[Show abstract][Hide abstract] ABSTRACT: Black carbon (BC) aerosol has relatively short atmospheric lifetimes yet plays a unique and important role in the Earth's climate system, making it an important short-term climate mitigation target. Globally, biomass burning is the largest source of BC emissions into the atmosphere. This study investigated the mass absorption efficiency (MAE) of biomass burning BC generated by controlled combustion of various wildland fuels during the Fire Laboratory at Missoula Experiments (FLAME). MAE values derived from a photoacoustic spectrometer (∼7.8 m2/g at a wavelength of 532 nm) were in good agreement with those suggested for uncoated BC when the emission ratios of organic carbon (OC) to elemental carbon (EC) were extremely low (i.e., below 0.3). With the increase of OC/EC, two distinct types of biomass smoke were identified. For the first type, MAE exhibited a positive dependence on OC/EC, while the overestimation of the light absorption coefficient (babs) by a filter-based method was less significant and could be estimated by a nearly constant correction factor. For the second type, MAE was biased low and correlated negatively with OC/EC, while the overestimation of babs by the filter-based method was much more significant and showed an apparent OC/EC dependence. This study suggests that BC emission factors determined by the commonly used thermal-optical methods might be sustantially overestimated for some types of biomass burning emissions. Our results also indicate that biomass burning emissions may include some liquid-like organics that can significantly bias filter-based babs measurements.
Full-text · Article · Feb 2016 · Atmospheric Environment
[Show abstract][Hide abstract] ABSTRACT: The significant issue of the classic multiangle data-processing technique is that the height up to which this technique allows the reliable profiling of the searched atmosphere is always significantly less than the maximum operative range of the scanning lidar signals. The existing multiangle inversion methodology does not allow for the proper inversion into optical profiles of the distant range signals measured in and close to zenith. In this study, a data-processing technique is considered which allows for increasing the maximal heights when profiling the atmosphere with scanning lidar; it is achieved by using the auxiliary backscatter near-end solution and the assumption of a constant lidar ratio over high altitudes. Simulated and experimental data are presented that illustrate the specifics of such a combined technique.
[Show abstract][Hide abstract] ABSTRACT: Within minutes after emission, complex photo-chemistry in biomass burning smoke plumes can cause large changes in the concentrations of ozone (O3) and organic aerosol (OA). Being able to understand and simulate this rapid chemical evolution under a wide variety of conditions is a critical part of forecasting the impact of these fires on air quality, atmospheric composition, and climate. Here we use version 2.1 of the Aerosol Simulation Program (ASP) to simulate the evolution of O 3 and secondary organic aerosol (SOA) within a young biomass burning smoke plume from the Williams prescribed fire in chaparral, which was sampled over California in November 2009. We demonstrate the use of a method for simultaneously accounting for the impact of the unidentified intermediate volatility, semi-volatile, and extremely low volatility organic compounds (here collectively called "SVOCs") on the formation of OA (using the Volatility Basis Set – VBS) and O3 (using the concept of mechanistic reactivity). We show that this method can successfully simulate the observations of O3 , OA, NOx , ethylene (C2H4), and OH to within measurement uncertainty using reasonable assumptions about the average chemistry of the unidentified SVOCs. These assumptions were (1) a reaction rate constant with OH of ∼ 1.0E−11 cm3 s−1 ; (2) a significant fraction (up to ∼ 50 %) of the RO2 + NO reaction resulted in fragmentation, rather than functionalization, of the parent SVOC; (3) ∼ 1.1 molecules of O3 were formed for every molecule of SVOC that reacted; (4) ∼ 60 % of the OH that reacted with the unidentified non-methane organic compounds (NMOC) was regenerated as HO2 ; and (5) that ∼ 50 % of the NO that reacted with the SVOC peroxy radicals was lost, presumably to organic nitrate formation. Additional evidence for the fragmentation pathway is provided by the observed rate of formation of acetic acid (CH3COOH), which is consistent with our assumed fragmentation rate. However, the model overestimates peroxyacetyl nitrate (PAN) formation downwind by about 50%, suggesting the need for further refinements to the chemistry. This method could provide a way for classifying different smoke plume observations in terms of the average chemistry of their SVOCs, and could be used to study how the chemistry of these compounds (and the O3 and OA they form) varies between plumes.
Full-text · Article · Jun 2015 · Atmospheric Chemistry and Physics
[Show abstract][Hide abstract] ABSTRACT: Lidar-data processing techniques are analyzed, which allow determining smoke-plume heights and their dynamics and can be helpful for the improvement of smoke dispersion and air quality models. The data processing algorithms considered in the paper are based on the analysis of two alternative characteristics related to the smoke dispersion process: the regularized intercept function, extracted directly from the recorded lidar signal, and the square-range corrected backscatter signal, obtained after determining and subtracting the constant offset in the recorded signal. The analysis is performed using experimental data of the scanning lidar obtained in the area of prescribed fires.
[Show abstract][Hide abstract] ABSTRACT: Biomass fires can significantly degrade regional air quality through the emission of primary aerosols and the
photochemical production of ozone and secondary aerosols. The injection height of smoke from biomass burning into the atmosphere (‘plume rise height’) is one of the critical factors in determining the impact of fire emissions on air quality. Plume rise models are used to simulate plume rise height and prescribe the vertical distribution of fire emissions for input to smoke dispersion and air quality models. While several plume rise models exist, their uncertainties, biases, and application limits when applied to biomass fires are not well characterized. The poor state of model evaluation is due in large part to a lack of appropriate observational datasets. We have initiated a research project to address this critical observation gap. In August of 2013 we performed a multi-agency field experiment designed to obtain the data necessary to improve the air quality models used by agricultural smoke managers in the northwestern United States. In the experiment, the ground-based mobile lidar, developed at the US Forest Service Missoula Fire Science Laboratory, was used to monitor plume rise heights for nine agricultural fires in the northwestern United States. The lidar measurements were compared with plume rise heights calculated with the Briggs equations, which are used in several smoke management tools. Here we present the preliminary evaluation results and provide recommendations regarding
the application of the models to agricultural burning based on lidar measurements made in the vicinity of Walla Walla, Washington, on August 24, 2013.
[Show abstract][Hide abstract] ABSTRACT: The distortions of the inverted lidar signals can be caused by (i) the
constant offset that remains in the backscatter signal after removing
the background component, (ii) the multiplicative distortion component,
which level is related with the lidar signal intensity, and (iii) the
signal noise in the wide wavelength spectra; the latter includes
lowfrequency components, which do not obey common random-noise
statistics. These distortions, even minor, may yield significant
distortions in the retrieved outputs obtained by the inversion of the
lidar signal. Implicit and explicit premises and assumptions required
for any solution of the lidar equation are additional sources of the
uncertainty in the inversion results. There is no reliable way for
checking whether used assumptions are valid, therefore, the lidar signal
inversion can yield significantly biased results. As a result, instead
some statistically mean profile of the atmospheric parameter of interest
with the corresponding probability function, one obtains some
qualitative estimate of the profile with unknown uncertainty, which
depends on the validity of used assumptions. It means that lidar
profiling is not a measurement but a result of some simulation based on
No preview · Article · Sep 2013 · Proceedings of SPIE - The International Society for Optical Engineering
[Show abstract][Hide abstract] ABSTRACT: The direct multiangle solution is considered, which allows improving the scanning lidar-data-inversion accuracy when the requirement of the horizontally stratified atmosphere is poorly met. The signal measured at zenith or close to zenith is used as a core source for extracting optical characteristics of the atmospheric aerosol loading. The multiangle signals are used as auxiliary data to extract the vertical transmittance profile from the zenith signal. Details of the retrieval methodology are considered that eliminate, or at least soften, some specific ambiguities in the multiangle measurements in horizontally heterogeneous atmospheres. Simulated and experimental elastic lidar data are presented that illustrate the essentials of the data-processing technique. Finally, the prospects of the utilization of high-spectral-resolution lidar in the multiangle mode are discussed.
[Show abstract][Hide abstract] ABSTRACT: Biomass burning (BB) is thought to be the largest global source of
primary organic aerosol (OA) and gas-phase semi-volatile organic
compounds, as well as the second largest global source of non-methane
organic compounds (NMOC). Many aspects of biomass burning are still
poorly understood. In recent US field campaigns we sampled the emissions
from 14 fires in California, Arizona and the southeastern US. These
fires ranged in size from 7-1050 ha. Only five of these fires were
detected as MODIS "hotspots" and none registered in the MODIS burned
area product (MCD45). The under-sampling of small fires by satellite
sensors may present challenges for high-resolution (~1 km, ~1 day) fire
emission inventories. We measured emission factors (EF) for >20 major
species in the air for all fires. For 2 fires we measured EF both in the
lofted plume and also at ground level. The smoke measured near the
ground was mostly from residual smoldering combustion and the EF for
NMOC were up to ten times higher than in the lofted plume. Little
information exists on how to weight these very different measurements to
estimate overall emissions. We measured differences between wildfire and
prescribed fire emissions and integrated extensive lab fire EF
measurements with our field results. The atmospheric processing of
biomass burning emissions is also not well understood. Only two field
studies have tracked both the OA and O3 evolution in
Lagrangian fashion in isolated BB plumes. Case 1 was a plume that
evolved in the tropical boundary layer with high actinic flux, OH, and
RH. ΔOA/ΔCO more than doubled in 1.4 hours while
ΔO3/ΔCO reached 15-30%. Case 2, from our recent
field campaign, involved a temperate zone plume that evolved in the free
troposphere with much lower actinic flux, OH, and RH.
ΔOA/ΔCO decreased slightly over ~4 hours as
ΔO3/ΔCO reached ~11%. While many more
measurements are needed, we suggest that the processing environment
plays a significant role in plume evolution and that the fast formation
of OA and O3 observed in the tropics may be more
representative of most BB plumes globally. This implies a major global
biomass burning O3 source and a global secondary OA source of
at least 50-60 Tg/y, which is ~10% of the gas-phase NMOC that are
co-emitted with the primary OA. Our measurements also provided evidence
of ammonium pairing with organic anions and we measured rapid increases
in BC coatings that will increase the BC absorption efficiency,
hygroscopicity, and cloud impacts, while reducing its atmospheric
[Show abstract][Hide abstract] ABSTRACT: Biomass burning (BB) is a major global source of trace gases and particles. Accurately representing the production and evolution of these emissions is an important goal for atmospheric chemical transport models. We measured a suite of gases and aerosols emitted from an 81 hectare prescribed fire in chaparral fuels on the central coast of California, US on 17 November 2009. We also measured physical and chemical changes that occurred in the isolated downwind plume in the first ~4 h after emission. The measurements were carried out onboard a Twin Otter aircraft outfitted with an airborne Fourier transform infrared spectrometer (AFTIR), aerosol mass spectrometer (AMS), single particle soot photometer (SP2), nephelometer, LiCor CO_2 analyzer, a chemiluminescence ozone instrument, and a wing-mounted meteorological probe. Our measurements included: CO_2; CO; NO_x; NH_3; non-methane organic compounds; organic aerosol (OA); inorganic aerosol (nitrate, ammonium, sulfate, and chloride); aerosol light scattering; refractory black carbon (rBC); and ambient temperature, relative humidity, barometric pressure, and three-dimensional wind velocity. The molar ratio of excess O_3 to excess CO in the plume (ΔO_3/ΔCO) increased from −5.13 (±1.13) × 10^(−3) to 10.2 (±2.16) × 10^(−2) in ~4.5 h following smoke emission. Excess acetic and formic acid (normalized to excess CO) increased by factors of 1.73 ± 0.43 and 7.34 ± 3.03 (respectively) over the same time since emission. Based on the rapid decay of C_2H_4 we infer an in-plume average OH concentration of 5.27 (±0.97) × 10^6 molec cm^(−3), consistent with previous studies showing elevated OH concentrations in biomass burning plumes. Ammonium, nitrate, and sulfate all increased over the course of 4 h. The observed ammonium increase was a factor of 3.90 ± 2.93 in about 4 h, but accounted for just ~36% of the gaseous ammonia lost on a molar basis. Some of the gas phase NH_3 loss may have been due to condensation on, or formation of, particles below the AMS detection range. NO_x was converted to PAN and particle nitrate with PAN production being about two times greater than production of observable nitrate in the first ~4 h following emission. The excess aerosol light scattering in the plume (normalized to excess CO_2) increased by a factor of 2.50 ± 0.74 over 4 h. The increase in light scattering was similar to that observed in an earlier study of a biomass burning plume in Mexico where significant secondary formation of OA closely tracked the increase in scattering. In the California plume, however, ΔOA/ΔCO_2 decreased sharply for the first hour and then increased slowly with a net decrease of ~20% over 4 h. The fraction of thickly coated rBC particles increased up to ~85% over the 4 h aging period. Decreasing OA accompanied by increased scattering/particle coating in initial aging may be due to a combination of particle coagulation and evaporation processes. Recondensation of species initially evaporated from the particles may have contributed to the subsequent slow rise in OA. We compare our results to observations from other plume aging studies and suggest that differences in environmental factors such as smoke concentration, oxidant concentration, actinic flux, and RH contribute significantly to the variation in plume evolution observations.
No preview · Article · Nov 2011 · Atmospheric Chemistry and Physics
[Show abstract][Hide abstract] ABSTRACT: We present a modified technique for processing multiangle lidar data that is applicable for relatively clear atmospheres, where the utilization of the conventional Kano–Hamilton method meets significant issues. Our retrieval algorithm allows computing the two-way transmission and the corresponding extinction-coefficient profile in any slope direction searched during scanning. These parameters are obtained from the backscatter term of the Kano–Hamilton solution and the corresponding square-range-corrected signal; the second component of the solution, related with the vertical optical depth, is completely excluded from consideration. The inversion technique was used to process experimental data obtained with the Missoula Fire Sciences Laboratory lidar. Simulated and real experimental data are presented that illustrate the essentials of the data-processing technique and possible variants of the extinction-coefficient profile retrieval.
[Show abstract][Hide abstract] ABSTRACT: We report airborne measurements of emission factors (EF) for trace gases and PM 2.5 made in southern Mexico in March of 2006 on 6 crop residue fires, 3 tropical dry forest fires, 8 savanna fires, 1 garbage fire, and 7 mountain pine-oak forest fires. The savanna fire EF were measured early in the local dry season and when compared to 5 EF measured late in the African dry season they were at least 1.7 times larger for NO x , NH 3 , H 2 , and most non-methane organic compounds. Our measurements suggest that urban deposition and high windspeed may also be associated with significantly elevated NO x EF. When considering all fires sampled, the percentage of particles con-taining soot increased from 15 to 60% as the modified combustion efficiency increased 10 from 0.88 to 0.98. We estimate that about 175 Tg of fuel was consumed by open burn-ing of biomass and garbage and as biofuel (mainly wood cooking fires) in Mexico in 2006. Combining the fuel consumption estimates with our EF measurements suggests that the above combustion sources account for a large fraction of the reactive trace gases and more than 90% of the total primary, fine carbonaceous particles emitted by 15 all combustion sources in Mexico.
[Show abstract][Hide abstract] ABSTRACT: We have measured emission factors for 19 trace gas species and particulate matter (PM2.5) from 14 prescribed fires in chaparral and oak savanna in the southwestern US, as well as conifer forest understory in the southeastern US and Sierra Nevada mountains of California. These are likely the most extensive emission factor field measurements for temperate biomass burning to date and the only published emission factors for temperate oak savanna fuels. This study helps to close the gap in emissions data available for temperate zone fires relative to tropical biomass burning. We present the first field measurements of the biomass burning emissions of glycolaldehyde, a possible precursor for aqueous phase secondary organic aerosol formation. We also measured the emissions of phenol, another aqueous phase secondary organic aerosol precursor. Our data confirm previous observations that urban deposition can impact the NOx emission factors and thus subsequent plume chemistry. For two fires, we measured both the emissions in the convective smoke plume from our airborne platform and the unlofted residual smoldering combustion emissions with our ground-based platform. The smoke from residual smoldering combustion was characterized by emission factors for hydrocarbon and oxygenated organic species that were up to ten times higher than in the lofted plume, including high 1,3-butadiene and isoprene concentrations which were not observed in the lofted plume. This should be considered in modeling the air quality impacts for smoke that disperses at ground level. We also show that the often ignored unlofted emissions can significantly impact estimates of total emissions. Preliminary evidence suggests large emissions of monoterpenes in the residual smoldering smoke. These data should lead to an improved capacity to model the impacts of biomass burning in similar temperate ecosystems.
Full-text · Article · Jun 2011 · ATMOSPHERIC CHEMISTRY AND PHYSICS
[Show abstract][Hide abstract] ABSTRACT: Smog chamber experiments were conducted to investigate the chemical and physical transformations of organic aerosol (OA) during photo-oxidation of open biomass burning emissions. The experiments were carried out at the US Forest Service Fire Science Laboratory as part of the third Fire Lab at Missoula Experiment (FLAME III). We investigated emissions from 12 different fuels commonly burned in North American wildfires. The experiments feature atmospheric and plume aerosol and oxidant concentrations; aging times ranged from 3 to 4.5 h. OA production, expressed as a mass enhancement ratio (ratio of OA to primary OA (POA) mass), was highly variable. OA mass enhancement ratios ranged from 2.9 in experiments where secondary OA (SOA) production nearly tripled the POA concentration to 0.7 in experiments where photo-oxidation resulted in a 30 % loss of the OA mass. The campaign-average OA mass enhancement ratio was 1.7 ± 0.7 (mean ± 1sigma); therefore, on average, there was substantial SOA production. In every experiment, the OA was chemically transformed. Even in experiments with net loss of OA mass, the OA became increasingly oxygenated and less volatile with aging, indicating that photo-oxidation transformed the POA emissions. Levoglucosan concentrations were also substantially reduced with photo-oxidation. The transformations of POA were extensive; using levoglucosan as a tracer for POA, unreacted POA only contributed 17 % of the campaign-average OA mass after 3.5 h of exposure to typical atmospheric hydroxyl radical (OH) levels. Heterogeneous reactions with OH could account for less than half of this transformation, implying that the coupled gas-particle partitioning and reaction of semi-volatile vapors is an important and potentially dominant mechanism for POA processing. Overall, the results illustrate that biomass burning emissions are subject to extensive chemical processing in the atmosphere, and the timescale for these transformations is rapid.
[Show abstract][Hide abstract] ABSTRACT: Essentials for investigating smoke plume characteristics with scanning lidar are discussed. Particularly, we outline basic principles for determining dynamics, heights, and optical properties of smoke plumes and layers in wildfire-polluted atmospheres. Both simulated and experimental data obtained in vicinities of wildfires with a two-wavelength scanning lidar are considered.
Full-text · Article · Jan 2011 · Romanian Journal of Physics
[Show abstract][Hide abstract] ABSTRACT: The upper height of a region of intense backscatter with a poorly defined boundary between this region and a region of clear air above it is found as the maximal height where aerosol heterogeneity is detectable, that is, where it can be discriminated from noise. The theoretical basis behind the retrieval technique and the corresponding lidar-data-processing procedures are discussed. We also show how such a technique can be applied to one-directional measurements. Examples of typical results obtained with a scanning lidar in smoke-polluted atmospheres and experimental data obtained in an urban atmosphere with a vertically pointing lidar are presented.
[Show abstract][Hide abstract] ABSTRACT: Wildfires are a significant fraction of global biomass burning and a major source of trace gas and particle emissions in the atmosphere. Understanding the air quality and climate implications of wildfires is difficult since the emissions undergo complex transformations due to aging processes during transport away from the source. As part of the third Fire Lab at Missoula Experiment (FLAME III), we investigated the oxidative aging of smoke from combustion of 12 different types of vegetation commonly burned in North American wildfires. In these photochemical chamber experiments, we quantified the evolution of reactive trace gases and particles, with a focus on the chemistry contributing to changes in the organic aerosol (OA) concentration. Factors such as precursor VOC concentrations, oxidant exposure, and the role of NOx were considered. The results illustrate the complex and variable nature of biomass burning emissions, since none of these factors alone account for the wide range of OA enhancements that were observed. For example, in some experiments, a net decrease of up to 30% in the OA concentration was observed, while in others, the OA concentration increased by a factor of three over the course of aging due to secondary OA (SOA) production. Despite this variability, all experiments showed significant physical (e.g., changes in aerosol volatility) and chemical (e.g., changes in oxidation) transformations in the OA due to oxidation. Overall, the results demonstrate that traditional definitions of POA and SOA continue to blur in many systems, and that processes like partitioning and heterogeneous chemistry can have the most significant effect on the evolution of biomass burning aerosol.
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] ABSTRACT: During the Fire Laboratory at Missoula Experiments (FLAME), we studied the physical, chemical, and optical properties of biomass burning smoke from the laboratory combustion of various wildland fuels. A good understanding of these properties is important in determining the radiative effects of biomass burning aerosols, with impacts on both local and regional visibility and global climate. We measured aerosol size distributions with two instruments: a differential mobility particle sizer (DMPS) and an optical particle counter (OPC). Volume size distributions from different burns varied from monomodal to multimodal, with geometric mean diameters ranging from 0.20–0.57 μm and geometric standard deviations ranging from 1.68–2.97. By reconciling the differences between the two sizing instruments, we estimated aerosol effective refractive indices with values ranging from 1.41 to 1.61. We reconstructed aerosol chemical composition for each burn using data from filters collected and analyzed with the Interagency Monitoring of Protected Visual Environments (IMPROVE) samplers and protocols. Aerosols were generally comprised of carbon with organic species accounting for the largest mass fraction in most cases. We used composition data to calculate aerosol density, which ranged from 1.22–1.92 g cm−3, and real and imaginary refractive indices, which had ranges of 1.55–1.80 and 0.01–0.50 respectively. Aerosol physical, chemical, and optical characterizations were combined to calculate dry mass scattering (MSE) and absorption (MAE) efficiencies at 532 nm. These parameters had values between 1.6–5.7 m2 g−1 and 0.04–0.94 m2 g−1.
Full-text · Article · Sep 2010 · Journal of Geophysical Research Atmospheres