We performed airborne measurements of atmospheric trace gases and aerosol composition on the NCAR C-130 research aircraft over the tropical Indian Ocean during the Indian Ocean Experiment (INDOEX) ...intensive field phase in February and March 1999. Gases measured included acetone, acetonitrile, sulfur dioxide, and carbon monoxide. The aerosol composition was analyzed for water-soluble ions, and black and organic carbon. South of the ITCZ, we sampled pristine air originating from the remote southern Indian Ocean. North of the ITCZ, signatures of heavy pollution were evident over large areas of the Indian Ocean. Heavy pollution was present in the marine boundary layer as well as in the free troposphere at altitudes up to almost 4000 m. Outflow from the Indian subcontinent as well as from other source regions (Arabian Sea, Southeast Asia) could be identified by back trajectory calculations using the Hybrid Single Particle Lagrangian Integrated Trajectory model. The highest pollutant concentrations were observed in a free tropospheric pollution layer ("residual layer"), which originated from the Indian continental boundary layer. High mixing ratios of acetonitrile (up to 0.8 ppb) and submicron aerosol potassium (up to 0.6 ppb) indicate an important contribution from biomass or biofuel burning sources. On the other hand, high mixing ratios of sulfur dioxide (up to 1.5 ppb) and aerosol sulfate (up to 3 ppb) indicate the influence of fossil fuel burning. (Author)
Atmospheric aerosol particles serving as cloud condensation nuclei (CCN) are key elements of the hydrological cycle and climate. We have measured and characterized CCN at water vapor supersaturations ...in the range of S=0.10-0.82% in pristine tropical rainforest air during the AMAZE-08 campaign in central Amazonia. The effective hygroscopicity parameters describing the influence of chemical composition on the CCN activity of aerosol particles varied in the range of Kappa =0.05-0.45. The overall median value of Kappa ≈ 0.15 was only half of the value typically observed for continental aerosols in other regions of the world. Aitken mode particles were less hygroscopic than accumulation mode particles ( Kappa ≈ 0.1 at D≈ 50 nm; Kappa ≈ 0.2 at D≈ 200 nm). The CCN measurement results were fully consistent with aerosol mass spectrometry (AMS) data, which showed that the organic mass fraction (X sub(m,org)) was on average as high as ~90% in the Aitken mode (D less than or equal to 100 nm) and decreased with increasing particle diameter in the accumulation mode (~80% at D≈ 200 nm). The Kappa values exhibited a close linear correlation with X sub(m,org) and extrapolation yielded the following effective hygroscopicity parameters for organic and inorganic particle components: Kappa sub(org)≈ 0.1 which is consistent with laboratory measurements of secondary organic aerosols and Kappa sub(inorg)≈ 0.6 which is characteristic for ammonium sulfate and related salts. Both the size-dependence and the temporal variability of effective particle hygroscopicity could be parameterized as a function of AMS-based organic and inorganic mass fractions ( Kappa sub(p)=0.1 X sub(m,org)+0.6 X sub(m,inorg)), and the CCN number concentrations predicted with Kappa sub(p) were in fair agreement with the measurement results. The median CCN number concentrations at S=0.1-0.82% ranged from N sub(CCN,0.10)≈ 30 cm super(− 3) to N sub(CCN,0.82)≈ 150 cm super(− 3), the median concentration of aerosol particles larger than 30 nm was N sub(CN,30)≈ 180 cm super(− 3), and the corresponding integral CCN efficiencies were in the range of N sub(CCN,0.10)/N sub(CN,30)� 26; asymp; 0.1 to N sub(CCN,0.82)/N sub(CN,30)� 26; asymp; 0.8. Although the number concentrations and hygroscopicity parameters were much lower, the integral CCN efficiencies observed in pristine rainforest air were similar to those in highly polluted mega-city air. Moreover, model calculations of N sub(CCN,S) with a global average value of Kappa =0.3 led to systematic overpredictions, but the relative deviations exceeded ~50% only at low water vapor supersaturation (0.1%) and low particle number concentrations ( less than or equal to 100 cm super(− 3)). These findings confirm earlier studies suggesting that aerosol particle number and size are the major predictors for the variability of the CCN concentration in continental boundary layer air, followed by particle composition and hygroscopicity as relatively minor modulators. Depending on the required and applicable level of detail, the information and parameterizations presented in this paper should enable efficient description of the CCN properties of pristine tropical rainforest aerosols in detailed process models as well as in large-scale atmospheric and climate models.
During the 1st Lagrangian experiment of the North Atlantic Regional Aerosol Characterisation Experiment (ACE-2), a parcel of air was tagged by releasing a smart, constant level balloon into it from ...the Research Vessel Vodyanitskiy. The Meteorological Research Flight's C-130 aircraft then followed this parcel over a period of 30 h characterising the marine boundary layer (MBL), the cloud and the physical and chemical aerosol evolution. The air mass had originated over the northern North Atlantic and thus was clean and had low aerosol concentrations. At the beginning of the experiment the MBL was over 1500 m deep and made up of a surface mixed layer (SML) underlying a layer containing cloud beneath a subsidence inversion. Subsidence in the free troposphere caused the depth of the MBL to almost halve during the experiment and, after 26 h, the MBL became well mixed throughout its whole depth. Salt particle mass in the MBL increased as the surface wind speed increased from 8 m s
-1
to 16 m s
-1
and the accumulation mode (0.1μm to 3.0 μm) aerosol concentrations quadrupled from 50 cm
-3
to 200 cm
-3
. However, at the same time the total condensation nuclei (>3 nm) decreased from over 1000 cm
-3
to 750 cm
-3
. The changes in the accumulation mode aerosol concentrations had a significant effect on the observed cloud microphysics. Observational evidence suggests that the important processes in controlling the Aitken mode concentration which, dominated the total CN concentration, included, scavenging of interstitial aerosol by cloud droplets, enhanced coagulation of Aitken mode aerosol and accumulation mode aerosol due to the increased sea salt aerosol surface area, and dilution of the MBL by free tropospheric air.
New particle formation (NPF) in fire smoke is thought to be unlikely due to large condensation and coagulation sinks that scavenge molecular clusters. We analyze aircraft measurements over the Amazon ...and find that fires significantly enhance NPF and ultrafine particle (UFP < 50 nm diameter) numbers compared to background conditions, contrary to previous understanding. We identify that the nucleation of dimethylamine with sulfuric acid, which is aided by the formation of extremely low volatility organics in biomass-burning smoke, can overcome the large condensation and coagulation sinks and explain aircraft observations. We show that freshly formed clusters rapidly grow to UFP sizes through biomass-burning secondary organic aerosol formation, leading to a 10-fold increase in UFP number concentrations. We find a contrasting effect of UFPs on deep convective clouds compared to the larger particles from primary emissions for the case investigated here. UFPs intensify the deep convective clouds and precipitation due to increased condensational heating, while larger particles delay and reduce precipitation.
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•Aircraft measurements in vegetation fires show abundant ultrafine particles (UFPs)•Previous model formulations greatly underpredict the observed fire UFPs•Nucleation of dimethylamines from fires with sulfuric acid explains observed UFPs•UFPs from fires intensify deep convective clouds and precipitation
Fine particles in wildfire smoke can lower air quality and harm human health. Smoke can also influence weather and climate by modifying cloud formation and changing how much of the sun’s energy is reflected or absorbed by the atmosphere. Compared to larger particles directly emitted from fires, the formation and presence of ultrafine particles (UFPs) have previously been overlooked, as it was thought that they were quickly “scavenged” by the larger particles. However, we found that UFPs were abundant in aircraft measurements of smoke from vegetation fires in the Amazon, and their formation and survival were favored. Furthermore, high-resolution modeling showed that these UFPs may intensify cloud convection and heavy rain. This research deepens our understanding of how vegetation fires impact weather and climate change.
Ultrafine particles (UFPs) in biomass-burning smoke are formed by efficient nucleation mechanisms, including dimethylamines and sulfuric acid, and nucleated clusters grow by the condensation of oxidized organic vapors. UFPs may cause a stronger storm with a larger anvil and heavier rain, while larger particles directly emitted by fires delay and suppress rain.
Every year, from December to April, anthropogenic haze spreads over most of the North Indian Ocean, and South and Southeast Asia. The Indian Ocean Experiment (INDOEX) documented this Indo-Asian haze ...at scales ranging from individual particles to its contribution to the regional climate forcing. This study integrates the multiplatform observations (satellites, aircraft, ships, surface stations, and balloons) with 1D and 4D models to derive the regional aerosol forcing resulting from the direct, the semidirect, and the two indirect effects. The haze particles consisted of several inorganic and carbonaceous species, including absorbing black carbon clusters, fly ash, and mineral dust. The most striking result was the large loading of aerosols over most of the South Asian region and the North Indian Ocean. The January to March 1999 visible optical depths were about 0.5 over most of the continent and reached values as large as 0.2 over the equatorial Indian ocean due to long-range transport. The aerosol layer extended as high as 3 km. Black carbon contributed about 14 percent to the fine particle mass and 11 percent to the visible optical depth. The single-scattering albedo estimated by several independent methods was consistently around 0.9 both inland and over the open ocean. Anthropogenic sources contributed as much as 80 percent (+/- 10 percent) to the aerosol loading and the optical depth. (Author)
We investigated smoke emissions from fires in savanna, forest, and agricultural ecosystems by airborne sampling of plumes close to prescribed burns and incidental fires in southern Africa. Aerosol ...samples were collected on glass fiber filters and on stacked filter units, consisting of a Nuclepore prefilter for particles larger than approximately 1-2 microns and a Teflon second-filter stage for the submicron fraction. The samples were analyzed for soluble ionic components, organic carbon, and black carbon. Onboard the research aircraft, particle number and volume distributions as a function of size were determined with a laser-optical particle counter and the black carbon content of the aerosol with an aethalometer. We determined the emission ratios (relative to CO2 and CO) and emission factors (relative to the amount of biomass burnt) for the various aerosol constituents. The smoke aerosols were rich in organic and black carbon, the latter representing 10-30 percent of the aerosol mass. K(+) and NH4(+) were the dominant cationic species in the smoke of most fires, while Cl(-) and SO4(2-) were the most important anions. The aerosols were unusually rich in Cl(-), probably due to the high Cl content of the semiarid vegetation. (Author)
During the Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) campaign, size-resolved cloud condensation nuclei (CCN) spectra were characterized at a research site (T3) 60 km ...downwind of the city of Manaus, Brazil, in central Amazonia for 1 year (12 March 2014 to 3 March 2015). Particle hygroscopicity (κCCN) and mixing state were derived from the size-resolved CCN spectra, and the hygroscopicity of the organic component of the aerosol (κorg) was then calculated from κCCN and concurrent chemical composition measurements. The annual average κCCN increased from 0.13 at 75 nm to 0.17 at 171 nm, and the increase was largely due to an increase in sulfate volume fraction. During both wet and dry seasons, κCCN, κorg, and particle composition under background conditions exhibited essentially no diel variations. The constant κorg of ∼ 0. 15 is consistent with the largely uniform and high O : C value (∼ 0. 8), indicating that the aerosols under background conditions are dominated by the aged regional aerosol particles consisting of highly oxygenated organic compounds. For air masses strongly influenced by urban pollution and/or local biomass burning, lower values of κorg and organic O : C atomic ratio were observed during night, due to accumulation of freshly emitted particles, dominated by primary organic aerosol (POA) with low hygroscopicity, within a shallow nocturnal boundary layer. The O : C, κorg, and κCCN increased from the early morning hours and peaked around noon, driven by the formation and aging of secondary organic aerosol (SOA) and dilution of POA emissions into a deeper boundary layer, while the development of the boundary layer, which leads to mixing with aged particles from the residual layer aloft, likely also contributed to the increases. The hygroscopicities associated with individual organic factors, derived from PMF (positive matrix factorization) analysis of AMS (aerosol mass spectrometry) spectra, were estimated through multivariable linear regression. For the SOA factors, the variation of the κ value with O : C agrees well with the linear relationship reported from earlier laboratory studies of SOA hygroscopicity. On the other hand, the variation in O : C of ambient aerosol organics is largely driven by the variation in the volume fractions of POA and SOA factors, which have very different O : C values. As POA factors have hygroscopicity values well below the linear relationship between SOA hygroscopicity and O : C, mixtures with different POA and SOA fractions exhibit a steeper slope for the increase in κorg with O : C, as observed during this and earlier field studies. This finding helps better understand and reconcile the differences in the relationships between κorg and O : C observed in laboratory and field studies, therefore providing a basis for improved parameterization in global models, especially in a tropical context.
We investigated smoke emissions from fires in savanna, forest, and agricultural ecosystems by airborne sampling of plumes close to prescribed burns and incidental fires in southern Africa. Aerosol ...samples were collected on glass fiber filters and on stacked filter units, consisting of a Nuclepore prefilter for particles larger than similar to 1-2 mu m and a Teflon second filter stage for the submicron fraction. The samples were analyzed for soluble ionic components, organic carbon, and black carbon. Onboard the research aircraft, particle number and volume distributions as a function of size were determined with a laser-optical particle counter and the black carbon content of the aerosol with an aethalometer. We determined the emission ratios (relative to CO sub(2) and CO) and emission factors (relative to the amount of biomass burnt) for the various aerosol constituents. The smoke aerosols were rich in organic and black carbon, the latter representing 10-30% of the aerosol mass. K super(+) and NH sub(4) super(+) were the dominant cationic species in the smoke of most fires, while Cl super(-) and SO sub(4) super(2-) were the most important anions. The aerosols were unusually rich in Cl super(-), probably due to the high Cl content of the semiarid vegetation. Comparison of the element budget of the fuel before and after the fires shows that the fraction of the elements released during combustion is highly variable between elements. In the case of the halogen elements, almost the entire amount released during the fire is present in the aerosol phase, while in the case of C, N, and S, only a small proportion ends up as particulate matter. This suggests that the latter elements are present predominantly as gaseous species in the fresh fire plumes studied here.
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