Cloud condensation nucleation activity of biomass burning aerosol (original) (raw)
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Geophysical Research Letters, 2012
[1] Experiments were performed in an environmental chamber to characterize the effects of photo-chemical aging on biomass burning emissions. Photo-oxidation of dilute exhaust from combustion of 12 different North American fuels induced significant new particle formation that increased the particle number concentration by a factor of four (median value). The production of secondary organic aerosol caused these new particles to grow rapidly, significantly enhancing cloud condensation nuclei (CCN) concentrations. Using inputs derived from these new data, global model simulations predict that nucleation in photo-chemically aging fire plumes produces dramatically higher CCN concentrations over widespread areas of the southern hemisphere during the dry, burning season (Sept.-Oct.), improving model predictions of surface CCN concentrations. The annual indirect forcing from CCN resulting from nucleation and growth in biomass burning plumes is predicted to be À0.2 W m À2 , demonstrating that this effect has a significant impact on climate that has not been previously considered.
Journal of Geophysical Research, 2006
1] During May of 2003, smoke from fires on the Yucatan Peninsula was transported across the Gulf of Mexico and into Texas where it caused a significant enhancement in measured aerosol concentrations. The 24-hour average PM2.5 concentration measured in Austin on 10 May was 50.1 mg/m 3 , which was more than twice that of the highest daily average concentration measured during any other month in 2003. During this event, a differential mobility analyzer/tandem differential mobility analyzer (DMA/TDMA) system was used to characterize the size distribution and size-resolved hygroscopicity and volatility of the aerosol. The hygroscopicity data were used to isolate the less hygroscopic biomass burning particles from other aerosol types. Biomass burning aerosol-only size distributions were then constructed by coupling the size-resolved fraction of particles attributed to the fires with the overall size distribution. These distributions, and the aerosol properties derived from the TDMA data, were used to examine the impact of the smoke on predicted cloud condensation nuclei (CCN) spectra. The influence of the smoke on cloud droplet concentrations and the influence of other aerosol types present on the activation efficiency of the smoke were evaluated using a cloud parcel model. For a subset of the updraft speeds considered, the model predicted that the cloud droplet concentration would sometimes be lower when both smoke and pollution aerosols entered cloud relative to that when only smoke was present. Whereas these cases in which an increased aerosol concentration resulted in a decreased cloud droplet concentration were rare, the inclusion of the pollution aerosol in the model always reduced the activation efficiency of the smoke aerosol, which would influence both its evolution during transport and its atmospheric removal rate.
Atmospheric Chemistry and Physics, 2017
Residential biofuel combustion is an important source of aerosols and gases in the atmosphere. The change in cloud characteristics due to biofuel burning aerosols is uncertain, in part, due to the uncertainty in the added number of cloud condensation nuclei (CCN) from biofuel burning. We provide estimates of the CCN activity of biofuel burning aerosols by explicitly modeling plume dynamics (coagulation, condensation, chemical reactions, and dilution) in a young biofuel burning plume from emission until plume exit, defined here as the condition when the plume reaches ambient temperature and specific humidity through entrainment. We found that aerosol-scale dynamics affect CCN activity only during the first few seconds of evolution, after which the CCN efficiency reaches a constant value. Homogenizing factors in a plume are co-emission of semi-volatile organic compounds (SVOCs) or emission at small particle sizes; SVOC co-emission can be the main factor determining plume-exit CCN for hydrophobic or small particles. Coagulation limits emission of CCN to about 10 16 per kilogram of fuel. Depending on emission factor, particle size, and composition, some of these particles may not activate at low supersaturation (s sat). Hygroscopic Aitken-mode particles can contribute to CCN through self-coagulation but have a small effect on the CCN activity of accumulation-mode particles, regardless of composition differences. Simple models (monodisperse coagulation and average hygroscopicity) can be used to estimate plume-exit CCN within about 20 % if particles are unimodal and have homogeneous composition, or when particles are emitted in the Aitken mode even if they are not homogeneous. On the other hand, if externally mixed particles are emitted in the accumulation mode without SVOCs, an average hygroscopicity overestimates emitted CCN by up to a factor of 2. This work has identified conditions under which particle populations become more homogeneous during plume processes. This homogenizing effect requires the components to be truly co-emitted, rather than sequentially emitted.
“Missing” cloud condensation nuclei in peat smoke
Geophysical Research Letters, 2005
We characterized particulate emissions from vegetation fires by burning Indonesian and German peat and other biomass fuels in a controlled laboratory setting. By measuring cloud condensation nuclei (CCN) both as a function of particle diameter (d(p)) and supersaturation ( S), we discovered particles in peat smoke that were not activated to cloud droplets at high S (1.6\%). These hydrophobic particles
Cloud condensation nuclei from biomass burning
1991
Aircraft measurements of cloud condensation nuclei (CCN) during the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) were conducted over the Southwestern Amazon region in September-October 2002, to emphasize the dry-to-wet transition season. The CCN concentrations were measured for values within the range 0.1-1.0% of supersaturation. The CCN concentration inside the boundary layer revealed a general decreasing trend during the transition from the end of the dry season to the onset of the wet season. Clean and polluted areas showed large differences. The differences were not so strong at high levels in the troposphere and there was evidence supporting the semi-direct aerosol effect in suppressing convection through the evaporation of clouds by aerosol absorption. The measurements also showed a diurnal cycle following biomass burning activity. Although biomass burning was the most important source of CCN, it was seen as a source of relatively efficient CCN, since the increase was significant only at high supersaturations.
Journal of Geophysical Research, 2007
1] The cloud-nucleating properties of the atmospheric aerosol were studied in an area under strong influence of vegetation burning. The measurements were part of Large-Scale Biosphere Atmosphere Experiment in Amazonia-Smoke Aerosols, Clouds, Rainfall and Climate (LBA-SMOCC) and were carried out at a ground site located in the state of Rondônia in southwestern Amazonia, Brazil, September to November 2002, covering the dry season, a transition period, and the onset of the wet season. The concentrations of cloud condensation nuclei (CCN) were measured with a static thermal gradient CCN counter for supersaturations ranging between 0.23 and 1.12%. As a closure test, the CCN concentrations were predicted with a time resolution of 10 min from measurements of the dry particle number size distribution (3-850 nm, Differential Mobility Analyzer (DMPS)) and hygroscopic growth at 90% relative humidity (Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA)). No chemical information was needed. The predicted and measured CCN concentrations were highly correlated (r 2 = 0.97-0.99), and the predictions were only slightly lower than those measured, typically by 15-20%. Parameterizations of the predicted CCN concentrations are given for each of the three meteorological periods. These are based on averages taken during the afternoon hours when the measurements at ground level were representative for the aerosol entering the base of convective clouds. Furthermore, a more detailed parameterization including the mixing state of the aerosol is given, where the hygroscopic properties are expressed as the number of soluble ions or nondissociating molecules per unit volume dry particle. Citation: Vestin, A., J. Rissler, E. Swietlicki, G. P. Frank, and M. O. Andreae (2007), Cloud-nucleating properties of the Amazonian biomass burning aerosol: Cloud condensation nuclei measurements and modeling,
Water uptake and chemical composition of fresh aerosols generated in open burning of biomass
Atmospheric Chemistry and Physics, 2010
As part of the Fire Lab at Missoula Experiments (FLAME) in 2006-2007, we examined hygroscopic properties of particles emitted from open combustion of 33 select biomass fuels. Measurements of humidification growth factors for subsaturated water relative humidity (RH) conditions were made with a hygroscopic tandem differential mobility analyzer (HTDMA) for dry particle sizes of 50, 100 and 250 nm. Results were then fit to a single-parameter model to obtain the hygroscopicity parameter, κ. Particles in freshly emitted biomass smoke exhibited a wide range of hygroscopicity (individual modes with 0 < κ < 1.0), spanning a range from the hygroscopicity of fresh diesel soot emissions to that of pure inorganic salts commonly found in the ambient aerosol. Smoke aerosols dominated by carbonaceous species typically had a unimodal growth factor with corresponding mean κ = 0.1 (range of 0 < κ < 0.4). Those with a substantial inorganic mass fraction typically separated into less-and more-hygroscopic modes at high RH, the latter with mean κ = 0.4 (range of 0.1 < κ < 1). The bimodal κ distributions were indicative of smoke chemical heterogeneity at a single particle size, whereas heterogeneity as a function of size was indicated by typically decreasing κ values with increasing dry particle diameters. Hygroscopicity varied strongly
Atmospheric Chemistry and Physics, 2010
During the 2006 FLAME study (Fire Laboratory at Missoula Experiment), laboratory burns of biomass fuels were performed to investigate the physico-chemical, optical, and hygroscopic properties of fresh biomass smoke. As part of the experiment, two nephelometers simultaneously measured dry and humidified light scattering co-5 efficients (b sp(dry) and b sp(RH) , respectively) in order to explore the role of relative humidity (RH) on the optical properties of biomass smoke aerosols. Results from burns of several biomass fuels showed large variability in the humidification factor (f (RH)=b sp(RH) /b sp(dry) ). Values of f (RH) at RH=85-90% ranged from 1.02 to 2.15 depending on fuel type. We incorporated measured chemical composition and size 10 distribution data to model the smoke hygroscopic growth to investigate the role of inorganic and organic compounds on water uptake for these aerosols. By assuming only inorganic constituents were hygroscopic, we were able to model the water uptake within experimental uncertainty, suggesting that inorganic species were responsible for most of the hygroscopic growth. In addition, humidification factors at 85-90% RH increased 15 for smoke with increasing inorganic salt to carbon ratios. Particle morphology as observed from scanning electron microscopy revealed that samples of hygroscopic particles contained soot chains either internally or externally mixed with inorganic potassium salts, while samples of weak to non-hygroscopic particles were dominated by soot and organic constituents. This study provides further understanding of the compounds re-20 sponsible for water uptake by young biomass smoke, and is important for accurately assessing the role of smoke in climate change studies and visibility regulatory efforts. Spracklen et al., 2007). Quantifying the role of biomass burning aerosols in climate 4227 ACPD 10, 4225-4269, 2010 Abstract Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion forcing and visibility degradation requires characterizing their optical, physical, chemical and hygroscopic properties. Many studies have been performed in the ambient atmosphere to measure radiative properties of smoke particles from wild fire and prescribed burning (see the review by Reid et al., 2005a, b). However, interpreting these results is complicated due to the variety of conditions under which the smoke was 5 ACPD 10, 4225-4269, 2010 Abstract Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion