Source-Based Size-Resolved Optical Properties of Carbonaceous Aerosols

In this study, the source-based optical properties of polydisperse carbonaceous aerosols were determined from PM2.5 concentrations measured at a Global Atmospheric Watch station in South Korea. The extinction and absorption coefficients of carbonaceous aerosols were calculated using the Mie theory and assuming a lognormal size distribution. Based on the mass concentration from the EPA’s Positive Matrix Factorization (PMF) receptor model, which considers five source identification and apportionment factors (biogenic source, local biomass burning, secondary organic aerosol, transported biomass burning, and mixed sources), the source-based size-resolved mass extinction and absorption efficiencies were estimated for each source using a multilinear regression model. The results show that the source-based optical properties depend on the aerosol size and physicochemical characteristics of the chemical compounds. The long-range transport of biomass burning (LBB) aerosol, which has a mass concentration of 20%, holds a 12.1–23.1% total extinction efficiency—depending on the size and refractive index—in the range of 0.1–0.5 μm in geometric mean diameter and humic-like substances (HULIS) imaginary refractive index of 0.006–0.3. Biogenic sources of aerosols with small diameters have higher mass absorption efficiencies (MAE) than other sources, depending on the size and refractive index.

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Remote sensing of soot carbon – Part 1: Distinguishing different absorbing aerosol species

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-13607-2015 ◽

2015 ◽

Vol 15 (9) ◽

pp. 13607-13656 ◽

Cited By ~ 4

Author(s):

G. L. Schuster ◽

O. Dubovik ◽

A. Arola

Keyword(s):

Refractive Index ◽

Optical Properties ◽

Iron Oxide ◽

South America ◽

Biomass Burning ◽

Southern Africa ◽

Refractive Indices ◽

Carbonaceous Aerosols ◽

Fine Mode ◽

Soot Carbon

Abstract. We describe a method of using the aerosol robotic network (AERONET) size distributions and complex refractive indices to retrieve the relative proportion of carbonaceous aerosols and iron oxide minerals. We assume that soot carbon has a spectrally flat refractive index, and that enhanced imaginary indices at the 440 nm wavelength are caused by brown carbon or hematite. Carbonaceous aerosols can be separated from dust in imaginary refractive index space because 95% of biomass burning aerosols have imaginary indices greater than 0.0042 at the 675–1020 nm wavelengths, and 95% of dust has imaginary refractive indices of less than 0.0042 at those wavelengths. However, mixtures of these two types of particles can not be unambiguously partitioned on the basis of optical properties alone, so we also separate these particles by size. Regional and seasonal results are consistent with expectations. Monthly climatologies of fine mode soot carbon are less than 1.0% by volume for West Africa and the Middle East, but the southern Africa and South America biomass burning sites have peak values of 3.0 and 1.7%. Monthly-averaged fine mode brown carbon volume fractions have a peak value of 5.8% for West Africa, 2.1% for the Middle East, 3.7% for southern Africa, and 5.7% for South America. Monthly climatologies of iron oxide volume fractions show little seasonal variability, and range from about 1.1 to 1.7% for coarse mode aerosols in all four study regions. Finally, our sensitivity study indicates that the soot carbon retrieval is not sensitive to the component refractive indices or densities assumed for carbonaceous and iron oxide aerosols, and differs by only 15.4% when these parameters are altered from our chosen baseline values. The associated soot carbon absorption aerosol optical depth (AAOD) does not vary at all when these parameters are altered, however, because the retrieval is constrained by the AERONET optical properties.

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Insights into the aging of biomass burning aerosol from satellite observations and 3D atmospheric modeling: evolution of the aerosol optical properties in Siberian wildfire plumes

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-357-2021 ◽

2021 ◽

Vol 21 (1) ◽

pp. 357-392

Author(s):

Igor B. Konovalov ◽

Nikolai A. Golovushkin ◽

Matthias Beekmann ◽

Meinrat O. Andreae

Keyword(s):

Optical Properties ◽

Long Range ◽

Biomass Burning ◽

Organic Aerosol ◽

Satellite Observations ◽

Long Range Transport ◽

Aerosol Optical Properties ◽

Smoke Plumes ◽

Range Transport ◽

Aerosol Aging

Abstract. Long-range transport of biomass burning (BB) aerosol from regions affected by wildfires is known to have a significant impact on the radiative balance and air quality in receptor regions. However, the changes that occur in the optical properties of BB aerosol during long-range transport events are insufficiently understood, limiting the adequacy of representations of the aerosol processes in chemistry transport and climate models. Here we introduce a framework to infer and interpret changes in the optical properties of BB aerosol from satellite observations of multiple BB plumes. Our framework includes (1) a procedure for analysis of available satellite retrievals of the absorption and extinction aerosol optical depths (AAOD and AOD) and single-scattering albedo (SSA) as a function of the BB aerosol photochemical age and (2) a representation of the AAOD and AOD evolution with a chemistry transport model (CTM) involving a simplified volatility basis set (VBS) scheme with a few adjustable parameters. We apply this framework to analyze a large-scale outflow of BB smoke plumes from Siberia toward Europe that occurred in July 2016. We use AAOD and SSA data derived from OMI (Ozone Monitoring Instrument) satellite measurements in the near-UV range along with 550 nm AOD and carbon monoxide (CO) columns retrieved from MODIS (Moderate Resolution Imaging Spectroradiometer) and IASI (Infrared Atmospheric Sounding Interferometer) satellite observations, respectively, to infer changes in the optical properties of Siberian BB aerosol due to its atmospheric aging and to get insights into the processes underlying these changes. Using the satellite data in combination with simulated data from the CHIMERE CTM, we evaluate the enhancement ratios (EnRs) that allow isolating AAOD and AOD changes due to oxidation and gas–particle partitioning processes from those due to other processes, including transport, deposition, and wet scavenging. The behavior of EnRs for AAOD and AOD is then characterized using nonlinear trend analysis. It is found that the EnR for AOD strongly increases (by about a factor of 2) during the first 20–30 h of the analyzed evolution period, whereas the EnR for AAOD does not exhibit a statistically significant increase during this period. The increase in AOD is accompanied by a statistically significant enhancement of SSA. Further BB aerosol aging (up to several days) is associated with a strong decrease in EnRs for both AAOD and AOD. Our VBS simulations constrained by the observations are found to be more consistent with satellite observations of strongly aged BB plumes than “tracer” simulations in which atmospheric transformations of BB organic aerosol were disregarded. The simulation results indicate that the upward trends in EnR for AOD and in SSA are mainly due to atmospheric processing of secondary organic aerosol (SOA), leading to an increase in the mass scattering efficiency of BB aerosol. Evaporation and chemical fragmentation of the SOA species, part of which is assumed to be absorptive (to contain brown carbon), are identified as likely reasons for the subsequent decrease in the EnR for both AAOD and AOD. Hence, our analysis reveals that the long-range transport of smoke plumes from Siberian fires is associated with major changes in BB aerosol optical properties and chemical composition. Overall, this study demonstrates the feasibility of using available satellite observations for evaluating and improving representations in atmospheric models of the BB aerosol aging processes in different regions of the world at much larger temporal scales than those typically addressed in aerosol chamber experiments.

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Six-year source apportionment of submicron organic aerosols from near-continuous highly time-resolved measurements at SIRTA (Paris area, France)

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-14755-2019 ◽

2019 ◽

Vol 19 (23) ◽

pp. 14755-14776 ◽

Cited By ~ 8

Author(s):

Yunjiang Zhang ◽

Olivier Favez ◽

Jean-Eudes Petit ◽

Francesco Canonaco ◽

Francois Truong ◽

...

Keyword(s):

Source Apportionment ◽

Biomass Burning ◽

Ambient Air ◽

Carbonaceous Aerosols ◽

Time Resolved ◽

Pronounced Increase ◽

Paris Area ◽

Range Transport ◽

High Concentrations

Abstract. Organic aerosol (OA) particles are recognized as key factors influencing air quality and climate change. However, highly time-resolved long-term characterizations of their composition and sources in ambient air are still very limited due to challenging continuous observations. Here, we present an analysis of long-term variability of submicron OA using the combination of an aerosol chemical speciation monitor (ACSM) and a multiwavelength Aethalometer from November 2011 to March 2018 at a peri-urban background site of the Paris region (France). Source apportionment of OA was achieved via partially constrained positive matrix factorization (PMF) using the multilinear engine (ME-2). Two primary OA (POA) and two oxygenated OA (OOA) factors were identified and quantified over the entire studied period. POA factors were designated as hydrocarbon-like OA (HOA) and biomass burning OA (BBOA). The latter factor presented a significant seasonality with higher concentrations in winter with significant monthly contributions to OA (18 %–33 %) due to enhanced residential wood burning emissions. HOA mainly originated from traffic emissions but was also influenced by biomass burning in cold periods. OOA factors were distinguished between their less- and more-oxidized fractions (LO-OOA and MO-OOA, respectively). These factors presented distinct seasonal patterns, associated with different atmospheric formation pathways. A pronounced increase in LO-OOA concentrations and contributions (50 %–66 %) was observed in summer, which may be mainly explained by secondary OA (SOA) formation processes involving biogenic gaseous precursors. Conversely, high concentrations and OA contributions (32 %–62 %) of MO-OOA during winter and spring seasons were partly associated with anthropogenic emissions and/or long-range transport from northeastern Europe. The contribution of the different OA factors as a function of OA mass loading highlighted the dominant roles of POA during pollution episodes in fall and winter and of SOA for highest springtime and summertime OA concentrations. Finally, long-term trend analyses indicated a decreasing feature (of about −175 ng m−3 yr−1) for MO-OOA, very limited or insignificant decreasing trends for primary anthropogenic carbonaceous aerosols (BBOA and HOA, along with the fossil-fuel and biomass-burning black carbon components) and no statistically significant trend for LO-OOA over the 6-year investigated period.

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Chemical and optical properties of carbonaceous aerosols in Nanjing, eastern China: regionally transported biomass burning contribution

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-11213-2019 ◽

2019 ◽

Vol 19 (17) ◽

pp. 11213-11233 ◽

Cited By ~ 8

Author(s):

Xiaoyan Liu ◽

Yan-Lin Zhang ◽

Yiran Peng ◽

Lulu Xu ◽

Chunmao Zhu ◽

...

Keyword(s):

Optical Properties ◽

Organic Carbon ◽

Solar Energy ◽

Energy Absorption ◽

Biomass Burning ◽

Eastern China ◽

Water Soluble ◽

Carbonaceous Aerosols ◽

Southeastern China ◽

Brown Carbon

Abstract. Biomass burning can significantly impact the chemical and optical properties of carbonaceous aerosols. Here, the biomass burning impacts were studied during wintertime in a megacity of Nanjing, eastern China. The high abundance of biomass burning tracers such as levoglucosan (lev), mannosan (man), galactosan (gal) and non-sea-salt potassium (nss-K+) was found during the studied period with the concentration ranges of 22.4–1476 ng m−3, 2.1–56.2 ng m−3, 1.4–32.2 ng m−3 and 0.2–3.8 µg m−3, respectively. The significant contribution of biomass burning to water-soluble organic carbon (WSOC; 22.3±9.9 %) and organic carbon (OC; 20.9±9.3 %) was observed in this study. Backward air mass origin analysis, potential emission sensitivity of elemental carbon (EC) and MODIS fire spot information indicated that the elevations of the carbonaceous aerosols were due to the transported biomass-burning aerosols from southeastern China. The characteristic mass ratio maps of lev∕man and lev∕nss-K+ suggested that the biomass fuels were mainly crop residuals. Furthermore, the strong correlation (p < 0.01) between biomass burning tracers (such as lev) and light absorption coefficient (babs) for water-soluble brown carbon (BrC) revealed that biomass burning emissions played a significant role in the light-absorption properties of carbonaceous aerosols. The solar energy absorption due to water-soluble brown carbon and EC was estimated by a calculation based on measured light-absorbing parameters and a simulation based on a radiative transfer model (RRTMG_SW). The solar energy absorption of water-soluble BrC in short wavelengths (300–400 nm) was 0.8±0.4 (0.2–2.3) W m−2 (figures in parentheses represent the variation range of each parameter) from the calculation and 1.2±0.5 (0.3–1.9) W m−2 from the RRTMG_SW model. The absorption capacity of water-soluble BrC accounted for about 20 %–30 % of the total absorption of EC aerosols. The solar energy absorption of water-soluble BrC due to biomass burning was estimated as 0.2±0.1 (0.0–0.9) W m−2, considering the biomass burning contribution to carbonaceous aerosols. Potential source contribution function model simulations showed that the solar energy absorption induced by water-soluble BrC and EC aerosols was mostly due to the regionally transported carbonaceous aerosols from source regions such as southeastern China. Our results illustrate the importance of the absorbing water-soluble brown carbon aerosols in trapping additional solar energy in the low-level atmosphere, heating the surface and inhibiting the energy from escaping the atmosphere.

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Effects of physical and chemical nonlinearities on evolution of optical properties of biomass burning aerosol

10.5194/egusphere-egu2020-7118 ◽

2020 ◽

Author(s):

Nikolai Golovushkin ◽

Igor Konovalov ◽

Matthias Beekmann

Keyword(s):

Optical Properties ◽

Biomass Burning ◽

Mass Concentration ◽

Climate Models ◽

Nonlinear Behavior ◽

Basic Research ◽

Chem Phys ◽

Basis Set ◽

Radiation Budget ◽

Physical And Chemical

Aerosol from open biomass burning (BB) is known to strongly impact the Earth radiation budget. Therefore, a good knowledge of its optical properties and their evolution is an important prerequisite for accurate assessments of contributions of various factors to climate change by means of chemistry-transport and climate models. As a major component of typical BB aerosol is organic matter, the atmospheric evolution of BB aerosol can be strongly affected by the physical and chemical processes governing the gas-particle partitioning of organic compounds. Recently, it has been shown [1] that these processes can give rise to strongly nonlinear behavior of mass concentration of organic fraction of BB aerosol during its atmospheric lifetime. It has been also argued that chemical and physical nonlinearities can explain part of the observed diversity of the effects of BB aerosol atmospheric aging. The present study has extended the previous analysis of the nonlinear behavior of BB aerosol, focusing on the evolution of BB aerosol optical properties, such as, specifically, mass absorption and scattering efficiencies (MAE and MSE) in the near-UV and optical wavelength ranges. The evolution of aerosol in BB plumes was simulated with the MDMOA [1] microphysical box model that involves a schematic parameterization of the dilution process and represents the oxidation and gas-particle partitioning processes within the volatility basis set (VBS) framework. The Mie-theory-based simulations of the optical properties of aging BB aerosol were performed with the OPTSIM module [2] coupled with MDMOA. The simulations show that both MAE and MSE can exhibit strong and diverse changes during BB aerosol evolution mostly due to significant changes in the aerosol particle size distribution. Furthermore, similar to the mass concentration, both MAE and MSC of the aged BB aerosol depend in a nonlinear manner on the initial BB aerosol concentration and the initial size of a smoke plume and are sensitive to the choice of a concrete VBS scheme. The results of this study may have important implications for modeling of radiative effects of BB aerosol with chemistry-transport and climate models and for interpretation of remote observations of BB aerosol.The study was supported by the Russian Foundation for Basic Research (grant No. 18-05-00911).References<ol><li>Konovalov, I. B., Beekmann, M., Golovushkin, N. A., and Andreae, M. O.: Nonlinear behavior of organic aerosol in biomass burning plumes: a microphysical model analysis, Atmos. Chem. Phys., 19, 12091&#8211;12119, https://doi.org/10.5194/acp-19-12091-2019, 2019.</li> <li>Stromatas, S., Turquety, S., Menut, L., Chepfer, H., P&#233;r&#233;, J. C., Cesana, G., and Bessagnet, B.: Lidar signal simulation for the evaluation of aerosols in chemistry transport models, Geosci. Model Dev., 5, 1543&#8211;1564, https://doi.org/10.5194/gmd-5-1543-2012, 2012.</li> </ol>

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Physical and optical properties of aged biomass burning aerosol from wildfires in Siberia and the Western USA at the Mt. Bachelor Observatory

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-15185-2016 ◽

2016 ◽

Vol 16 (23) ◽

pp. 15185-15197 ◽

Cited By ~ 33

Author(s):

James R. Laing ◽

Daniel A. Jaffe ◽

Jonathan R. Hee

Keyword(s):

Optical Properties ◽

Pacific Northwest ◽

Biomass Burning ◽

Geometric Mean ◽

Fine Particulate Matter ◽

Single Scattering ◽

Absorption Efficiency ◽

Size Distributions ◽

Scanning Mobility Particle Sizer ◽

Scattering Coefficients

Abstract. The summer of 2015 was an extreme forest fire year in the Pacific Northwest. Our sample site at the Mt. Bachelor Observatory (MBO, 2.7 km a.s.l.) in central Oregon observed biomass burning (BB) events more than 50 % of the time during August. In this paper we characterize the aerosol physical and optical properties of 19 aged BB events during August 2015. Six of the 19 events were influenced by Siberian fires originating near Lake Baikal that were transported to MBO over 4–10 days. The remainder of the events resulted from wildfires in Northern California and Southwestern Oregon with transport times to MBO ranging from 3 to 35 h. Fine particulate matter (PM1), carbon monoxide (CO), aerosol light scattering coefficients (σscat), aerosol light absorption coefficients (σabs), and aerosol number size distributions were measured throughout the campaign. We found that the Siberian events had a significantly higher Δσabs∕ΔCO enhancement ratio, higher mass absorption efficiency (MAE; Δσabs∕ΔPM1), lower single scattering albedo (ω), and lower absorption Ångström exponent (AAE) when compared with the regional events. We suggest that the observed Siberian events represent that portion of the plume that has hotter flaming fire conditions and thus enabled strong pyroconvective lofting and long-range transport to MBO. The Siberian events observed at MBO therefore represent a selected portion of the original plume that would then have preferentially higher black carbon emissions and thus an enhancement in absorption. The lower AAE values in the Siberian events compared to regional events indicate a lack of brown carbon (BrC) production by the Siberian fires or a loss of BrC during transport. We found that mass scattering efficiencies (MSE) for the BB events ranged from 2.50 to 4.76 m2 g−1. We measured aerosol size distributions with a scanning mobility particle sizer (SMPS). Number size distributions ranged from unimodal to bimodal and had geometric mean diameters (Dpm) ranging from 138 to 229 nm and geometric standard deviations (σg) ranging from 1.53 to 1.89. We found MSEs for BB events to be positively correlated with the geometric mean of the aerosol size distributions (R2 = 0.73), which agrees with Mie theory. We did not find any dependence on event size distribution to transport time or fire source location.

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Optical source apportionment and radiative effect of light-absorbing carbonaceous aerosols in a tropical marine monsoon climate zone: the importance of ship emissions

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-15537-2020 ◽

2020 ◽

Vol 20 (24) ◽

pp. 15537-15549

Author(s):

Qiyuan Wang ◽

Huikun Liu ◽

Ping Wang ◽

Wenting Dai ◽

Ting Zhang ◽

...

Keyword(s):

Optical Properties ◽

Biomass Burning ◽

Motor Vehicle ◽

Motor Vehicles ◽

Carbonaceous Aerosols ◽

Radiative Effect ◽

Monsoon Climate ◽

Ship Emissions ◽

Optical Source ◽

Climate Zone

Abstract. Source-specific optical properties of light-absorbing carbonaceous (LAC) aerosols in the atmosphere are poorly understood because they are generated by various sources. In this study, a receptor model combining multi-wavelength absorption and chemical species was used to explore the source-specific optical properties of LAC aerosols in a tropical marine monsoon climate zone. The results showed that biomass burning and ship emissions were the dominant contributors to average aerosol light absorption. The source-specific absorption Ångström exponent (AAE) indicated that black carbon (BC) was the dominant LAC aerosol in ship and motor vehicle emissions. Moreover, brown carbon (BrC) was present in biomass-burning emissions. The source-specific mass absorption cross section (MAC) showed that BC from ship emissions had a stronger light-absorbing capacity compared to emissions from biomass burning and motor vehicles. The BrC MAC derived from biomass burning was also smaller than the BC MAC and was highly dependent on wavelength. Furthermore, radiative effect assessment indicated a comparable atmospheric forcing and heating capacity of LAC aerosols between biomass burning and ship emissions. This study provides insights into the optical properties of LAC aerosols from various sources. It also sheds more light on the radiative effects of LAC aerosols generated by ship emissions.

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Remote sensing of soot carbon – Part 1: Distinguishing different absorbing aerosol species

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-1565-2016 ◽

2016 ◽

Vol 16 (3) ◽

pp. 1565-1585 ◽

Cited By ~ 43

Author(s):

G. L. Schuster ◽

O. Dubovik ◽

A. Arola

Keyword(s):

Refractive Index ◽

Middle East ◽

West Africa ◽

Biomass Burning ◽

Refractive Indices ◽

Carbonaceous Aerosols ◽

Brown Carbon ◽

Free Iron ◽

Fine Mode ◽

Soot Carbon

Abstract. We describe a method of using the Aerosol Robotic Network (AERONET) size distributions and complex refractive indices to retrieve the relative proportion of carbonaceous aerosols and free iron minerals (hematite and goethite). We assume that soot carbon has a spectrally flat refractive index and enhanced imaginary indices at the 440 nm wavelength are caused by brown carbon or hematite. Carbonaceous aerosols can be separated from dust in imaginary refractive index space because 95 % of biomass burning aerosols have imaginary indices greater than 0.0042 at the 675–1020 nm wavelengths, and 95 % of dust has imaginary refractive indices of less than 0.0042 at those wavelengths. However, mixtures of these two types of particles can not be unambiguously partitioned on the basis of optical properties alone, so we also separate these particles by size. Regional and seasonal results are consistent with expectations. Monthly climatologies of fine mode soot carbon are less than 1.0 % by volume for West Africa and the Middle East, but the southern African and South American biomass burning sites have peak values of 3.0 and 1.7 %. Monthly averaged fine mode brown carbon volume fractions have a peak value of 5.8 % for West Africa, 2.1 % for the Middle East, 3.7 % for southern Africa, and 5.7 % for South America. Monthly climatologies of free iron volume fractions show little seasonal variability, and range from about 1.1 to 1.7 % for coarse mode aerosols in all four study regions. Finally, our sensitivity study indicates that the soot carbon retrieval is not sensitive to the component refractive indices or densities assumed for carbonaceous and free iron aerosols, and the retrieval differs by only 15.4 % when these parameters are altered from our chosen baseline values. The total uncertainty of retrieving soot carbon mass is ∼ 50 % (when uncertainty in the AERONET product and mixing state is included in the analysis).

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Physical and Optical Properties of Aged Biomass Burning Aerosol from Wildfires in Siberia and the Western US at the Mt. Bachelor Observatory

10.5194/acp-2016-518 ◽

2016 ◽

Cited By ~ 1

Author(s):

James R. Laing ◽

Dan A. Jaffe ◽

Jonathan R. Hee

Keyword(s):

Optical Properties ◽

Biomass Burning ◽

Geometric Mean ◽

Fine Particulate Matter ◽

Absorption Efficiency ◽

Absorption Enhancement ◽

Size Distributions ◽

Fire Plume ◽

Scanning Mobility Particle Sizer ◽

North West

Abstract. The summer of 2015 was an extreme forest fire year in the Pacific North West. Our sample site at Mt. Bachelor Observatory (MBO, 2.7 km a.s.l.) in central Oregon observed biomass burning events more than 50 % of the time during August. In this paper we characterize the aerosol physical and optical properties of 19 aged biomass burning (BB) events during August 2015. Six of the nineteen events were influenced by Siberian fires originating near Lake Baikal. The remainder of the events resulted from wildfires in Northern California and Southwestern Oregon with transport times to MBO ranging from 4.5–35 hours. Fine particulate matter (PM1), carbon monoxide (CO), aerosol light scattering (σscat) and absorption (σabs), and aerosol number size distributions were measured throughout the campaign. We found that the Siberian events had significantly higher Δσabs/ΔCO enhancement ratio, higher mass absorption efficiency (MAE; Δσabs/ΔPM1), lower single scattering albedo (ω), and lower Absorption Ångström exponent (AAE) when compared with the regional events. We suspect the Siberian events observed represent a portion of the fire plume that has hotter flaming fire conditions that enabled strong pyro-convective lofting and long transport to MBO. These plumes would then have preferentially higher black carbon emissions and thus absorption enhancement. The lower AAE values in the Siberian events compared to regional events indicates a lack of brown carbon (BrC) production by the Siberian fires or a loss of BrC during transport. We found that mass scattering efficiencies (MSE) for the BB events to range from 2.50–4.76 m2 g−1. We measured aerosol size distributions with a scanning mobility particle sizer (SMPS). Number size distributions ranged from unimodal to bimodal and had geometric mean diameters ranging from 138–229 nm and geometric standard deviations ranging from 1.53–1.89. We found MSE’s for BB events to be positively correlated with the geometric mean of the aerosol size distributions (R2 = 0.73), which agrees with Mie Theory. We did not find any dependence on event size distribution to transport time or fire source location.

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