scholarly journals Deriving brown carbon from multiwavelength absorption measurements: method and application to AERONET and Aethalometer observations

2016 ◽  
Vol 16 (19) ◽  
pp. 12733-12752 ◽  
Author(s):  
Xuan Wang ◽  
Colette L. Heald ◽  
Arthur J. Sedlacek ◽  
Suzane S. de Sá ◽  
Scot T. Martin ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Cape Cod ◽  
Ambient Atmosphere ◽  
Brown Carbon ◽  
Aerosol Absorption ◽  
Multiple Wavelength ◽  
Radiative Impact ◽  
Wavelength Absorption ◽  
Photochemical Aging ◽  
Absorption Measurements

Abstract. The radiative impact of organic aerosols (OA) is a large source of uncertainty in estimating the global direct radiative effect (DRE) of aerosols. This radiative impact includes not only light scattering but also light absorption from a subclass of OA referred to as brown carbon (BrC). However, the absorption properties of BrC are poorly understood, leading to large uncertainties in modeling studies. To obtain observational constraints from measurements, a simple absorption Ångström exponent (AAE) method is often used to separate the contribution of BrC absorption from that of black carbon (BC). However, this attribution method is based on assumptions regarding the spectral dependence of BC that are often violated in the ambient atmosphere. Here we develop a new AAE method which improves upon previous approaches by using the information from the wavelength-dependent measurements themselves and by allowing for an atmospherically relevant range of BC properties, rather than fixing these at a single assumed value. We note that constraints on BC optical properties and mixing state would help further improve this method. We apply this method to multiwavelength absorption aerosol optical depth (AAOD) measurements at AERONET sites worldwide and surface aerosol absorption measurements at multiple ambient sites. We estimate that BrC globally contributes up to 40 % of the seasonally averaged absorption at 440 nm. We find that the mass absorption coefficient of OA (OA-MAC) is positively correlated with the BC ∕ OA mass ratio. Based on the variability in BC properties and BC ∕ OA emission ratio, we estimate a range of 0.05–1.5 m2 g−1 for OA-MAC at 440 nm. Using the combination of AERONET and OMI UV absorption observations we estimate that the AAE388∕440 nm for BrC is generally  ∼ 4 worldwide, with a smaller value in Europe (< 2). Our analyses of observations at two surface sites (Cape Cod, to the southeast of Boston, and the GoAmazon2014/5 T3 site, to the west of Manaus, Brazil) reveal no significant relationship between BrC absorptivity and photochemical aging in urban-influenced conditions. However, the absorption of BrC measured during the biomass burning season near Manaus is found to decrease with photochemical aging with a lifetime of  ∼ 1 day. This lifetime is comparable to previous observations within a biomass burning plume but much slower than estimated from laboratory studies. Given the large uncertainties associated with AERONET retrievals of AAOD, the most challenging aspect of our analysis is that an accurate, globally distributed, multiple-wavelength aerosol absorption measurement dataset is unavailable at present. Thus, achieving a better understanding of the properties, evolution, and impacts of global BrC will rely on the future deployment of accurate multiple-wavelength absorption measurements to which AAE methods, such as the approach developed here, can be applied.

scholarly journals Deriving Brown Carbon from Multi-Wavelength Absorption Measurements: Method and Application to AERONET and Surface Observations

2016 ◽  
Author(s):  
Xuan Wang ◽  
Colette L. Heald ◽  
Arthur J. Sedlacek ◽  
Suzane S. de Sá ◽  
Scot T. Martin ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Cape Cod ◽  
Ambient Atmosphere ◽  
Brown Carbon ◽  
Radiative Impact ◽  
Multi Wavelength ◽  
Modelling Studies ◽  
Wavelength Absorption ◽  
Photochemical Aging ◽  
Absorption Measurements

Abstract. The radiative impact of organic aerosols (OA) is a large source of uncertainty in estimating the global direct radiative effect (DRE) of aerosols. This radiative impact includes not only light scattering but also light absorption from a subclass of OA referred to as brown carbon (BrC). However the absorption properties of BrC are poorly understood leading to large uncertainties in modelling studies. To obtain observational constraints from measurements, a simple Absorption Ångström Exponent (AAE) method is often used to separate the contribution of BrC absorption from that of black carbon (BC). However, this attribution method is based on assumptions regarding the spectral dependence of BC that are often violated in the ambient atmosphere. Here we develop a new method that decreases the uncertainties associated with estimating BrC absorption. By applying this method to multi-wavelength absorption aerosol optical depth (AAOD) measurements at AERONET sites worldwide and surface aerosol absorption measurements at multiple ambient sites, we estimate that BrC globally contributes 6–40 % of the absorption at 440 nm. We find that the mass absorption coefficient of OA (OA-MAC) is positively correlated with BC / OA mass ratio. Based on the variability of BC properties and BC / OA emission ratio, we estimate a range of 0.05–1.2 m2/g for OA-MAC at 440 nm. Using the combination of AERONET and OMI UV absorption observations we estimate that the AAE388/440 nm for BrC is generally ~ 4 world-wide, with a smaller value in Europe (< 2). Our analyses of two surface sites (Cape Cod, to the southeast of Boston, and the GoAmazon2014/5 T3 site, to the west of Manaus, Brazil) reveal no significant relationship between BrC absorptivity and photochemical aging in typical urban-influenced conditions. However, the absorption of BrC measured during the biomass burning season near Manaus is found to decrease with photochemical aging with a lifetime of ~ 1 day. This lifetime is comparable to previous observations within a biomass burning plume but much slower than estimated from laboratory studies.

scholarly journals Evaluating biases in filter-based aerosol absorption measurements using photoacoustic spectroscopy

2019 ◽  
Vol 12 (6) ◽  
pp. 3417-3434 ◽  
Author(s):  
Nicholas W. Davies ◽  
Cathryn Fox ◽  
Kate Szpek ◽  
Michael I. Cotterell ◽  
Jonathan W. Taylor ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Photoacoustic Spectroscopy ◽  
Strong Dependence ◽  
Single Scattering ◽  
Aerosol Absorption ◽  
Aerosol Mass ◽  
Correction Scheme ◽  
Measurement Biases ◽  
Absorption Photometer ◽  
Absorption Measurements

Abstract. Biases in absorption coefficients measured using a filter-based absorption photometer (Tricolor Absorption Photometer, or TAP) at wavelengths of 467, 528 and 652 nm are evaluated by comparing to measurements made using photoacoustic spectroscopy (PAS). We report comparisons for ambient sampling covering a range of aerosol types including urban, fresh biomass burning and aged biomass burning. Data are also used to evaluate the performance of three different TAP correction schemes. We found that photoacoustic and filter-based measurements were well correlated, but filter-based measurements generally overestimated absorption by up to 45 %. Biases varied with wavelength and depended on the correction scheme applied. Optimal agreement to PAS data was achieved by processing the filter-based measurements using the recently developed correction scheme of Müller et al. (2014), which consistently reduced biases to 0 %–18 % at all wavelengths. The biases were found to be a function of the ratio of organic aerosol mass to light-absorbing carbon mass, although applying the Müller et al. (2014) correction scheme to filter-based absorption measurements reduced the biases and the strength of this correlation significantly. Filter-based absorption measurement biases led to aerosol single-scattering albedos that were biased low by values in the range 0.00–0.07 and absorption Ångström exponents (AAEs) that were in error by ± (0.03–0.54). The discrepancy between the filter-based and PAS absorption measurements is lower than reported in some earlier studies and points to a strong dependence of filter-based measurement accuracy on aerosol source type.

scholarly journals Comparison of different Aethalometer correction schemes and a reference multi-wavelength absorption technique for ambient aerosol data

2017 ◽  
Vol 10 (8) ◽  
pp. 2837-2850 ◽  
Author(s):  
Jorge Saturno ◽  
Christopher Pöhlker ◽  
Dario Massabò ◽  
Joel Brito ◽  
Samara Carbone ◽  
...  
Keyword(s):  
Wavelength Dependence ◽  
Absorption Coefficients ◽  
Multiple Wavelength ◽  
Filter Loading ◽  
Multi Wavelength ◽  
Online Measurements ◽  
Loading Effects ◽  
Wavelength Absorption ◽  
Absorption Photometer ◽  
Absorption Measurements

Abstract. Deriving absorption coefficients from Aethalometer attenuation data requires different corrections to compensate for artifacts related to filter-loading effects, scattering by filter fibers, and scattering by aerosol particles. In this study, two different correction schemes were applied to seven-wavelength Aethalometer data, using multi-angle absorption photometer (MAAP) data as a reference absorption measurement at 637 nm. The compensation algorithms were compared to five-wavelength offline absorption measurements obtained with a multi-wavelength absorbance analyzer (MWAA), which serves as a multiple-wavelength reference measurement. The online measurements took place in the Amazon rainforest, from the wet-to-dry transition season to the dry season (June–September 2014). The mean absorption coefficient (at 637 nm) during this period was 1.8 ± 2.1 Mm−1, with a maximum of 15.9 Mm−1. Under these conditions, the filter-loading compensation was negligible. One of the correction schemes was found to artificially increase the short-wavelength absorption coefficients. It was found that accounting for the aerosol optical properties in the scattering compensation significantly affects the absorption Ångström exponent (åABS) retrievals. Proper Aethalometer data compensation schemes are crucial to retrieve the correct åABS, which is commonly implemented in brown carbon contribution calculations. Additionally, we found that the wavelength dependence of uncompensated Aethalometer attenuation data significantly correlates with the åABS retrieved from offline MWAA measurements.

scholarly journals Evaluating biases in filter-based aerosol absorption measurements using photoacoustic spectroscopy

2019 ◽  
Author(s):  
Nicholas W. Davies ◽  
Cathryn Fox ◽  
Kate Szpek ◽  
Michael I. Cotterell ◽  
Jonathan W. Taylor ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Photoacoustic Spectroscopy ◽  
Strong Dependence ◽  
Single Scattering ◽  
Aerosol Absorption ◽  
Aerosol Mass ◽  
Correction Scheme ◽  
Measurement Biases ◽  
Absorption Photometer ◽  
Absorption Measurements

Abstract. Biases in absorption coefficients measured using a filter-based absorption photometer (Tricolor Absorption Photometer, or TAP) at wavelengths of 467, 528 and 652 nm are evaluated by comparing to measurements made using photoacoustic spectroscopy (PAS). We report comparisons for ambient sampling covering a range of aerosol types including urban, fresh biomass burning and aged biomass burning. Data are also used to evaluate the performance of three different TAP correction schemes. We found that photoacoustic and filter-based measurements were well correlated, but filter-based measurements generally overestimated absorption by up to 45 %. Biases varied with wavelength and depended on the correction scheme applied. Optimal agreement to PAS data was achieved by processing the filter-based measurements using the recently developed correction scheme of Müller et al. (2014), which consistently reduced biases to 0–17 % at all wavelengths. The biases were found to be a function of the ratio of organic aerosol mass to light-absorbing carbon mass although applying the Müller et al. (2014) correction scheme to filter-based absorption measurements reduced the biases and the strength of this correlation significantly. Filter-based absorption measurement biases led to aerosol single-scattering albedos that were biased low by up to 0.07 and absorption Ångström exponents (AAE) that were in error by ±0.54. The discrepancy between the filter-based and PAS absorption measurements is lower than reported in some earlier studies, and points to a strong dependence of filter-based measurement accuracy on aerosol source type.

scholarly journals Combining POLDER-3 satellite observations and WRF-Chem numerical simulations to derive biomass burning aerosol properties over the Southeast Atlantic region

2021 ◽  
Author(s):  
Alexandre Siméon ◽  
Fabien Waquet ◽  
Jean-Christophe Péré ◽  
Fabrice Ducos ◽  
François Thieuleux ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Biomass Burning ◽  
Climate Models ◽  
Single Scattering ◽  
Satellite Observations ◽  
Biomass Combustion ◽  
Absorption Properties ◽  
Brown Carbon ◽  
Aerosol Absorption ◽  
Physico Chemical

Abstract. Aerosol absorption is a key property to assess the radiative impacts of aerosols on climate at both global and regional scales. The aerosol physico-chemical and optical properties remain not sufficiently constrained in climate models, with difficulties to properly represent both the aerosol load and their absorption properties in clear and cloudy scenes, especially for absorbing biomass burning aerosols (BBA). In this study we focus on biomass burning (BB) particle plumes transported above clouds over the Southeast Atlantic (SEA) region off the southwest coast of Africa, in order to improve the representation of their physico-chemical and absorption properties. The methodology is based on aerosol regional numerical simulations from the WRF-Chem coupled meteorology-chemistry model combined with a detailed inventory of BB emissions and various sets of innovative aerosol remote sensing observations, both in clear and cloudy skies from the POLDER-3/PARASOL space sensor. Current literature indicates that some organic aerosol compounds (OC) called "brown carbon" (BrOC), primarily emitted by biomass combustion absorb the ultraviolet-blue radiation more efficiently than pure black carbon (BC). We exploit this specificity by comparing the spectral dependence of the aerosol single scattering albedo (SSA) derived from the POLDER-3 satellite observations in the 443–1020 nm wavelength range with the SSA simulated for different proportions of BC, OC and BrOC at the source level, considering the homogeneous internal mixing state of particles. These numerical simulation experiments are based on two main constraints: maintaining a realistic aerosol optical depth both in clear and above cloudy scenes and a realistic BC/OC mass ratio. Modelling experiments are presented and discussed to link the chemical composition with the absorption properties of BBA and to provide estimates of the relative proportions of black, organic and brown carbon in the African BBA plumes transported over the SEA region for July 2008. The absorbing fraction of organic aerosols in the BBA plumes, i.e., BrOC, is estimated at 2 to 3 %. The simulated mean SSA are 0.81 (565 nm) and 0.84 (550 nm) in clear and above cloudy scenes respectively, in good agreement with those retrieved by POLDER-3 (0.85 ± 0.05 at 565 nm in clear-sky and at 550 nm above clouds) for the studied period.

Contribution of residential wood burning to wintertime air pollution in an urban area

2021 ◽  
Author(s):  
Christos Kaltsonoudis ◽  
Kalliopi Florou ◽  
John Kodros ◽  
Spiro Jorga ◽  
Christina Vasilakopoulou ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
Biomass Burning ◽  
Low Cost ◽  
Proton Transfer Reaction ◽  
Aerosol Size Distribution ◽  
Aerosol Composition ◽  
Brown Carbon ◽  
Aerosol Absorption ◽  
Aerosol Mass ◽  
Wood Burning

&lt;p&gt;&amp;#932;he composition of wintertime urban air in Patras, Greece was investigated during early 2020 focusing on the role of biomass burning. A high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and a Proton Transfer-Reaction Mass Spectrometer (PTR-MS) were deployed. Additionally continuous measurements of the aerosol size distribution from 10 nm to 10 &amp;#956;m were performed, as well as measurements of the size-resolved aerosol composition using a Micro-Orifice Uniform-Deposit Impactor, black carbon (BC) concentrations using an SP2, aerosol absorption, brown carbon concentrations, and reactive oxygen species (ROS). A number of low-cost sensors for particles and vapors was also deployed in the city.&lt;/p&gt;&lt;p&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; The PM&lt;sub&gt;2.5 &lt;/sub&gt;concentration peaked during the early evening reaching up to 150 &amp;#181;g m&lt;sup&gt;-3&lt;/sup&gt;. PM&lt;sub&gt;1&lt;/sub&gt; aerosol (23 &amp;#181;g m&lt;sup&gt;-3&lt;/sup&gt; on average) was mainly composed of organics (69%) with the rest being BC (11%), sulphate (10%), nitrate (5%), ammonium (4%) and chloride (1%). Positive Matrix Factorization (PMF) of the measurements of the AMS indicated that biomass burning due to residential heating was the dominant source of PM&lt;sub&gt;1 &lt;/sub&gt;during the campaign accounting for 53% of the total OA with the rest being the oxygenated organic aerosol (&amp;#927;&amp;#927;&amp;#913;) at 25%, the cooking OA (COA) at 12% and the traffic related hydrocarbon-like OA (HOA) at 10%.&lt;/p&gt;&lt;p&gt;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160;&amp;#160; The biomass burning contribution was also evident in several volatile organic compounds (VOCs) detected by the PTR-MS. Biogenic species such as isoprene and the monoterpenes showed clear relation to wood burning, while most of the aromatic compounds were related both to traffic and wood burning. The latter was also true for other gas species measured such as CO, NO&lt;sub&gt;x &lt;/sub&gt;etc. Biomass burning was also a major contributor to the ROS measured as well as the brown carbon.&lt;/p&gt;

scholarly journals Black carbon or brown carbon? The nature of light-absorbing carbonaceous aerosols

2006 ◽  
Vol 6 (3) ◽  
pp. 3419-3463 ◽  
Author(s):  
M. O. Andreae ◽  
A. Gelencsér
Keyword(s):  
Black Carbon ◽  
Measurement Methods ◽  
Carbonaceous Aerosols ◽  
Carbonaceous Matter ◽  
Scientific Controversy ◽  
Laboratory Studies ◽  
Brown Carbon ◽  
Aerosol Absorption ◽  
Wavelength Light ◽  
Absorption Measurements

Abstract. Although the definition and measurement methods of atmospheric ''black carbon'' (''BC'') have long been subjects of scientific controversy, the recent discovery of light-absorbing carbon that is not black (''brown carbon, Cbrown'') makes it imperative to reassess and redefine the components that make up light-absorbing carbonaceous matter (LAC) in the atmosphere. Evidence for the atmospheric presence of Cbrown comes directly from aerosol absorption measurements near specific combustion sources, from observations of spectral properties of water extracts of continental aerosol, from laboratory studies indicating the formation of light-absorbing organic matter in the atmosphere, and indirectly from the chemical analogy of aerosol species to colored natural humic substances. We show that these species may severely bias measurements of ''BC'' and ''EC'' over vast parts of the troposphere, where mass concentration of Cbrown is high relative to that of combustion soot. We also imply that due to the strongly skewed absorption of Cbrown towards the UV, single-wavelength light absorption measurements may not be adequate for the assessment of absorption of solar radiation in the troposphere. The possible consequences of these effects on our understanding of tropospheric processes are discussed.

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