scholarly journals Heterogeneous OH oxidation of secondary brown carbon aerosol

2018 ◽  
Vol 18 (19) ◽  
pp. 14539-14553 ◽  
Author(s):  
Elijah G. Schnitzler ◽  
Jonathan P. D. Abbatt
Keyword(s):  
Optical Properties ◽  
Single Scattering ◽  
Trace Gas ◽  
Absorption Enhancement ◽  
Brown Carbon ◽  
Scattering Coefficients ◽  
Aerosol Absorption ◽  
Photoacoustic Spectrometer ◽  
In Series ◽  
First Time

Abstract. Light-absorbing organic aerosol, or brown carbon (BrC), has significant but poorly constrained effects on climate; for example, oxidation in the atmosphere may alter its optical properties, leading to absorption enhancement or bleaching. Here, we investigate for the first time the effects of heterogeneous OH oxidation on the optical properties of a laboratory surrogate of aqueous, secondary BrC in a series of photo-oxidation chamber experiments. The BrC surrogate was generated from aqueous resorcinol, or 1,3-dihydroxybenzene, and H2O2 exposed to >300 nm radiation that is atomized, passed through trace gas denuders, and injected into the chamber, which was conditioned to either 15 % or 60 % relative humidity (RH). Aerosol absorption and scattering coefficients and single scattering albedo (SSA) at 405 nm were measured using a photoacoustic spectrometer. At 60 % RH, upon OH exposure, absorption first increased, and the SSA decreased sharply. Subsequently, absorption decreased faster than scattering, and SSA increased gradually. Comparisons to the modelled trend in SSA, based on Mie theory calculations, confirm that the observed trend is due to chemical evolution, rather than slight changes in particle size. The initial absorption enhancement is likely due to molecular functionalization and/or oligomerization and the bleaching to fragmentation. By contrast, at 15 % RH, slow absorption enhancement was observed without appreciable bleaching. A multi-layer kinetics model, consisting of two surface reactions in series, was constructed to provide further insights regarding the RH dependence of the optical evolution. Candidate parameters suggest that the oxidation is efficient, with uptake coefficients on the order of unity. The parameters also suggest that, as RH decreases, reactivity decreases and aerosol viscosity increases, such that particles are well-mixed at 60 % RH but not at 15 % RH. These results further the current understanding of the complex processing of BrC that may occur in the atmosphere.

scholarly journals Heterogeneous OH oxidation of secondary brown carbon aerosol

2018 ◽  
Author(s):  
Elijah G. Schnitzler ◽  
Jonathan P. D. Abbatt
Keyword(s):  
Optical Properties ◽  
Single Scattering ◽  
Trace Gas ◽  
Absorption Enhancement ◽  
Brown Carbon ◽  
Scattering Coefficients ◽  
Aerosol Absorption ◽  
In Series ◽  
First Time ◽  
Slow Absorption

Abstract. Light-absorbing organic aerosol, or brown carbon (BrC), has significant but poorly-constrained effects on climate; for example, oxidation in the atmosphere may alter its optical properties, leading to absorption enhancement or bleaching. Here, we investigate for the first time the effects of heterogeneous OH oxidation on the optical properties of a laboratory surrogate of secondary BrC in a series of photo-oxidation chamber experiments. The BrC surrogate was generated from aqueous resorcinol, or 1,3-dihydroxybenzene, and H2O2 exposed to > 300 nm radiation, atomized, passed through trace gas denuders, and injected into the chamber, which was conditioned to either 15 or 60 % relative humidity (RH). Aerosol absorption and scattering coefficients and single scattering albedo (SSA) at 405 nm were measured using a photo-acoustic spectrometer. At 60 % RH, upon OH exposure, absorption first increased, and the SSA decreased sharply. Subsequently, absorption decreased faster than scattering, and SSA increased gradually. Comparisons to the modelled trend in SSA, based on Mie theory calculations, confirm that the observed trend is due to chemical evolution, rather than slight changes in particle size. The initial absorption enhancement is likely due to molecular functionalization and/or oligomerization, and the bleaching to fragmentation. By contrast, at 15 % RH, slow absorption enhancement was observed, without appreciable bleaching. A multi-layer kinetics model, consisting of two surface reactions in series, was constructed to provide further insights regarding the RH-dependence of the optical evolution. Candidate parameters suggest that the oxidation is efficient, with uptake coefficients on the order of unity, and the aerosol is very viscous, even at 60 % RH. At 15 % RH, the aerosol will be viscous enough to confine products of fragmentation, leading to their recombination, such that little bleaching is observed on the experimental timescale. These results further the current understanding of the complex processing of BrC that may occur in the atmosphere.

scholarly journals South African EUCAARI measurements: seasonal variation of trace gases and aerosol optical properties

2012 ◽  
Vol 12 (4) ◽  
pp. 1847-1864 ◽  
Author(s):  
L. Laakso ◽  
V. Vakkari ◽  
A. Virkkula ◽  
H. Laakso ◽  
J. Backman ◽  
...  
Keyword(s):  
Optical Properties ◽  
Seasonal Variation ◽  
Atmospheric Aerosols ◽  
Single Scattering ◽  
Observation System ◽  
Global Context ◽  
Scattering Coefficients ◽  
Aerosol Absorption ◽  
The Mean ◽  
Winter Time

Abstract. In this paper we introduce new in situ observations of atmospheric aerosols, especially chemical composition, physical and optical properties, on the eastern brink of the heavily polluted Highveld area in South Africa. During the observation period between 11 February 2009 and 31 January 2011, the mean particle number concentration (size range 10–840 nm) was 6310 cm3 and the estimated volume of sub-10 μm particles 9.3 μm3 m−3. The aerosol absorption and scattering coefficients at 637 nm were 8.3 Mm−1 and 49.5 Mm−1, respectively. The mean single-scattering albedo at 637 nm was 0.84 and the Ångström exponent of scattering was 1.5 over the wavelength range 450–635 nm. The mean O3, SO2, NOx and H2S-concentrations were 37.1, 11.5, 15.1 and 3.2 ppb, respectively. The observed range of concentrations was large and attributed to the seasonal variation of sources and regional meteorological effects, especially the anticyclonic re-circulation and strong winter-time inversions. In a global context, the levels of gases and particulates were typical for continental sites with strong anthropogenic influence, but clearly lower than the most polluted areas of south-eastern Asia. Of all pollutants observed at the site, ozone is the most likely to have adverse environmental effects, as the concentrations were high also during the growing season. The measurements presented here will help to close existing gaps in the ground-based global atmosphere observation system, since very little long-term data of this nature is available for southern Africa.

scholarly journals Measurements of aerosol intensive properties over Visakhapatnam, India for 2007

2011 ◽  
Vol 29 (6) ◽  
pp. 973-985 ◽  
Author(s):  
K. Niranjan ◽  
B. Spandana ◽  
T. Anjana Devi ◽  
V. Sreekanth ◽  
B. L. Madhavan
Keyword(s):  
Asymmetry Parameter ◽  
Radiative Forcing ◽  
Single Scattering ◽  
Peninsular India ◽  
Aerosol Radiative Forcing ◽  
Scattering Coefficients ◽  
Aerosol Absorption ◽  
Angular Scattering ◽  
The Asymmetry ◽  
First Time

Abstract. Information on the aerosol intensive properties like Single Scattering Albedo (SSA) and asymmetry parameter are very limited, particularly over the peninsular India, though extensive reports are available on the aerosol bulk properties. In view of the importance of these parameters in evaluating the aerosol radiative forcing, we present for the first time the temporal variation in SSA with measurements on aerosol absorption and scattering coefficients over Visakhapatnam (17.72° N, 83.32° E; located on the east coast of India) for the year 2007. The inferred SSA was in the range of 0.65 and 0.9 with an annual mean of 0.76 ± 0.013 and with a probable value of 0.80, indicating a marginal atmospheric warming over the region. The mixed layer contribution to column Aerosol Optical depth is found to be 35 % in summer while it is well above 35 % in winter, indicating the confinement of aerosol within the boundary layer during winter. The asymmetry parameter which represents the angular scattering in radiative forcing estimation is found to be around 0.65 ± 0.1 for the location. The day to day variability in SSA is found to be well correlated with the variations in surface BC mass concentrations and/or the relative dominance of the fine/coarse mode aerosol. The results are discussed in light of the aerosol physical and optical properties and the asymmetry parameter.

scholarly journals Optical closure experiments for biomass smoke aerosols

2010 ◽  
Vol 10 (3) ◽  
pp. 7469-7494 ◽  
Author(s):  
L. E. Mack ◽  
E. J. T. Levin ◽  
S. M. Kreidenweis ◽  
D. Obrist ◽  
H. Moosmüller ◽  
...  
Keyword(s):  
Optical Properties ◽  
Complex Refractive Index ◽  
Single Scattering ◽  
Size Distributions ◽  
Laboratory Studies ◽  
Biomass Smoke ◽  
Scattering Coefficients ◽  
Aerosol Absorption ◽  
Southeastern Us ◽  
Highly Sensitive

Abstract. The FLAME experiments were a series of laboratory studies of the chemical, physical, and optical properties of fresh smokes from the combustion of wildland fuels that are burned annually in the western and southeastern US. The burns were conducted in the combustion chamber of the USFS Fire Sciences Laboratory in Missoula, Montana. Here we discuss the retrieval of optical properties for a variety of fuels burned in FLAME 2, using nephelometer-measured scattering coefficients, photoacoustically-measured aerosol absorption coefficients, and size distribution measurements. Uncertainties are estimated from the various instrument characteristics and from instrument calibration studies. Our estimates of single scattering albedo for different dry smokes varied from 0.43–0.99, indicative of the wide variations in smoke aerosol chemical composition that were observed. In selected case studies, we retrieved the complex refractive index from the measurements, but show that these are highly sensitive to the uncertainties in measured size distributions.

scholarly journals Optical closure experiments for biomass smoke aerosols

2010 ◽  
Vol 10 (18) ◽  
pp. 9017-9026 ◽  
Author(s):  
L. A. Mack ◽  
E. J. T. Levin ◽  
S. M. Kreidenweis ◽  
D. Obrist ◽  
H. Moosmüller ◽  
...  
Keyword(s):  
Optical Properties ◽  
Complex Refractive Index ◽  
Single Scattering ◽  
Biomass Smoke ◽  
Scattering Coefficients ◽  
Aerosol Absorption ◽  
Southeastern Us ◽  
Highly Sensitive ◽  
The Us ◽  
Us Forest Service

Abstract. A series of laboratory experiments at the Fire Laboratory at Missoula (FLAME) investigated chemical, physical, and optical properties of fresh smoke samples from combustion of wildland fuels that are burned annually in the western and southeastern US The burns were conducted in the combustion chamber of the US Forest Service Fire Sciences Laboratory in Missoula, Montana. Here we discuss retrieval of optical properties for a variety of fuels burned in FLAME 2, using nephelometer-measured scattering coefficients, photoacoustically-measured aerosol absorption coefficients, and size distribution measurements. Uncertainties are estimated from various instrument characteristics and instrument calibration studies. Our estimates of single scattering albedo for different dry smoke samples varied from 0.428 to 0.990, indicative of observed wide variations in smoke aerosol chemical composition. In selected case studies, we retrieved the complex refractive index from measurements but show that these are highly sensitive to uncertainties in measured size distributions.

scholarly journals Vertical profiles of sub-micron aerosol single scattering albedo over Indian region immediately before monsoon onset and during its development: Research from the SWAAMI field campaign

2019 ◽  
Author(s):  
Mohanan R. Manoj ◽  
Sreedharan K. Satheesh ◽  
Krishnaswamy K. Moorthy ◽  
Hugh Coe
Keyword(s):  
Active Phase ◽  
Single Scattering ◽  
Single Scattering Albedo ◽  
Development Research ◽  
Aerosol Absorption ◽  
South West ◽  
Aerosol Scattering ◽  
First Time ◽  
Geographical Locations

Abstract. Vertical structures of aerosol single scattering albedo (SSA), from near the surface through the free troposphere, have been estimated for the first time at distinct geographical locations over the Indian mainland and adjoining oceans, using in-situ measurements of aerosol scattering and absorption coefficients aboard the FAAM BAe-146 aircraft during the South West Asian Aerosol Monsoon Interactions (SWAAMI) campaign from June to July 2016. These are used to examine the spatial variation of SSA profiles and also to characterize its transformation from just prior to the onset of Indian Summer Monsoon (June 2016) to its active phase (July 2016). Very strong aerosol absorption, with SSA values as low as 0.7, persisted in the lower altitudes (

scholarly journals Estimates of aerosol absorption over India using multi-satellite retrieval

2013 ◽  
Vol 31 (10) ◽  
pp. 1773-1778 ◽  
Author(s):  
D. Narasimhan ◽  
S. K. Satheesh
Keyword(s):  
Regional Distribution ◽  
Single Scattering ◽  
Ozone Monitoring Instrument ◽  
Satellite Retrieval ◽  
Aerosol Absorption ◽  
Moderate Resolution ◽  
Indian Landmass ◽  
Resolution Imaging ◽  
Moderate Resolution Imaging Spectroradiometer ◽  
First Time

Abstract. Aerosol absorption is poorly quantified because of the lack of adequate measurements. It has been shown that the Ozone Monitoring Instrument (OMI) aboard EOS-Aura and the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard EOS-Aqua, which fly in formation as part of the A-train, provide an excellent opportunity to improve the accuracy of aerosol retrievals. Here, we follow a multi-satellite approach to estimate the regional distribution of aerosol absorption over continental India for the first time. Annually and regionally averaged aerosol single-scattering albedo over the Indian landmass is estimated as 0.94 ± 0.03. Our study demonstrates the potential of multi-satellite data analysis to improve the accuracy of retrieval of aerosol absorption over land.

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

2016 ◽  
Vol 16 (23) ◽  
pp. 15185-15197 ◽  
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.

scholarly journals Direct radiative effect by brown carbon over the Indo-Gangetic Plain

2015 ◽  
Vol 15 (22) ◽  
pp. 12731-12740 ◽  
Author(s):  
A. Arola ◽  
G. L. Schuster ◽  
M. R. A. Pitkänen ◽  
O. Dubovik ◽  
H. Kokkola ◽  
...  
Keyword(s):  
Winter Season ◽  
Carbonaceous Aerosols ◽  
Radiative Effect ◽  
Gangetic Plain ◽  
Brown Carbon ◽  
Relative Significance ◽  
Aerosol Absorption ◽  
Spectrally Resolved ◽  
First Time ◽  
Indo Gangetic Plain

Abstract. The importance of light-absorbing organic aerosols, often called brown carbon (BrC), has become evident in recent years. However, there have been relatively few measurement-based estimates for the direct radiative effect of BrC so far. In earlier studies, the AErosol RObotic NETwork (AERONET)-measured aerosol absorption optical depth (AAOD) and absorption Angstrom exponent (AAE) were exploited. However, these two pieces of information are clearly not sufficient to separate properly carbonaceous aerosols from dust, while imaginary indices of refraction would contain more and better justified information for this purpose. This is first time that the direct radiative effect (DRE) of BrC is estimated by exploiting the AERONET-retrieved imaginary indices. We estimated it for four sites in the Indo-Gangetic Plain (IGP), Karachi, Lahore, Kanpur and Gandhi College. We found a distinct seasonality, which was generally similar among all the sites, but with slightly different strengths. The monthly warming effect up to 0.5 W m−2 takes place during the spring season. On the other hand, BrC results in an overall cooling effect in the winter season, which can reach levels close to −1 W m−2. We then estimated similarly also the DRE of black carbon and total aerosol, in order to assess the relative significance of the BrC radiative effect in the radiative effects of other components. Even though BrC impact seems minor in this context, we demonstrated that it is not insignificant. Moreover, we demonstrated that it is crucial to perform spectrally resolved radiative transfer calculations to obtain good estimates for the DRE of BrC.

scholarly journals Aerosol light absorption and the role of extremely low volatility organic compounds

2020 ◽  
Vol 20 (19) ◽  
pp. 11625-11637
Author(s):  
Antonios Tasoglou ◽  
Evangelos Louvaris ◽  
Kalliopi Florou ◽  
Aikaterini Liangou ◽  
Eleni Karnezi ◽  
...  
Keyword(s):  
Black Carbon ◽  
Organic Compounds ◽  
Light Absorption ◽  
Absorption Enhancement ◽  
Scanning Mobility Particle Sizer ◽  
Brown Carbon ◽  
Aerosol Absorption ◽  
Aerosol Mass ◽  
Particle Sizer

Abstract. A month-long set of summertime measurements in a remote area in the Mediterranean is used to quantify aerosol absorption and the role of black and brown carbon. The suite of instruments included a high-resolution aerosol mass spectrometer (HR-ToF-AMS) and a scanning mobility particle sizer (SMPS), both coupled to a thermodenuder and an Aethalometer, a photoacoustic extinctiometer (PAX405), and a single particle soot photometer (SP2). The average refractory black carbon (rBC) concentration during the campaign was 0.14 µg m−3, representing 3 % of the fine aerosol mass. The measured light absorption was two or more times higher than that of fresh black carbon (BC). Mie theory indicated that the absorption enhancement due to the coating of BC cores by nonrefractory material could explain only part of this absorption enhancement. The role of brown carbon (BrC) and other non-BC light-absorbing material was then investigated. A good correlation (R2=0.76) between the unexplained absorption and the concentration of extremely low volatility organic compounds (ELVOCs) mass was found.

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