The mesoscale HARMONIE model is used to investigate the potential influence of aerosols on weather forecasts, and in particular, on precipitation. The study considers three numerical experiments over the Atlantic-Euro...
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The mesoscale HARMONIE model is used to investigate the potential influence of aerosols on weather forecasts, and in particular, on precipitation. The study considers three numerical experiments over the Atlantic-Europe-Northern Africa region during 11-16 August 2010 with the following configurations: (a) no aerosols, (b) only the sea aerosols, and (c) the four types of the aerosols: sea, land, organic, and dust aerosols. The spatio-temporal analysis of forecast differences highlights the impact of aerosols on the prediction of main meteorological variables such as air temperature, humidity, precipitation, and cloud cover as well as their vertical profiles. The variations occur through changes in radiation fluxes and microphysics properties. The sensitivity experiments with the inclusion of climatological aerosol concentrations demonstrate the importance of aerosol effects on weather prediction. (C) 2015 Elsevier B.V. All rights reserved.
The region of the Indian Ocean and adjacent countries has received increased attention in recent years in the context of particulate air pollution. Aerosol samples were collected over the equatorial Indian Ocean durin...
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The region of the Indian Ocean and adjacent countries has received increased attention in recent years in the context of particulate air pollution. Aerosol samples were collected over the equatorial Indian Ocean during a one-year-long sailing cruise that covered the northeast and southwest monsoons, and an inter-monsoon period. The concentrations of airborne particulate matter (PM), selected metals and water-soluble ions were measured. In general, the PM concentrations were influenced by the proximity of sampling locations to land and air mass origins. The enrichment of metals in PM relative to those in the crustal material was very high (up to 40,000). The metal concentrations were significantly higher in PM samples which were influenced by volcanic emissions from the land masses of Indonesia. Volcanic plumes were traced using backward air mass trajectory and chemical tracers, and identified as a major particulate pollution source to the otherwise pristine air of the southern hemisphere of the Indian Ocean. NO3-, NH4+ and SO42- were low in aerosols collected over the open ocean, but a linear relationship between NH4+ and SO42- indicates their importance in the formation of cloud condensation nuclei. (C) 2011 Elsevier Ltd. All rights reserved.
Influence of pollution on dynamics of deep convection continues to be a controversial topic. Arguably, only carefully designed numerical simulations can clearly separate the impact of aerosols from the effects of mete...
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Influence of pollution on dynamics of deep convection continues to be a controversial topic. Arguably, only carefully designed numerical simulations can clearly separate the impact of aerosols from the effects of meteorological factors that affect moist convection. This paper argues that such a separation is virtually impossible using observations because of the insufficient accuracy of atmospheric measurements and the fundamental nature of the interaction between deep convection and its environment. To support this conjecture, results from numerical simulations are presented that apply modeling methodology previously developed by the author. The simulations consider small modifications, difficult to detect in observations, of the initial sounding, surface fluxes, and large-scale forcing tendencies. All these represent variations of meteorological conditions that affect deep convective dynamics independently of aerosols. The setup follows the case of daytime convective development over land based on observations during the Large-Scale Biosphere- Atmosphere (LBA) field project in Amazonia. The simulated observable macroscopic changes of convection, such as the surface precipitation and upper-tropospheric cloudiness, are similar to or larger than those resulting from changes of cloud condensation nuclei from pristine to polluted conditions studied previously using the same modeling case. Observations from Phase III of the Global Atmospheric Research Program Atlantic Tropical Experiment (GATE) are also used to support the argument concerning the impact of the large-scale forcing. The simulations suggest that the aerosol impacts on dynamics of deep convection cannot be isolated from meteorological effects, at least for the daytime development of unorganized deep convection considered in this study.
The chemical aging of liquid organic aerosols most likely occurs via exothermic heterogeneous chemical reactions on the aerosol's surface. Because of the enthalpy of reactions, the temperature of an aerosol partic...
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The chemical aging of liquid organic aerosols most likely occurs via exothermic heterogeneous chemical reactions on the aerosol's surface. Because of the enthalpy of reactions, the temperature of an aerosol particle during its chemical aging may become greater than the ambient (air) temperature. We attempt to shed light on this aspect of the formation of secondary organic aerosols considering their nucleation and chemical aging as concomitant processes. Using the model of aqueous hydrophilic-hydrophobic organic aerosols in the framework of classical nucleation theory, we evaluate characteristic time scales of the four most important processes involved in this complex phenomenon. Their analysis suggests that the release of the enthalpy of heterogeneous chemical reactions during the chemical aging of organic aerosols may play a significant impeding role in the formation of an ensemble of aqueous secondary organic aerosols via nucleation and hence must be taken into account in atmospheric aerosol and global climate models.
Atmospheric aerosols sampled in the Arctic Basin by impactors have been analyzed for total aerosol and its black carbon fraction. The mass of black carbon aerosol in the lower troposphere is 1% (1 g black carbon in 10...
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Atmospheric aerosols sampled in the Arctic Basin by impactors have been analyzed for total aerosol and its black carbon fraction. The mass of black carbon aerosol in the lower troposphere is 1% (1 g black carbon in 100 g total aerosol), reduced to one part in 10(4) in the stratosphere. The aerosol single scatter albedos vary between 1.0 in the stratosphere, currently dominated by high light scattering due to Pinatubo volcanic aerosol, and 0.94 in the lower troposphere. The aerosol has the potential to regionally warm the earth-atmosphere system because of the high surface albedo of snow-covered surfaces in the Arctic.
Vertical and temporal distributions of water-soluble, sea salt, and dust aerosols in the planetary boundary layer (PBL) were analyzed from two-wavelength (532 and 1064 nm) backscatter and one-wavelength (532 nm) polar...
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Vertical and temporal distributions of water-soluble, sea salt, and dust aerosols in the planetary boundary layer (PBL) were analyzed from two-wavelength (532 and 1064 nm) backscatter and one-wavelength (532 nm) polarization lidar measurements taken at Guangzhou in July 2006 and Beijing in August 2006. We used an algorithm that estimates the extinction coefficients for each aerosol component from the three-channel lidar data. The results revealed water-soluble aerosols, most of which were anthropogenic aerosols, were dominant in both cities. Air pollution events occurred on 12 and 22-24 July in Guangzhou and on 3-11, 16-19, and 23-25 August in Beijing. Differences in temporal variation of extinction coefficient of water-soluble particles (sigma(ws)) in the lower layers during the air pollution periods were distinct: sigma(ws) was higher in the nighttime at Beijing, whereas sigma(ws) was higher in the daytime in Guangzhou. Meanwhile similar vertical structures of sigma(ws) in the planetary boundary layer were found for both cities: sigma(ws) increased as the altitude increased. We suggest that different mechanisms contributed to the temporal and vertical variations of sigma(ws) in each city: hygroscopic growth mainly enhanced sigma(ws) in the nighttime and at high altitude for Beijing, while the transport of aerosols in the local area mainly enhanced sigma(ws) in the daytime and at high altitude in Guangzhou. Distinct differences were also observed in the sea-salt components in Guangzhou and in the dust components in Beijing. The correlation of the dust concentration and aerosol depolarization ratio implies that internal mixing of water-soluble and dust particles occurred in Beijing during the air pollution periods. (C) 2010 Elsevier B.V. All rights reserved.
The long-range transported smokes emitted by biomass burning had a strong impact on the PM2.5 mass concentrations in Helsinki over the 12 days period in April and May 2006. To characterize aerosols during this period,...
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The long-range transported smokes emitted by biomass burning had a strong impact on the PM2.5 mass concentrations in Helsinki over the 12 days period in April and May 2006. To characterize aerosols during this period, the real-time measurements were done for PM2.5, PM2.5-10, common ions and black carbon. Moreover, the 24-h PM1 filter samples were analysed for organic and elemental carbon (OC and EC), water-soluble organic carbon (WSOC), ions and levoglucosan. The Finnish emergency and air quality modelling system SILAM was used for the forecast of the PM2.5 concentration generated by biomass burning. According to the real-time PM2.5 data, the investigated period was divided into four types of PM situations: episode 1 (EPI-1;25-29 April), episode 2 (EPI-2;1-5 May), episode 3 (EPI-3;5-6 May) and a reference period (REF;24 March-24 April). EPI-3 included a local warehouse fire and therefore it is discussed separately. The PM I mass concentrations of biomass burning tracers-levoglucosan, potassium and oxalate-increased during the two long-range transport episodes (EPI-1 and EPI-2). The most substantial difference between the episodes was exhibited by the sulphate concentration, which was 4.9 (+/- 1.4) mu g m(-3) in EPI-2 but only 2.4 (+/- 0.31) mu g m(-3) in EPI-1 being close to that of REF (1.8 +/- 0.54 mu g m(-3)). The concentration of particulate organic matter in PM1 was clearly higher during EPI-1 (11 +/- 3.3 mu g m(-3)) and EPI-2 (9.7 +/- 4.0 mu g m(-3)) than REF (1.3 +/- 0.45 mu g m(-3)). The long-range transported smoke had only a minor impact on the WSOC-to-OC ratio. According to the model simulations, MODIS detected the fires that caused the first set of concentration peaks (EPI-1) and the local warehouse fire (EPI-3), but missed the second one (EPI-2) probably due to dense frontal clouds. (c) 2007 Elsevier Ltd. All rights reserved.
The aim of this work was to investigate ultrafine particles (<0.1 mu m) in primary school classrooms, in relation to the classroom activities. The investigations were conducted in three classrooms during two measur...
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The aim of this work was to investigate ultrafine particles (<0.1 mu m) in primary school classrooms, in relation to the classroom activities. The investigations were conducted in three classrooms during two measuring campaigns, which together encompassed a period of 60 days. Initial investigations showed that under the normal operating conditions of the school there were many occasions in all three classrooms where indoor particle concentrations increased significantly compared to outdoor levels. By far the highest increases in the classroom resulted from art activities (painting, gluing, and drawing), at times reaching over 1.4 x 10(5) particle cm(-3). The indoor particle concentrations exceeded outdoor concentrations by approximately 1 order of magnitude, with a count median diameter ranging from 20 to 50 nm. Significant increases also occurred during cleaning activities, when detergents were used. GC-MS analysis conducted on 4 samples randomly selected from about 30 different paints and glues, as well as the detergent used in the school, showed that d-limonene was one of the main organic compounds of the detergent, however, it was not detected in the samples of the paints and the glue. Controlled experiments showed that this monoterpene, emitted from the detergent, reacted with O-3 (at outdoor ambient concentrations ranging from 0.06 to 0.08 ppm) and formed secondary organic aerosols. Further investigations to identify other liquids that may be potential sources of the precursors of secondary organic aerosols were outside the scope of this project, however, it is expected that the problem identified by this study could be more widely spread, since most primary schools use liquid materials for art classes, and all schools use detergents for cleaning. Further studies are therefore recommended to better understand this phenomenon and also to minimize exposure of school children to ultrafine particles from these indoor sources.
Calcite (CaCO3) aerosols often serve as an idealized proxy for calcium-rich mineral dust. Their use has also previously been proposed for stratospheric solar radiation management (SSRM). Little is known about the hete...
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Calcite (CaCO3) aerosols often serve as an idealized proxy for calcium-rich mineral dust. Their use has also previously been proposed for stratospheric solar radiation management (SSRM). Little is known about the heterogeneous chemistry of calcite aerosols with trace gases HNO3 and HCl and therefore their potential impact on stratospheric ozone (O-3). Here we report the results of an experimental study of the uptake of HNO3 and HCl onto submicron CaCO3 particles in two different flow reactors. Products and reaction kinetics were observed by impacting aerosolized CaCO3 onto ZnSe windows, exposing them to the reagent gases at a wide range of concentrations, at 296 K and under dry conditions, and analyzing the particles before and after trace gas exposure using Fourier transform infrared spectroscopy (FTIR). A Ca(OH)(HCO3) termination layer was detected in the form of a HCO3- peak in the FTIR spectra, indicating a hydrated surface even under dry conditions. The results demonstrate the reaction of HNO3 with Ca(OH)(HCO3) to produce Ca(NO3)(2), water, and CO2. HCl reacted with Ca(OH)(HCO3) to produce CaCl2 and also water and CO2. The depletion of the Ca(OH)(HCO3)/Ca(CO3) signal due to reaction with HNO3 or HCl followed pseudo-first-order kinetics. From the FTIR analysis, the reactive uptake coefficient for HNO3 was determined to be in the range of 0.013 =.HNO3 = 0.14, and that for HCl was 0.0011 =.HCl = 0.012 within the reported uncertainty. The reaction of HCl with airborne CaCO3 aerosols was also studied in an aerosol flow tube coupled with a quadrupole chemical ionization mass spectrometer (CIMS) under similar conditions to the FTIR study, *** was determined to be 0.013 +/- 0.001. Following previous modeling studies, these results suggest that the reactions of HCl and HNO3 with calcite in the stratosphere could ameliorate the potential for stratospheric solar radiation management to lead to stratospheric ozone depletion.
Size-resolved aerosol samples, including the entire ultrafine fraction, were simultaneously collected along a transect in California's Central Valley during the winter of 2009. The samples were analyzed for PAHs, ...
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Size-resolved aerosol samples, including the entire ultrafine fraction, were simultaneously collected along a transect in California's Central Valley during the winter of 2009. The samples were analyzed for PAHs, alkanes, organic acids, and sugars. The results showed that the organic constituents of aerosols did not follow the same pattern as PM10, thus indicating that simple PM measurements are not good indicators of trace toxic organic chemicals. Levoglucosan, a tracer of wood smoke, was the most abundant organic chemical detected, thus demonstrating the predominance of wood smoke in the valley. The size profile of levoglucosan showed a maximum in the 0.34-0.56 mu m size mode, which is larger than published emission profiles. This suggests that wood smoke aerosols increased in size as they aged in the environment. Some chemicals, such as benzo[a]pyrene, had similar aerosol size profiles as levoglucosan and likely arose from the same source. Other chemicals, such as coronene and sugars, had very different size profiles, indicating that they have different sources. One unexpected result was the relatively large fraction of certain chemicals present in the ultrafine fraction, which highlights the importance of collecting the entire ultrafine fraction.
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