A large part of the uncertainty in climate projections comes from uncertain aerosol properties and aerosol–cloud interactions as well as the difficulty in remotely sensing them. The southeastern ...Atlantic functions as a natural laboratory to study biomass-burning smoke and to constrain this uncertainty. We address these gaps by comparing the Weather Research and Forecasting with Chemistry Community Atmosphere Model (WRF-CAM5) to the multi-campaign observations ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS), CLARIFY (CLoud–Aerosol–Radiation Interaction and Forcing), and LASIC (Layered Atlantic Smoke Interactions with Clouds) in the southeastern Atlantic in August 2017 to evaluate a large range of the model's aerosol chemical properties, size distributions, processes, and transport, as well as aerosol–cloud interactions. Overall, while WRF-CAM5 is able to represent smoke properties and transport, some key discrepancies highlight the need for further analysis. Observations of smoke composition show an overall decrease in aerosol mean diameter as smoke ages over 4–12 d, while the model lacks this trend. A decrease in the mass ratio of organic aerosol (OA) to black carbon (BC), OA:BC, and the OA mass to carbon monoxide (CO) mixing ratio, OA:CO, suggests that the model is missing processes that selectively remove OA from the particle phase, such as photolysis and heterogeneous aerosol chemistry. A large (factor of ∼2.5) enhancement in sulfate from the free troposphere (FT) to the boundary layer (BL) in observations is not present in the model, pointing to the importance of properly representing secondary sulfate aerosol formation from marine dimethyl sulfide and gaseous SO2 smoke emissions. The model shows a persistent overprediction of aerosols in the marine boundary layer (MBL), especially for clean conditions, which multiple pieces of evidence link to weaker aerosol removal in the modeled MBL than reality. This evidence includes several model features, such as not representing observed shifts towards smaller aerosol diameters, inaccurate concentration ratios of carbon monoxide and black carbon, underprediction of heavy rain events, and little evidence of persistent biases in modeled entrainment. The average below-cloud aerosol activation fraction (NCLD/NAER) remains relatively constant in WRF-CAM5 between field campaigns (∼0.65), while it decreases substantially in observations from ORACLES (∼0.78) to CLARIFY (∼0.5), which could be due to the model misrepresentation of clean aerosol conditions. WRF-CAM5 also overshoots an observed upper limit on liquid cloud droplet concentration around NCLD= 400–500 cm−3 and overpredicts the spread in NCLD. This could be related to the model often drastically overestimating the strength of boundary layer vertical turbulence by up to a factor of 10. We expect these results to motivate similar evaluations of other modeling systems and promote model development to reduce critical uncertainties in climate simulations.
Aerosols in the Pre-industrial Atmosphere Carslaw, Kenneth S.; Gordon, Hamish; Hamilton, Douglas S. ...
Current climate change reports,
03/2017, Volume:
3, Issue:
1
Journal Article
Peer reviewed
Open access
Purpose of Review
We assess the current understanding of the state and behaviour of aerosols under pre-industrial conditions and the importance for climate.
Recent Findings
Studies show that the ...magnitude of anthropogenic aerosol radiative forcing over the industrial period calculated by climate models is strongly affected by the abundance and properties of aerosols in the pre-industrial atmosphere. The low concentration of aerosol particles under relatively pristine conditions means that global mean cloud albedo may have been twice as sensitive to changes in natural aerosol emissions under pre-industrial conditions compared to present-day conditions. Consequently, the discovery of new aerosol formation processes and revisions to aerosol emissions have large effects on simulated historical aerosol radiative forcing.
Summary
We review what is known about the microphysical, chemical, and radiative properties of aerosols in the pre-industrial atmosphere and the processes that control them. Aerosol properties were controlled by a combination of natural emissions, modification of the natural emissions by human activities such as land-use change, and anthropogenic emissions from biofuel combustion and early industrial processes. Although aerosol concentrations were lower in the pre-industrial atmosphere than today, model simulations show that relatively high aerosol concentrations could have been maintained over continental regions due to biogenically controlled new particle formation and wildfires. Despite the importance of pre-industrial aerosols for historical climate change, the relevant processes and emissions are given relatively little consideration in climate models, and there have been very few attempts to evaluate them. Consequently, we have very low confidence in the ability of models to simulate the aerosol conditions that form the baseline for historical climate simulations. Nevertheless, it is clear that the 1850s should be regarded as an early industrial reference period, and the aerosol forcing calculated from this period is smaller than the forcing since 1750. Improvements in historical reconstructions of natural and early anthropogenic emissions, exploitation of new Earth system models, and a deeper understanding and evaluation of the controlling processes are key aspects to reducing uncertainties in future.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The “Campaign on Atmospheric Aerosol Research” network of China (CARE-China) is a long-term project for the study of the spatio-temporal distributions of physical aerosol characteristics as well as ...the chemical components and optical properties of aerosols over China. This study presents the first long-term data sets from this project, including 3 years of observations of online PM2.5 mass concentrations (2012–2014) and 1 year of observations of PM2.5 compositions (2012–2013) from the CARE-China network. The average PM2.5 concentration at 20 urban sites is 73.2 µg m−3 (16.8–126.9 µg m−3), which was 3 times higher than the average value from the 12 background sites (11.2–46.5 µg m−3). The PM2.5 concentrations are generally higher in east-central China than in the other parts of the country due to their relatively large particulate matter (PM) emissions and the unfavourable meteorological conditions for pollution dispersion. A distinct seasonal variability in PM2.5 is observed, with highs in the winter and lows during the summer at urban sites. Inconsistent seasonal trends were observed at the background sites. Bimodal and unimodal diurnal variation patterns were identified at both urban and background sites. The chemical compositions of PM2.5 were analysed at six paired urban and background sites located within the most polluted urban agglomerations – North China Plain (NCP), Yangtze River delta (YRD), Pearl River delta (PRD), North-east China region (NECR), South-west China region (SWCR) – and the cleanest region of China – the Tibetan Autonomous Region (TAR). The major PM2.5 constituents across all the urban sites are organic matter (OM, 26.0 %), SO42- (17.7 %), mineral dust (11.8 %), NO3- (9.8 %), NH4+ (6.6 %), elemental carbon (EC) (6.0 %), Cl− (1.2 %) at 45 % RH and unaccounted matter (20.7 %). Similar chemical compositions of PM2.5 were observed at background sites but were associated with higher fractions of OM (33.2 %) and lower fractions of NO3- (8.6 %) and EC (4.1 %). Significant variations of the chemical species were observed among the sites. At the urban sites, the OM ranged from 12.6 µg m−3 (Lhasa) to 23.3 µg m−3 (Shenyang), the SO42- ranged from 0.8 µg m−3 (Lhasa) to 19.7 µg m−3 (Chongqing), the NO3- ranged from 0.5 µg m−3 (Lhasa) to 11.9 µg m−3 (Shanghai) and the EC ranged from 1.4 µg m−3 (Lhasa) to 7.1 µg m−3 (Guangzhou). The PM2.5 chemical species at the background sites exhibited larger spatial heterogeneities than those at urban sites, suggesting different contributions from regional anthropogenic or natural emissions and from long-range transport to background areas. Notable seasonal variations of PM2.5-polluted days were observed, especially for the megacities in east-central China, resulting in frequent heavy pollution episodes occurring during the winter. The evolution of the PM2.5 chemical compositions on polluted days was consistent for the urban and nearby background sites, where the sum of sulfate, nitrate and ammonia typically constituted much higher fractions (31–57 %) of PM2.5 mass, suggesting fine-particle pollution in the most polluted areas of China assumes a regional tendency, and the importance of addressing the emission reduction of secondary aerosol precursors including SO2 and NOx. Furthermore, distinct differences in the evolution of NO3-/SO42- ratio and OC∕EC ratio on polluted days imply that mobile sources and stationary (coal combustion) sources are likely more important in Guangzhou and Shenyang, respectively, whereas in Beijing it is mobile emission and residential sources. As for Chongqing, the higher oxidation capacity than the other three cities suggested it should pay more attention to the emission reduction of secondary aerosol precursors. This analysis reveals the spatial and seasonal variabilities of the urban and background aerosol concentrations on a national scale and provides insights into their sources, processes and lifetimes.
One-pot aerosol-assisted synthesis of mesostructured (Co)Mo/SiO sub(2) catalysts with high hydrogenation activity is reported. The evaporation*induced self-assembly mechanism of the formation of such ...catalysts enables optimized interactions between each component, resulting in the tuning of localization of the active species. The high activity is probably associated with the original morphology of the active phase as well as the creation of relevant defects in its structure. Since spray-dried mesoporous CoMo/SiO sub(2) catalysts outperform the hydrogenation activity of classical impregnated catalysts, aerosol route appears to be a promising way for the industrial-scale preparation of new highly efficient hydrocarbons catalysts. One-pot synthesis through spray drying of large structured porous (Co)Mo/SiO sub(2) composite presenting high hydrogenating activity is reported. This high activity is associated with both a tuned localization of the active species inside the mesopores and to the formation of nanoscopic molybdenum sulfide entangled slabs that likely promote the number of catalytically relevant defects.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Observations show that the concentrations of Arctic sulfate and black carbon
(BC) aerosols have declined since the early 1980s. Previous studies have
reported that reducing sulfate aerosols ...potentially contributed to the
recent rapid Arctic warming. In this study, a global aerosol–climate model (Community Atmosphere
Model, version 5) equipped with Explicit Aerosol Source Tagging (CAM5-EAST) is applied to
quantify the source apportionment of aerosols in the Arctic from 16
source regions and the role of aerosol variations in affecting changes in
the Arctic surface temperature from 1980 to 2018. The CAM5-EAST simulated
surface concentrations of sulfate and BC in the Arctic had a decrease of
43 % and 23 %, respectively, in 2014–2018 relative to 1980–1984
mainly due to the reduction of emissions from Europe, Russia and local Arctic sources. Increases in emissions from South and East Asia led to
positive trends in Arctic sulfate and BC in the upper troposphere. All
aerosol radiative impacts are considered including aerosol–radiation and
aerosol–cloud interactions, as well as black carbon deposition on snow- and
ice-covered surfaces. Within the Arctic, sulfate reductions caused a
top-of-atmosphere (TOA) warming of 0.11 and 0.25 W m−2
through aerosol–radiation and aerosol–cloud interactions, respectively.
While the changes in Arctic atmospheric BC has little impact on local
radiative forcing, the decrease in BC in snow and ice led to a net cooling of
0.05 W m−2. By applying climate sensitivity factors for different
latitudinal bands, global changes in sulfate and BC during 2014–2018 (with
respect to 1980–1984) exerted a +0.088 and 0.057 K Arctic surface
warming, respectively, through aerosol–radiation interactions. Through
aerosol–cloud interactions, the sulfate reduction caused an Arctic warming of
+0.193 K between the two time periods. The weakened BC effect on snow–ice
albedo led to an Arctic surface cooling of −0.041 K. The changes in
atmospheric sulfate and BC outside the Arctic produced a total Arctic
warming of +0.25 K, the majority of which is due to the midlatitude
changes in radiative forcing. Our results suggest that changes in aerosols
over the midlatitudes of the Northern Hemisphere have a larger impact on
Arctic temperature than other regions through enhanced poleward heat
transport. The combined total effects of sulfate and BC produced an Arctic
surface warming of +0.297 K, explaining approximately 20 % of the
observed Arctic warming since the early 1980s.
Objective
In the era of SARS-CoV-2, the risk of infectious airborne aerosol generation during otolaryngologic procedures has been an area of increasing concern. The objective of this investigation ...was to quantify airborne aerosol production under clinical and surgical conditions and examine efficacy of mask mitigation strategies.
Study Design
Prospective quantification of airborne aerosol generation during surgical and clinical simulation.
Setting
Cadaver laboratory and clinical examination room.
Subjects and Methods
Airborne aerosol quantification with an optical particle sizer was performed in real time during cadaveric simulated endoscopic surgical conditions, including hand instrumentation, microdebrider use, high-speed drilling, and cautery. Aerosol sampling was additionally performed in simulated clinical and diagnostic settings. All clinical and surgical procedures were evaluated for propensity for significant airborne aerosol generation.
Results
Hand instrumentation and microdebridement did not produce detectable airborne aerosols in the range of 1 to 10 μm. Suction drilling at 12,000 rpm, high-speed drilling (4-mm diamond or cutting burs) at 70,000 rpm, and transnasal cautery generated significant airborne aerosols (P < .001). In clinical simulations, nasal endoscopy (P < .05), speech (P < .01), and sneezing (P < .01) generated 1- to 10-μm airborne aerosols. Significant aerosol escape was seen even with utilization of a standard surgical mask (P < .05). Intact and VENT-modified (valved endoscopy of the nose and throat) N95 respirator use prevented significant airborne aerosol spread.
Conclusion
Transnasal drill and cautery use is associated with significant airborne particulate matter production in the range of 1 to 10 μm under surgical conditions. During simulated clinical activity, airborne aerosol generation was seen during nasal endoscopy, speech, and sneezing. Intact or VENT-modified N95 respirators mitigated airborne aerosol transmission, while standard surgical masks did not.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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