Measurements Of Aerosol Light Absorption Research Articles

Increase in precipitation scavenging contributes to long-term reductions of light-absorbing aerosol in the Arctic

Abstract. We investigated long-term changes using a harmonised 22-year data set of aerosol light absorption measurements, in conjunction with air mass history and aerosol source analysis. The measurements were performed at Zeppelin Observatory, Svalbard, from 2002 to 2023. We report a statistically significant decreasing long-term trend for the light absorption coefficient. However, the last 8 years of 2016–2023 showed a slight increase in the magnitude of the light absorption coefficient for the Arctic haze season. In addition, we observed an increasing trend in the single-scattering albedo from 2002 to 2023. Five distinct source regions, representing different transport pathways, were identified. The trends involving air masses from the five regions showed decreasing absorption coefficients, except for the air masses from Eurasia. We show that the changes in the occurrences of each transport pathway cannot explain the reductions in the absorption coefficient observed at the Zeppelin station. An increase in contributions of air masses from more marine regions, with lower absorption coefficients, is compensated for by an influence from high-emission regions. The proportion of air masses en route to Zeppelin, which have been influenced by active fires, has undergone a noticeable increase starting in 2015. However, this increase has not impacted the long-term trends in the concentration of light-absorbing aerosol. Along with aerosol optical properties, we also show an increasing trend in accumulated surface precipitation experienced by air masses en route to the Zeppelin Observatory. We argue that the increase in precipitation, as experienced by air masses arriving at the station, can explain a quarter of the long-term reduction in the light absorption coefficient. We emphasise that meteorological conditions en route to the Zeppelin Observatory are critical for understanding the observed trends.

Realistic operation of two residential cordwood-fired outdoor hydronic heater appliances—Part 3: Optical properties of black and brown carbon emissions

ABSTRACT Residential biomass combustion is a source of carbonaceous aerosol. Inefficient combustion, particularly of solid fuels produces large quantities of black and brown carbon (BC and BrC). These particle types are important as they have noted effects on climate forcing and human health. One method of measuring these quantities is by measurement of aerosol light-absorption and scattering, which can be performed using an aethalometer and nephelometer, respectively. These instruments are widely deployed in the study of ambient air and are frequently used in air quality modeling and source apportionment studies. In this study, we will describe (1) a method for measuring primary BC and BrC emissions from two residential log-fired wood hydronic heaters and (2) the BC and BrC emission from these devices over a wide range of operating conditions, such as cold-starts, warm-starts, four different levels of output ranging from 15% to 100% maximum rated output, and periods of repeated cycling. The range in flue-gas BC concentrations, measured using an aethalometer at the 880 nanometer (nm) wavelength, were between 5.09 × 102 and 2.24 × 104 micrograms per cubic meter (µg/m3) while the scattering coefficient of the flue-gas, measured by a nephelometer at 880 nm, ranged between 2.20 × 103 and 8.56 × 105 inverse megameters (Mm−1). The BrC concentrations, measured using the 370 nm wavelength of an aethalometer, were between 9.10 × 101 and 3.56 × 104 µg/m3. The calculated Angstrom Absorption Exponent (AAE) of the flue-gas aerosol ranged between 1.54 and 3.63. Performing a comparison between the measured BC concentration and an external particulate matter (PM) concentration showed that overall BC makes up roughly a quarter of the PM emitted by either of the two appliances. Further for both appliances, the cold-start and the test phase immediately following it had the highest BC and BrC concentrations, the highest measured scattering coefficient, as well as a low AAE. Implications: In this work we provide information on the black and brown carbon emissions from outdoor cordwood-fired hydronic heaters. Aethalometer based black carbon measurements are common in atmospheric science, but are uncommonly used in laboratory studies. This work helps to bridge that gap. This data helps to inform the work of modelers and policy makers interested in hydronic heaters and source apportioning biomass combustion emissions.

Humic-like substances (HULIS) in springtime aerosols at a high-altitude background station in the western North Pacific: Source attribution, abundance, and light-absorption

Atmospheric humic-like substances (HULIS) are important components of biomass-burning (BB) emissions and highly associated with light-absorbing organic aerosols (often referred to as brown carbon). This study highlights the importance of BB-emitted HULIS aerosols in peninsular Southeast Asian outflow to the subtropical western North Pacific. We determined various key light-absorbing characteristics of HULIS i.e. mass absorption cross-section (MACHULIS), absorbing component of the refractive index (kHULIS), and absorption Ångström exponent (AAEHULIS) based on ground-based aerosol light absorption measurements along with HULIS concentrations in springtime aerosols at Lulin Atmospheric Background Station (LABS; 2862 m above mean sea level), which is a representative high-altitude remote site in the western North Pacific. Daily variations of HULIS (0.58–12.92 μg m−3) at LABS were mostly linked with the influence from incoming air-masses, while correlations with BB tracers and secondary aerosols indicated the attribution of primary and secondary sources. Stronger light absorption capability of HULIS was clearly evident from MACHULIS and kHULIS values at 370 nm, which were about ~1.5 times higher during BB-dominated days (1.16 ± 0.75 m2 g−1 and 0.05 ± 0.03, respectively) than that during non-BB days (0.77 ± 0.89 m2 g−1 and 0.03 ± 0.04, respectively). Estimates from a simple radiative transfer model showed that HULIS absorption can add as much as 15.13 W g−1 to atmospheric warming, and ~46% more during BB-dominated than non-BB period, highlighting that HULIS light absorption may significantly affect the Earth–atmosphere system and tropospheric photochemistry over the western North Pacific.

Variability of black carbon aerosol concentrations and sources at a Mediterranean coastal region

To investigate the temporal variation of aerosol optical properties and evaluate the main emission sources of black carbon (BC) considering different seasons in a typical Mediterranean coastal environment, a field campaign was conducted during February–July 2019 at the Central Adriatic coastal area. Real-time measurements of aerosol light absorption were continuously obtained using an aethalometer while the Aethalometer model source apportionment data, optimized by using levoglucosan measurements, were evaluated against the modelling results of the LOTOS-EUROS chemical transport model. The measured mean equivalent BC mass concentration of 0.57 ± 0.64 μg m−3 was the lowest observed in the Mediterranean region. BC from fossil fuel (BCff) dominated the area throughout the study period with a maximum in winter and elevated levels by the approaching summer tourist season. Diel variability of BC concentrations from biomass burning (BCbb) was observed during stable winter conditions, with clear morning and evening concentration peaks, consistent with the profile of residential heating by wood burning. Up to 88% of BC concentrations were attributed to European emission sectors, with stationary source combustion, transportation, shipping and agriculture sectors being the most influential contributors. Source apportionment of BC highlighted that, in addition to biomass burning, small combustion fossil fuel sources, including land traffic and shipping, should be more strictly controlled in order to limit BC pollution in Mediterranean coastal areas. This study serves as a basis of comparison for future studies addressing air quality and pollution source apportionment in the Adriatic and/or the Mediterranean coastal regions in efforts of mitigation and adaptation to climate change.

Substantial decreases of light absorption, concentrations and relative contributions of fossil fuel to light-absorbing carbonaceous aerosols attributed to the COVID-19 lockdown in east China.

To prevent spreads of Coronavirus disease-2019 (COVID-19), China adopted the lockdown measures in late January 2020, providing a platform to study the response of air quality and atmospheric chemical and physical properties to strict reduced emissions. In this study, the continuous measurements of aerosol light absorption were conducted in Nanjing, east China, from January 3 to March 31, 2020. Our results showed that the contribution of black carbon (BC) to light absorption at the different wavelengths was more than 75% and the rest light absorption was contributed by brown carbon (BrC), which was mainly originated from primary emissions. Secondary BrC absorption, which was mainly produced by photochemical oxidation, constituted a minor fraction (2–7%) of the total absorption. Compared with the sampling in the pre-lockdown, the significant decreases of BC (43%) and secondary BrC absorption (31%) were found during the lockdown period, resulting in a substantial decrease of solar energy absorbance by 36% on a local scale. The control measures also changed the diurnal variations of light absorption. Due to the reduced emissions, the relative fraction of fossil fuel to BC also dropped from 78% in the pre-lockdown to 71% in the lockdown. The concentrations of BC, PM2.5 and NO2 decreased 1.1 μg m−3, 33 μg m−3 and 9.1 ppb whereas O3 concentration increased 9.0 ppb during the COVID-19 lockdown period. The decreased concentrations of BC, PM2.5 and NO2 were mainly contributed by both emission reduction (51–64%) and meteorological conditions (36–49%). Our results highlighted that the balance of control measures in alleviation of particulate matter (PM) and O3 pollution, and meteorology should be seriously considered for improvement of air quality in this urban city of China.

A single-beam photothermal interferometer for in situ measurements of aerosol light absorption

Abstract. We have developed a novel single-beam photothermal interferometer and present here its application for the measurement of aerosol light absorption. The use of only a single laser beam allows for a compact optical set-up and significantly easier alignment compared to standard dual-beam photothermal interferometers, making it ideal for field measurements. Due to a unique configuration of the reference interferometer arm, light absorption by aerosols can be determined directly – even in the presence of light-absorbing gases. The instrument can be calibrated directly with light-absorbing gases, such as NO2, and can be used to calibrate other light absorption instruments. The detection limits (1σ) for absorption for 10 and 60 s averaging times were determined to be 14.6 and 7.4 Mm−1, respectively, which for a mass absorption cross section of 10 m2 g−1 leads to equivalent black carbon concentration detection limits of 1460 and 740 ng m−3, respectively. The detection limit could be reduced further by improvements to the isolation of the instrument and the signal detection and processing schemes employed.

Aerosol light absorption in a coastal city in Southeast China: Temporal variations and implications for brown carbon

Light-absorbing carbonaceous aerosols including black carbon (BC) and brown carbon (BrC) play significant roles in atmospheric radiative properties. One-year measurements of aerosol light absorption at multi-wavelength were continuously conducted in Xiamen, southeast of China in 2014 to determine the light absorption properties including absorption coefficients (σabs) and absorption Ångström exponent (AAE) in the coastal city. Light absorptions of BC and BrC with their contributions to total light absorption were further quantified. Mean σabs at 370 nm and 880 nm were 56.6 ± 34.3 and 16.5 ± 11.2 Mm−1, respectively. σabs presented a double-peaks diurnal pattern with the maximum in the morning and the minimum in the afternoon. σabs was low in warm seasons and high in cold seasons. AAE ranged from 0.26 to 2.58 with the annual mean of 1.46, implying that both fossil fuel combustion and biomass burning influenced aerosol optical properties. σabs of BrC at 370 nm was 24.0 ± 5.7 Mm−1, contributing 42% to the total absorption. The highest AAE (1.52 ± 0.02) and largest BrC contributions (47% ± 4%) in winter suggested the significant influence of biomass burning on aerosol light absorption. Long-distance air masses passing through North China Plain and the Yangtze River Delta led to high AAE and BrC contributions. High AAE value of 1.46 in July indicated that long-range transport of the air pollutants from intense biomass burning in Southeast Asia would affect aerosol light absorption in Southeast China. The study will improve the understanding of light absorption properties of aerosols and the optical impacts of BrC in China.

Enhanced light absorption due to aerosol particles in ship plumes observed at a seashore site

This study investigates the existence of light-absorbing organic aerosols in ship emissions measured at a seashore site. In-situ measurements of aerosol light absorption at a port of Gangneung located on the East Sea on the Korean Peninsula were made using a multi-wavelength aethalometer for approximately 10 days. Moreover, 7- to 24-hr integrated filter-based measurements were performed to analyze the concentration of water-soluble organic carbon (WSOC). During the study period, short-term excursions of black carbon (BC) concentrations at 880 nm (BC880) and aerosol light absorption coefficients at 370 nm (babs,370) occurred repeatedly, as did absorption Ångström exponent (AAE) values at 370–520 nm (AAE370-520). The babs,370 values during the excursions were 4.8 times higher than the background absorption levels. The AAE370-520 values were close to 1.0 at the onset of the excursion; however, they increased to 1.9–2.3 during the excursion. Furthermore, the contribution of brown carbon (BrC) light absorption at 370 nm (BrC babs,370) to the total light absorption ranged from 2.5–11.0% at the onset of the excursion to 45.2–59.8% during the excursion. The WSOC showed good-to-strong correlation with the babs,370, babs,880, and BrC babs,370, with R2 of 0.63–0.77. This suggests that primary combustion sources contributed to the aerosol light absorption. Enhanced BC880, babs,370, AAE370-520, and contribution of BrC absorption at the seashore site without traffic and industrial sources could be attributed to the light-absorbing organic aerosols in ship emissions. It was observed that absorption by BrC in ship engine exhaust can be as important as BC absorption in shorter visible wavelengths.

Monumental heritage exposure to urban black carbon pollution

In this study, aerosol light-absorption measurements obtained at three sites during a winter campaign were used to analyse and identify the major sources of Black Carbon (BC) particles in and around the Alhambra monument, a UNESCO World Heritage Site that receives over 2 million visitors per year. The Conditional Bivariate Probability Function and the Aethalometer model were employed to identify the main sources of BC particles and to estimate the contributions of biomass burning and fossil fuel emissions to the total Equivalent Black Carbon (EBC) concentrations over the monumental complex. Unexpected high levels of EBC were found at the Alhambra, comparable to those measured in relatively polluted European urban areas during winter. EBC concentrations above 3.0 μg/m3, which are associated with unacceptable levels of soiling and negative public reactions, were observed at Alhambra monument on 13 days from 12 October 2015 to 29 February 2016, which can pose a risk to its long-term conservation and may cause negative social and economic impacts. It was found that road traffic emissions from the nearby urban area and access road to the Alhambra were the main sources of BC particles over the monument. However, biomass burning emissions were found to have very small impact on EBC concentrations at the Alhambra. The highest EBC concentrations were observed during an extended stagnant episode associated with persistent high-pressure systems, reflecting the large impact that can have these synoptic conditions on BC over the Alhambra.

Agricultural fires in the southeastern U.S. during SEAC4RS: Emissions of trace gases and particles and evolution of ozone, reactive nitrogen, and organic aerosol

AbstractEmissions from 15 agricultural fires in the southeastern U.S. were measured from the NASA DC‐8 research aircraft during the summer 2013 Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) campaign. This study reports a detailed set of emission factors (EFs) for 25 trace gases and 6 fine particle species. The chemical evolution of the primary emissions in seven plumes was examined in detail for ~1.2 h. A Lagrangian plume cross‐section model was used to simulate the evolution of ozone (O3), reactive nitrogen species, and organic aerosol (OA). Observed EFs are generally consistent with previous measurements of crop residue burning, but the fires studied here emitted high amounts of SO2and fine particles, especially primary OA and chloride. Filter‐based measurements of aerosol light absorption implied that brown carbon (BrC) was ubiquitous in the plumes. In aged plumes, rapid production of O3, peroxyacetyl nitrate (PAN), and nitrate was observed with ΔO3/ΔCO, ΔPAN/ΔNOy, and Δnitrate/ΔNOyreaching ~0.1, ~0.3, and ~0.3. For five selected cases, the model reasonably simulated O3formation but underestimated PAN formation. No significant evolution of OA mass or BrC absorption was observed. However, a consistent increase in oxygen‐to‐carbon (O/C) ratios of OA indicated that OA oxidation in the agricultural fire plumes was much faster than in urban and forest fire plumes. Finally, total annual SO2, NOx, and CO emissions from agricultural fires in Arkansas, Louisiana, Mississippi, and Missouri were estimated (within a factor of ~2) to be equivalent to ~2% SO2from coal combustion and ~1% NOxand ~9% CO from mobile sources.

Measurement and analysis of black carbon aerosols over a tropical semi-arid station in Kadapa, India

This paper presents aerosol light absorption measurements using a seven channel Aethalometer (AE-42), recorded during September 2011–November 2012 over a tropical semi-arid site in Kadapa, India. The annual average black carbon (BC) mass concentration ([BC]) during the studied period was 2.20±0.78μgm−3 which is in agreement when compared to other sites of similar environment. Strong seasonal variation was observed with high values during winter (2.87±0.81μgm−3) and low in monsoon (1.30±0.31μgm−3) season, which could be attributed to regional synoptic meteorology and long range transport. The two peaks in diurnal variations of [BC] were observed during morning between 06:00 and 08:00h local time (LT) and in the evening around 19:00–21:00h LT, with a minimum peak in the afternoon (~16:00h LT) which is strongly correlated with the boundary layer dynamics, local and regional sources, and associated meteorology. The relationships between measured [BC] and the corresponding meteorological parameters for the studied region were also analysed. The estimated monthly mean spectral absorption coefficient values range from 0.56 to 1.15 with an average of 0.90, which suggests high BC/OC ratio and possible source of emission of aerosols is fossil fuel burning. Trajectory cluster analysis showed significant impact of long range transport of BC aerosols towards the observational site during the period of study.

광음향 및 네펠로미터 방식을 이용한 에어로졸 흡수 및 산란계수 측정

Ambient measurements of aerosol light absorption (σ a ) and scattering coefficients (σ s ) were done at Gosan climate observatory during summer 2008 using a 3-wavelength photoacoustic soot spectrometer (PASS). PASS was deployed photoacoustic method for light absorption and integrated nephelometry for light scattering measurements. The σ a and σ s from PASS were compared with those from co-located aethalometer and nephelometer measurements. The aethalometer measurements of σ a correlated reasonably well with photoacoustic measurements, but the slope of the linear fitting line indicated the PASS measurement values of σa were larger by a factor of 1.53. The nephelometer measurement values of σ s correlated very well with PASS measurements of σ s , with a slope of 1.12 and a small offset. Comparing to the aethalometer measurements, the photoacoustic measurements of σ a didn’t exhibit a significant (i.e., the ratio between aethalometer and PASS increased) change with increasing relative humidity (RH). The ratio of σ s between nephelometer and PASS increased with increasing RH, especially when the RH increased beyond 80%. This apparent increase in σs with RH may be due to the contribution of hygroscopic growth of aerosols.

Estimation of the Deposited Aerosol Particles in Baghdad City, using Image Processing Technique

ABSTRACT In this study, an algorithm was developed to measure the volume and the covered area by the dust particles, and the radius of dust particle deposited for different time hours of the day. Slices transparent glass has been used to collect samples of dust particle deposited for different time of the day in Rusafa area of Baghdad city, were taken digital image of the samples through an optical microscope (EYEPIECE 10X). What have been noticeable are the difference in radii and areas of dust particles deposited as well as the difference in the density of dust particles for each slice according to time that put the slice to deposition. this paper, Keywords Dust particle, Atmospheric Aerosols. 1. INTRODUCTION Air pollution is one of the important problems in latest decades, with increasing use of fuels from oil and natural gas in various fields of life, spread in the environment many air pollutants such as gases resulting from industrial activities or different modes of transport [1].Air pollutants are classified according to the nature of its presence into two main groups: gaseous pollutants and aerosols. An example of gaseous pollutants and hydrocarbons that exist in the form of organic compounds may be gaseous, liquid or solid, such as sulfur oxides, nitrogen oxides and carbon [2]. The aerosol pollutants other are divided into solid and liquid non-permanent, such as the normal dust and pollen. Aerosol sooner or later precipitates out of the air but gases, containing space which launches it and act like the air and will not precipitate [3]. Aerosol light-absorption measurements are important for health, climate, and visibility applications [4]. Michael D. King et al. (1999) [5] Studied the advantages and disadvantages systems of Remote sensing for aerosol application, Where no one sensor system is capable of providing totally unambiguous information. Also a careful intercomparison of derived products from different sensors, to gather with comprehensive network of ground-based sun photometer and sky radiometer systems. W.Partrick Arnottet. al.(2005)[4] exploited the aerosol optics use in experiment develop a model-based calibration scheme for the 7-wavelength aethalometer, and the photo acoustic instrument operating at 532nm is used to evaluate the filter loading effect caused by aerosol light absorption and multiple scattering theory is used to analytically obtain a filter-loading correction function. G. J. Wong et al. (2007) [6] Studied the temporal development for air quality, was develop the image processing technique for enhancing the capability of an internet video surveillance (IVS) camera for real time air quality monitoring, in this technique could to detect particulate mater with diameter less than 10 micrometers(PM10).Xiaolei Yu et. al. (2011) [7] introduced a relationship between aerosol anthropogenic component and air quality in the city of Wuhan, by used satellite remote sensing. A. Bagatet. al. (2013) [8] exploit the aerosol optical depth, Angstrom exponent, single scattering albedo, and polarized phase function have been retrieved from polarized sun-photometer measurements for atmosphere. Where the Angstrom exponent has a meaningful variations respect to the changes in the complex refractive index of the aerosol, and the polarized phase function shows a moderate negative correlation respect to aerosol optical depth and single scattering albedo, so polarized phase function became regarded as a key parameter to characterize the aerosol. In measuring system will be introduced for determine radius, covered area by deposited aerosol particle and deposited aerosol particle volume as a function of day time, will be calculated by using image analysis and computer algorithms.

Impacts of volatilisation on light scattering and filter-based absorption measurements: a case study

Abstract. Aerosol light absorption measurements most commonly rely on filter-based techniques. These methods are influenced by light scattering constituents in the aerosol phase deposited on the filters. The coating of soot by non-absorbing constituents changes the mixing state of soot as the aerosol ages and increase light absorption by the aerosol. Most light scattering constituents in a sub-micron aerosol are volatile by their nature due to their chemical composition and can be volatilized by heating the sample air. The initial mixing state is lost but the remaining light absorption by the aerosol should be by non-coated soot alone. This was studied during a short field campaign with two groups of equipment measuring in parallel for six days in April 2009 at the SMEAR III station in Helsinki. When heated, the light scattering constituents were evaporated thus reducing the single-scattering albedo (ω0) of the aerosol by as much as 0.4. An oven was set to scan different temperatures which revealed the volatility of the urban aerosol at different temperatures as well as the single-scattering albedo's dependence on the non-volatile volume fraction remaining (NVFR). The NVFR was 0.72 ± 0.13, 0.42 ± 0.06 and 0.22 ± 0.05 at 50, 150 and 280 °C respectively. ω0 behaved analogically, it was 0.71 ± 0.05, 0.62 ± 0.06 and 0.42 ± 0.07 at the respective temperatures. We found that absorption coefficients measured at different temperatures showed a temperature dependency possibly indicating initially different mixing states of the non-volatile constituents. By heating the aerosol the mode of the size distribution gets shifted to smaller sizes which in turn changes the filter-based instrument's response due increased penetration depth into the filter by the smaller residual particles. This was compensated for by using size distribution data.

Radiative transfer modeling of filter-based measurements of light absorption by particles: Importance of particle size dependent penetration depth

We present new physical models to interpret the response characteristics of filter-based measurements of aerosol light absorption. They were motivated by a recently found particle size dependence of a systematic bias in absorption measurements that cannot be interpreted by any models reported thus far. A theory of particle filtration by fibrous filter is applied to reproduce the penetration depth of particles into a filter matrix, and the light transmissivity of the matrix is calculated by the use of radiative transfer theory for plane-parallel layers. Optical properties of individual layers are calculated from microphysical properties and the number density of filter fibers and deposited particles. The size-dependent systematic bias in absorption measurement is successfully explained by the particle size dependence of penetration depth into a filter matrix. In practice the physical models developed here are useful for selecting operating conditions and filter matrices for instruments with fewer systematic biases.

Reduction in biomass burning aerosol light absorption upon humidification: roles of inorganically-induced hygroscopicity, particle collapse, and photoacoustic heat and mass transfer

Abstract. Smoke particle emissions from the combustion of biomass fuels typical for the western and southeastern United States were studied and compared under high humidity and ambient conditions in the laboratory. The fuels used were Montana ponderosa pine (Pinus ponderosa), southern California chamise (Adenostoma fasciculatum), and Florida saw palmetto (Serenoa repens). Information on the non-refractory chemical composition of biomass burning aerosol from each fuel was obtained with an aerosol mass spectrometer and through estimation of the black carbon concentration from light absorption measurements at 870 nm. Changes in the optical and physical particle properties under high humidity conditions were observed for hygroscopic smoke particles containing substantial inorganic mass fractions that were emitted from combustion of chamise and palmetto fuels. Light scattering cross sections increased under high humidity for these particles, consistent with the hygroscopic growth measured for 100 nm particles in HTDMA measurements. Photoacoustic measurements of aerosol light absorption coefficients revealed a 20% reduction with increasing relative humidity, contrary to the expectation of light absorption enhancement by the liquid coating taken up by hygroscopic particles. This reduction is hypothesized to arise from two mechanisms: (1) shielding of inner monomers after particle consolidation or collapse with water uptake; (2) the lower case contribution of mass transfer through evaporation and condensation at high relative humidity (RH) to the usual heat transfer pathway for energy release by laser-heated particles in the photoacoustic measurement of aerosol light absorption. The mass transfer contribution is used to evaluate the fraction of aerosol surface covered with liquid water solution as a function of RH.

Bias in Filter-Based Aerosol Light Absorption Measurements Due to Organic Aerosol Loading: Evidence from Laboratory Measurements

Light absorption by soot or nigrosin dye aerosol particles were measured in the laboratory using a particle soot absorption photometer (PSAP) and a photo-acoustic spectrometer (PAS) to assess the influence of non-absorbing organic aerosol (OA) on the PSAP measurements. For the PSAP, particle light absorption is measured after collection on a filter, whereas for the PAS light absorption is measured while the particles remain suspended in the gas phase. OA was generated from the reaction of α -pinene with ozone. It was observed that the presence of this OA in an external mixture of absorbing aerosol and OA can cause an increase in the light absorption measured by the PSAP, relative to that measured by the PAS, by more than a factor of two. This enhancement in the PSAP absorption was found to increase as the amount of OA increased relative to the absorbing compound. Additionally, experiments where absorbing aerosol was deposited on a PSAP filter prior to addition of OA demonstrated that the non-absorbing OA ...

Strong spectral variation of biomass smoke light absorption and single scattering albedo observed with a novel dual‐wavelength photoacoustic instrument

A dual‐wavelength photoacoustic instrument operating at 405 and 870 nm was used during the 2006 Fire Lab at Missoula Experiment to measure light scattering and absorption by smoke from the combustion of a variety of biomass fuels. Simultaneous measurements of aerosol light scattering by reciprocal nephelometry within the instrument's acoustic resonator accompany photoacoustic aerosol light absorption measurements. Single scattering albedo values at 405 nm ranging from 0.37 to 0.95 were measured for different fuel types, and the spectral dependence of absorption was quantified using the Ångström exponent of absorption. An absorption Ångström exponent near unity is commonly observed for motor vehicle emission‐generated black carbon aerosol. For biomass smoke, Ångström exponents as high as 3.5 were found in association with smoke having single scattering albedo near unity. The measurements strongly suggest that light‐absorbing organic material is present in wood smoke. A second single‐wavelength photoacoustic instrument with reciprocal nephelometry was used to quantify aerosol scattering and absorption at 532 nm. Absorption Ångström exponents calculated using 532 and 870 nm data were as large as 2.5 for smoke with single scattering albedos near unity. The spectral variation in optical properties provides insight into the differentiation of aerosols from mobile or industrial sources versus those from biomass burning. Optical properties of biomass smokes could be classified by general fuel type such as flowering shrubs versus pine needle litter.

Using Aerosol Light Absorption Measurements for the Quantitative Determination of Wood Burning and Traffic Emission Contributions to Particulate Matter

A source apportionment study was performed for particulate matter in the small village of Roveredo, Switzerland, where more than 70% of the households use wood burning for heating purposes. A two-lane trans-Alpine highway passes through the village and contributes to the total aerosol burden in the area. The village is located in a steep Alpine valley characterized by strong and persistent temperature inversions during winter, especially from December to February. During two winter and one early spring campaigns, a seven-wavelength aethalometer, high volume (HIVOL) samplers, an Aerodyne quadrupole aerosol mass spectrometer (AMS), an optical particle counter (OPC), and a Sunset Laboratory OCEC analyzer were deployed to study the contribution of wood burning and traffic aerosols to particulate matter. A linear regression model of the carbonaceous particulate mass in the submicrometer size range CM(PM1) as a function of aerosol light absorption properties measured by the aethalometer is introduced to estimate the particulate mass from wood burning and traffic (PM(wb), PM(traffic)). This model was calibrated with analyses from the 14C method using HIVOL filter measurements. These results indicate that light absorption exponents of 1.1 for traffic and 1.8-1.9 for wood burning calculated from the light absorption at 470 and 950 nanometers should be used to obtain agreement of the two methods regarding the relative wood burning and traffic emission contributions to CM(PM1) and also to black carbon. The resulting PM(wb) and PM(traffic) values explain 86% of the variance of the CM(PM1) and contribute, on average, 88 and 12% to CM(PM1), respectively. The black carbon is estimated to be 51% due to wood burning and 49% due to traffic emissions. The average organic carbon/total carbon (OC/TC) values were estimated to be 0.52 for traffic and 0.88 for wood burning particulate emissions.

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

Abstract. Although the definition and measurement techniques for atmospheric "black carbon" ("BC") or "elemental carbon'' ("EC") 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 from (1) spectral aerosol light absorption measurements near specific combustion sources, (2) observations of spectral properties of water extracts of continental aerosol, (3) laboratory studies indicating the formation of light-absorbing organic matter in the atmosphere, and (4) indirectly from the chemical analogy of aerosol species to colored natural humic substances. We show that brown carbon may severely bias measurements of "BC" and "EC" over vast parts of the troposphere, especially those strongly polluted by biomass burning, where the mass concentration of Cbrown is high relative to that of soot carbon. Chemical measurements to determine "EC" are biased by the refractory nature of Cbrown as well as by complex matrix interferences. Optical measurements of "BC" suffer from a number of problems: (1) many of the presently used instruments introduce a substantial bias into the determination of aerosol light absorption, (2) there is no unique conversion factor between light absorption and "EC" or "BC" concentration in ambient aerosols, and (3) the difference in spectral properties between the different types of LAC, as well as the chemical complexity of Cbrown, lead to several conceptual as well as practical complications. We also suggest that due to the sharply increasing 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. We discuss the possible consequences of these effects for our understanding of tropospheric processes, including their influence on UV-irradiance, atmospheric photochemistry and radiative transfer in clouds.