-897X .- 2169-8996. ; 118:2, s. 614-626
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Tidskriftsartikel (refereegranskat)abstract
- Water-soluble organic carbon (WSOC) is typically a large component of carbonaceous aerosols with a high propensity for inducing cloud formation. The sources of WSOC, which may be both of primary and secondary origins, are in general poorly constrained. This study assesses the concentrations and dual-carbon isotope (14C and 13C) signatures of South Asian WSOC during a 15-month continuous campaign in 2008-2009. Total suspended particulate matter samples were collected at Sinhagad (SINH) India and at the Maldives Climate Observatory at Hanimaadhoo (MCOH). Monsoon-driven meteorology yields significant WSOC concentration differences between the dry winter season (0.94±0.43 μg m-3 MCOH and 3.6±2.3 μg m-3 SINH) and the summer monsoon season (0.10±0.04 μg m-3 MCOH and 0.35±0.21 μg m-3 SINH). Radiocarbon-based source apportionment of WSOC shows the dominance of biogenic/biomass combustion sources but also a substantial anthropogenic fossil-fuel contribution (17±4% MCOH and 23±4% SINH). Aerosols reaching MCOH after long-range over-ocean transport were enriched by 3-4‰ in δ13C-WSOC relative to SINH. This is consistent with particle-phase aging processes influencing the δ13C-WSOC signal in the South Asian regional receptor atmosphere.
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| 18. |
- Nair, H.R.C.R., et al.
(författare)
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Roles of water-soluble aerosol coatings for the enhanced radiative absorption of black carbon over south asia and the northern indian ocean
- 2024
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Ingår i: Science of the Total Environment. - 0048-9697 .- 1879-1026. ; 926, s. 171721-171721
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Tidskriftsartikel (refereegranskat)abstract
- Black Carbon (BC), formed by incomplete combustion, absorbs solar radiation and heats the atmosphere. We investigated the enhancement in optical absorption of BC due to coatings of water-soluble (WS) species in the polluted South Asian atmosphere. The BC Mass Absorption Cross-section (MAC; 678 nm) was estimated before and after removal of the WS components. Wintertime samples were collected from three South Asian receptor observatories intercepting large-footprint outflow: Bangladesh Climate Observatory Bhola (BCOB; integrating outflow of the Indo-Gangetic Plain), Maldives Climate Observatories at Hanimaadhoo (MCOH) and at Gan (MCOG), both reflecting outflow from the South Asian region. The ambient MAC observed at BCOB, MCOH and MCOG were 4.2 ± 1.4, 7.9 ± 1.9 and 7.1 ± 1.5 m2 g−1, respectively.The average enhancement of the BC MAC due to WS coatings (i.e., ws-EMAC) was identical at all three sites (1.6 ± 0.5) indicating that the anthropogenic aerosols had already evolved to a fully coated morphology at BCOB and/or that subsequent aging involved two compensating evolution processes of the coating. Inspecting the key coating component sulfate; the sulfate-to-BC ratio increased threefold when transitioning from BCOB to MCOH and by about 1.5 times from BCOB to MCOG. Conversely, both WS organic carbon (WSOC)/BC and water-insoluble OC (WIOC)/BC ratios declined with distance: WSOC/BC diminished by 84 % from BCOB to MCOH and by 80 % from BCOB to MCOG, while WIOC/BC dropped by about 63 % and 59 %, respectively. Such declines in WSOC and WIOC reflect a combination of photochemical oxidation and more efficient washout of OC compared to BC. The observed changes in the SO42−/BC and WSOC/BC ratios across South Asia highlight the significant impact of aerosol composition on the optical properties of Black Carbon (BC). These findings emphasize the need for detailed studies on aerosol composition to improve climate models and develop effective strategies for reducing the impact of anthropogenic aerosols on the climate.
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| 19. |
- Nair, H. R. C. R., et al.
(författare)
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Source apportionment of black carbon using radiocarbon and stable carbon isotopes during COVID-19 societal slowdown in South Asia
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Black carbon (BC) aerosol emissions in South Asia perturb the regional climate system and significantly degrade the air quality, affecting the health and environment of approximately 1.5 billion people. This study investigates the alterations in BC sources during the societal slowdown during the 2020 COVID-19 pandemic, capitalizing on aerosol samples of the intercepted South Asian outflow at receptor stations of the Maldives Climate Observatory at Hanimaadhoo (MCOH) and the Bangladesh Climate Observatory at Bhola (BCOB). The study used dual-carbon isotopes (Δ14C and δ13C) to understand the impact of societal disruptions on BC levels and sources. The isotope source fingerprinting of BC in the outflow from the Indo-Gangetic Plain (at BCOB) revealed that for the COVID period, a decreasing contribution from fossil fuel (from 49% down to 35%) amidst an increase in the fraction from C3 biomass burning going from 31% to 55% with C4 biomass burning remaining as a minor contributor. Similarly, for MCOH, reflecting the outflow from the greater S Asian subcontinent, the contribution from fossil combustion decreased while C3 combustion correspondingly increased. This likely reflects both decreased transport and an increase in crop residue burning and the use of biomass for heating and cooking. These dual-isotope constraints demonstrate that a decisive shift in emissions of climate-forcing BC aerosols occurred during the pandemic slowdown, suggesting that a societal transformation away from fossil fuel reliance will quickly propagate into the aerosol composition over South Asia.
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| 20. |
- Papazian, Stefano, 1986-, et al.
(författare)
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Nontarget mass spectrometry and in silico molecular characterization of air pollution from the Indian subcontinent
- 2022
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Ingår i: Communications Earth & Environment. - : Springer Science and Business Media LLC. - 2662-4435. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- A combination of high-resolution mass spectrometry and computational molecular characterization techniques can structurally annotate up to 17% of organic compounds in fine particulate matter in highly polluted air sampled in the Maldives. Fine particulate-matter is an important component of air pollution that impacts health and climate, and which delivers anthropogenic contaminants to remote global regions. The complex composition of organic molecules in atmospheric particulates is poorly constrained, but has important implications for understanding pollutant sources, climate-aerosol interactions, and health risks of air pollution exposure. Here, comprehensive nontarget high-resolution mass spectrometry was combined with in silico structural prediction to achieve greater molecular-level insight for fine particulate samples (n = 40) collected at a remote receptor site in the Maldives during January to April 2018. Spectral database matching identified 0.5% of 60,030 molecular features observed, while a conservative computational workflow enabled structural annotation of 17% of organic structures among the remaining molecular dark matter. Compared to clean air from the southern Indian Ocean, molecular structures from highly-polluted regions were dominated by organic nitrogen compounds, many with computed physicochemical properties of high toxicological and climate relevance. We conclude that combining nontarget analysis with computational mass spectrometry can advance molecular-level understanding of the sources and impacts of polluted air.
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| 21. |
- Sheesley, Rebecca J., et al.
(författare)
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Year round radiocarbon based source apportionment of carbonaceous aerosols at two background sites in south asia
- 2012
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117, s. D10202-
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric Brown Clouds (ABC), regional-scale haze events, are a significant concern for both human cardiopulmonary health and regional climate impacts. In order to effectively mitigate this pollution-based phenomenon, it is imperative to understand the magnitude, scope and source of ABC in regions such as South Asia. Two sites in S. Asia were chosen for a 15-month field campaign focused on isotope-based source apportionment of carbonaceous aerosols in 2008-2009. Both the Maldives Climate Observatory in Hanimaadhoo (MCOH) and a mountaintop site in Sinhagad, India (SINH) act as regionally mixed receptor sites. Annual radiocarbon-based source apportionment for soot elemental carbon (SEC) at MCOH and SINH revealed 73 +/- 6% and 59 +/- 5% contribution from biomass combustion, respectively (remainder from fossil fuel). The contributions from biogenic/biomass combustion to total organic carbon were similar between MCOH and SINH (69 +/- 5% and 64 +/- 5, respectively). The biomass combustion contribution for SEC in the current study, especially the results from MCOH, shows good agreement with published black carbon emissions inventories for India. Geographic source assessment, including clustered back trajectory analysis and carbon contribution by source region, indicated that the highest SEC/TOC loads originated from the W. Indian coastal margin, including the coastal city of Mumbai, India. The winter dry season C-14-based source apportionment of the BC-tracing SEC fraction for 2006, 2008, 2009 were not statistically different (p = 0.7) and point to a near-constant two-thirds contribution from biomass combustion practices, including wood and other biofuels as well as burning of agricultural crop residues.
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| 22. |
- Varpe, Sandeep R., et al.
(författare)
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Heterogeneity in aerosol characteristics at the semi-arid and island AERONET observing sites in India and Maldives
- 2018
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Ingår i: International Journal of Remote Sensing. - : Informa UK Limited. - 0143-1161 .- 1366-5901. ; 39:19, s. 6137-6169
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Tidskriftsartikel (refereegranskat)abstract
- Multi-year Aerosol Robotic Network (AERONET) direct Sun retrieved and inversion algorithm derived aerosol products at a semi-arid, urban site, Jaipur (26.90 degrees N, 75.80 degrees E) and island observing site, Maldives Climate Observatory-Hanimaadhoo (MCO-Hanimaadhoo, 6.74 degrees N, 73.17 degrees E) are analysed to investigate heterogeneity in aerosol optical and microphysical properties. Results reveal the existence of a large seasonal diversity in the frequency distributions of aerosol optical depth (AOD(500) (nm), AOD(1020) (nm)) and angstrom ngstrom exponent (AE(440-870) (nm)) during different seasons at Jaipur and MCO-Hanimaadhoo. These are indicative of the advection of different aerosol types (viz., black carbon (BC) aerosol, organic aerosol, sulfate particle, dust, sea salt, nitrate particle, and mixtures thereof) from a variety of production mechanisms influenced by strong seasonal changes of anthropogenic activities as well as modulations induced by the climatic condition. The cumulative frequency analysis of the single scattering albedo (SSA) difference (i.e. Delta SSA = SSA(440) (nm) - SSA(1020) (nm)) shows that at Jaipur Delta SSA is predominantly negative (around 88% days) while at MCO-Hanimaadhoo it is positive (around 74% days). The positive and negative values of Delta SSA are respectively linked to a stronger absorption by BC mixed anthropogenic pollution aerosols at 1020 nm and to a stronger absorption by mineral dust containing iron oxide at 440 nm. The spectral behaviour of SSA, thus, facilitates investigation of the existence of iron oxide or BC in aerosols. The 'Bivariate Kernel density' plots of SSA versus fine-mode fraction (FMF) of AOD(440) (nm)/AE(440-870) (nm) reveal that at Jaipur the aerosol ensemble consists of coarse-mode particles (AE and FMF cluster in the range 0.2-0.4), a dominant category along with significant fine-mode and much less mixed category. At MCO-Hanimaadhoo fine-mode particle category (with FMF and AE cluster in the range 0.90-0.95 and 1.2-1.6 respectively) is the only dominant category. The persisting log-normal bimodal feature in aerosol volume size distribution (AVSD) is observed both at Jaipur and MCO-Hanimaadhoo. The modal volume concentration of coarse-mode aerosol decreases from FMF of AOD(675) (nm) = 0.25 (inherently belonging to the coarse-mode regime) to FMF of AOD(675) (nm) = 0.95 (inherently belonging to the fine-mode regime). This transformation in coarse-to fine-mode volume concentration is associated with a steady rise in AE(440-874) (nm) supporting this changeover.
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