Atmosphere

5014 KiB

Open AccessArticle

An Assessment of the South Asian Summer Monsoon Variability for Present and Future Climatologies Using a High Resolution Regional Climate Model (RegCM4.3) under the AR5 Scenarios

by Mujtaba Hassan, Pengfei Du, Shaofeng Jia, Waheed Iqbal, Rashid Mahmood and Wulong Ba

Atmosphere 2015, 6(11), 1833-1857; https://doi.org/10.3390/atmos6111833 - 23 Nov 2015

Cited by 26 | Viewed by 8257

Abstract

We assessed the present and future climatologies of mean summer monsoon over South Asia using a high resolution regional climate model (RegCM4) with a 25 km horizontal resolution. In order to evaluate the performance of the RegCM4 for the reference period (1976–2005) and [...] Read more.

We assessed the present and future climatologies of mean summer monsoon over South Asia using a high resolution regional climate model (RegCM4) with a 25 km horizontal resolution. In order to evaluate the performance of the RegCM4 for the reference period (1976–2005) and for the far future (2070–2099), climate change projections under two greenhouse gas representative concentration pathways (RCP4.5 and RCP8.5) were made, the lateral boundary conditions being provided by the geophysical fluid dynamic laboratory global model (GFDL-ESM2M). The regional climate model (RCM) improves the simulation of seasonal mean temperature and precipitation patterns compared to driving global climate model (GCM) during present-day climate conditions. The regional characteristic features of South Asian summer monsoon (SASM), like the low level jet stream and westerly flow over the northern the Arabian Sea, are well captured by the RegCM4. In spite of some discrepancies, the RegCM4 could simulate the Tibetan anticyclone and the direction of the tropical easterly jet reasonably well at 200 hPa. The projected temperature changes in 2070–2099 relative to 1976–2005 for GFDL-ESM2M show increased warming compared to RegCM4. The projected patterns at the end of 21st century shows an increase in precipitation over the Indian Peninsula and the Western Ghats. The possibilities of excessive precipitation include increased southwesterly flow in the wet period and the effect of model bias on climate change. However, the spatial patterns of precipitation are decreased in intensity and magnitude as the monsoon approaches the foothills of the Himalayas. The RegCM4-projected dry conditions over northeastern India are possibly related to the anomalous anticyclonic circulations in both scenarios. Full article

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2500 KiB

Open AccessArticle

Investigations of the Diurnal Variation of Vertical HCHO Profiles Based on MAX-DOAS Measurements in Beijing: Comparisons with OMI Vertical Column Data

by Hanlim Lee, Jaeyong Ryu, Hitoshi Irie, Seong-Ho Jang, Junsung Park, Wonei Choi and Hyunkee Hong

Atmosphere 2015, 6(11), 1816-1832; https://doi.org/10.3390/atmos6111816 - 20 Nov 2015

Cited by 18 | Viewed by 5502

Abstract

An investigation into the diurnal characteristics of vertical formaldehyde (HCHO) profiles was conducted based on multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements in Beijing during the CAREBEIJING campaign, covering a month-long period through August and September 2006. Vertical HCHO profiles were retrieved based [...] Read more.

An investigation into the diurnal characteristics of vertical formaldehyde (HCHO) profiles was conducted based on multi-axis differential optical absorption spectroscopy (MAX-DOAS) measurements in Beijing during the CAREBEIJING campaign, covering a month-long period through August and September 2006. Vertical HCHO profiles were retrieved based on a combined differential optical absorption spectroscopy (DOAS) technique and an optimal estimation method (OEM). The HCHO volume-mixing ratio (VMR) was found to be highest in the layer from the surface up to an altitude of 1 km and to decrease with altitude above this layer. In all retrieved profiles, HCHO was not detected in the layer from 3–4 km. Over the diurnal cycle, the HCHO VMR values were generally highest at 15:00 local time (LT) and were lower in the morning and late afternoon. The mean HCHO VMRs were 6.17, 1.82, and 0.80 ppbv for the 0–1, 1–2, and 2–3-km layers, respectively, at 15:00 LT, whereas they were 3.54 (4.79), 1.06 (1.43), and 0.46 (0.63) ppbv for the 0–1, 1–2, and 2–3-km layers, respectively, at 09:00 (17:00) LT. The HCHO VMRs reached their highest values at 15:00 LT on August 19, which were 17.71, 5.20, and 2.31 ppbv for the 0–1, 1–2, and 2–3-km layers, respectively. This diurnal pattern implies that the photo-oxidation of volatile organic compounds (VOCs) was most active at 15:00 LT for several days during the campaign period. In a comparison of the derived HCHO VCDs with those obtained from the Ozone Monitoring Instrument (OMI) measurements, the HCHO vertical column density (VCD) values obtained from the OMI measurements tend to be smaller than those from the MAX-DOAS. Full article

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896 KiB

Open AccessArticle

PM_2.5 Concentration Differences between Various Forest Types and Its Correlation with Forest Structure

by Xuhui Liu, Xinxiao Yu and Zhenming Zhang

Atmosphere 2015, 6(11), 1801-1815; https://doi.org/10.3390/atmos6111801 - 20 Nov 2015

Cited by 68 | Viewed by 7087

Abstract

The Plain Forestation Project is an important measure designed to alleviate air pollution in Beijing, the capital of China. Ten commonly cultivated forest types of the Plain Forestation Project were studied at three growth stages of leaves. The particulate matter (PM)_2.5 concentrations [...] Read more.

The Plain Forestation Project is an important measure designed to alleviate air pollution in Beijing, the capital of China. Ten commonly cultivated forest types of the Plain Forestation Project were studied at three growth stages of leaves. The particulate matter (PM)_2.5 concentrations and forest structures were surveyed to analyze the PM_2.5 concentration differences between different forest types, and establish a linear relationship between forest structures and PM_2.5 concentration differences. The results suggested that forest ecosystems can block and capture PM_2.5 from the air. Forests with luxuriant foliage are most effective in removing PM_2.5 from the air. The average PM_2.5 mass concentration in the Leaf-on Period (LOP) was the lowest when compared with other periods. The PM_2.5 concentrations in the forest usually were higher than the control. Correspondingly, PM_2.5 concentration indexes were negative values during daytime, but this results were reversed at night. Forests can reduce the diffusion rate of PM_2.5 leading to PM_2.5 were detained in the forest during daytime, and play an important role in the adsorption or deposition of particulate matter at night. Forest structure was primary reason of the PM_2.5 concentration difference between different forests. The PM_2.5 concentration index was positively correlated to canopy density, leaf area index (LAI), and mean diameter at breast height (DBH), and negatively correlated to the average tree height (height), forestland area, grass coverage and height. Full article

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1189 KiB

Open AccessArticle

pH Control in Fog and Rain in East Asia: Temporal Advection of Clean Air Masses to Mt. Bamboo, Taiwan

by Otto Klemm, Wei-Ti Tseng, Chia-Ching Lin, Kerstin I. Klemm and Neng-Huei (George) Lin

Atmosphere 2015, 6(11), 1785-1800; https://doi.org/10.3390/atmos6111785 - 20 Nov 2015

Cited by 5 | Viewed by 5487

Abstract

Fog and rain was collected during an 18-day period in January 2011 at Mt. Bamboo, northern Taiwan. Almost 300 hourly fog samples and 16 daily rain samples were taken. One single fog sample (pH 3.17) was influenced by local volcanic activity, otherwise the [...] Read more.

Fog and rain was collected during an 18-day period in January 2011 at Mt. Bamboo, northern Taiwan. Almost 300 hourly fog samples and 16 daily rain samples were taken. One single fog sample (pH 3.17) was influenced by local volcanic activity, otherwise the pH ranged from 3.23 to 6.41 in fog and from 3.59 to 6.31 in rain. All the respective air masses arrived from the northeast, but exhibited two distinct groups: Group_1 had high concentrations of all ions (median interquartile range of total ion concentrations 3200–6200 µeq.·L⁻¹) and low pHs (median 3.52), the respective air masses had travelled over densely populated and industrialized regions of mainland China. Group_2 was from air masses with long travel times over the ocean and relatively low total ion concentrations (80–570 µeq.·L⁻¹) and higher pHs (median 4.80). The cleanest samples are among the cleanest reported in the literature of worldwide fog and rain. In both groups, the pH was governed by the balance of sulfate, nitrate, ammonium, and, in some cases, calcium. The variability of these ions was higher than the variability of 10^−pH, which shows that the pH is a rather robust parameter in contrast to its drivers such as non-sea-salt sulfate. Full article

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4596 KiB

Open AccessArticle

Mass Deposition Fluxes of Asian Dust to the Bohai Sea and Yellow Sea from Geostationary Satellite MTSAT: A Case Study

by Qianguang Tu, Zengzhou Hao and Delu Pan

Atmosphere 2015, 6(11), 1771-1784; https://doi.org/10.3390/atmos6111771 - 18 Nov 2015

Cited by 7 | Viewed by 4640

Abstract

Windblown dust aerosol plays an important role in marine ecosystems once they are deposited and dissolved. At present, methods for estimating the deposition flux are mainly limited to direct measurements or model outputs. Additionally, satellite remote sensing was often used to estimate the [...] Read more.

Windblown dust aerosol plays an important role in marine ecosystems once they are deposited and dissolved. At present, methods for estimating the deposition flux are mainly limited to direct measurements or model outputs. Additionally, satellite remote sensing was often used to estimate the integral dust column concentration (DCC). In this paper, an algorithm is developed to estimate the mass deposition fluxes of Asian dust by satellite. The dust aerosol is identified firstly and then the DCC is derived based on the relationships between the pre-calculated lookup table (LUT) and observations from Japanese geostationary Multi-functional Transport Satellites (MTSAT). The LUT is built on the dust cloud and surface parameters by a radiation transfer model Streamer. The average change rate of deposition is derived, which shows an exponential decay dependence on transport time along the pathway. Thus, the deposition flux is acquired via integrating the hourly deposition. This simple algorithm is applied to a dust storm that occurred in the Bohai Sea and Yellow Sea from 1 to 3 March 2008. Results indicate that the properties of the dust cloud over the study area changed rapidly and the mass deposition flux is estimated to be 2.59 Mt. Full article

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6472 KiB

Open AccessArticle

Seasonal Variations of Atmospheric Pollution and Air Quality in Beijing

by Wei Chen, Lei Yan and Haimeng Zhao

Atmosphere 2015, 6(11), 1753-1770; https://doi.org/10.3390/atmos6111753 - 18 Nov 2015

Cited by 49 | Viewed by 7919

Abstract

New ambient air quality standards were released in 2012 and implemented in 2013 with real time monitoring data publication of six atmospheric pollutants: particulate matter (PM)_2.5, PM₁₀, O₃, SO₂, NO₂ and CO. According to [...] Read more.

New ambient air quality standards were released in 2012 and implemented in 2013 with real time monitoring data publication of six atmospheric pollutants: particulate matter (PM)_2.5, PM₁₀, O₃, SO₂, NO₂ and CO. According to the new standards, Beijing began to publicize real-time monitoring data of 35 monitoring stations in 2013. In this study, real time concentrations of all six atmospheric pollutants of all 35 monitoring stations were collected from September 2014 to August 2015 to investigate the spatial and temporal pattern of the air quality and atmospheric pollutants. By comparing the annual and seasonal variations of all six pollutants’ concentrations, it was found that particulate matter, especially PM_2.5, is still the major contributor to the deterioration of air quality in Beijing. Although the NO₂ and O₃ concentrations of some stations were still high under certain circumstances, their contributions to air quality index (AQI) were not comparable to those of PM_2.5 and PM₁₀. SO₂ and CO concentrations have dropped to well below the qualification standards. Winter and autumn were the most polluted seasons for all pollutants except O_3,whose concentrations are higher in summer. South and southeast stations were the most polluted compared with the rest of the stations, especially for particulate matter. Wind profile analysis with heavy pollution situations indicates that low speed southwest or east wind situations have the higher possibility of heavy pollution, suggesting that it is highly possible that long-range transportation of air pollutants from south or east neighboring provinces played an important role in the worsening air conditions in Beijing. Full article

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273 KiB

Open AccessArticle

An Assessment of Air Pollution Exposure Information for Health Studies

by Frederick W. Lipfert

Atmosphere 2015, 6(11), 1736-1752; https://doi.org/10.3390/atmos6111736 - 06 Nov 2015

Cited by 17 | Viewed by 5834

Abstract

Most studies of air pollution health effects are based on outdoor ambient exposures, mainly because of the availability of population-based data and the need to support emission control programs. However, there is also a large body of literature on indoor air quality that [...] Read more.

Most studies of air pollution health effects are based on outdoor ambient exposures, mainly because of the availability of population-based data and the need to support emission control programs. However, there is also a large body of literature on indoor air quality that is more relevant to personal exposures. This assessment attempts to merge these two aspects of pollution-related health effects, emphasizing fine particles. However, the basic concepts are applicable to any pollutant. The objectives are to examine sensitivities of epidemiological studies to the inclusion of personal exposure information and to assess the resulting data requirements. Indoor air pollution results from penetration of polluted outdoor air and from various indoor sources, among which environmental tobacco smoke (ETS) is probably the most toxic and pervasive. Adequate data exist on infiltration of outdoor air but less so for indoor sources and effects, all of which have been based on surveys of small samples of individual buildings. Since epidemiology is based on populations, these data must be aggregated using probabilistic methods. Estimates of spatial variation and precision of ambient air quality are also needed. Hypothetical personal exposures in this paper are based on ranges in outdoor air quality, variable infiltration rates, and ranges of indoor source strength. These uncertainties are examined with respect to two types of mortality studies: time series analysis of daily deaths in a given location, and cross-sectional analysis of annual mortality rates among locations. Regressions of simulated mortality on personal exposures, as affected by all of these uncertainties, are used to examine effects on dose-response functions using quasi-Monte Carlo methods. The working hypothesis is that indoor sources are reasonably steady over time and thus applicable only to long-term cross-sectional studies. Uncertainties in exposure attenuate the simulated mortality regression coefficients; correlations between “true” and hypothesized exposures are used to compare their effects. For a given exposure uncertainty level, attenuation of regression coefficients is similar for both types of simulated mortality studies, but since cross-sectional studies involve indoor sources they are more sensitive, to the point where regression coefficients may be driven to zero. The most pressing need for confirming data is the distribution of indoor sources among cities, especially for ETS. Full article

(This article belongs to the Special Issue Indoor and Outdoor Air Quality)

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3797 KiB

Open AccessArticle

Internal Combustion Engines as the Main Source of Ultrafine Particles in Residential Neighborhoods: Field Measurements in the Czech Republic

by Jitka Stolcpartova, Martin Pechout, Lubos Dittrich, Martin Mazac, Michael Fenkl, Kristyna Vrbova, Jakub Ondracek and Michal Vojtisek-Lom

Atmosphere 2015, 6(11), 1714-1735; https://doi.org/10.3390/atmos6111714 - 05 Nov 2015

Cited by 3 | Viewed by 5744

Abstract

Ultrafine particles (UFP, diameter < 100 nm) exposure has already been associated with adverse effects on human health. Spatial distribution of UFP is non-uniform; they concentrate in the vicinity of the source, e.g. traffic, because of their short lifespan. This work investigates spatial [...] Read more.

Ultrafine particles (UFP, diameter < 100 nm) exposure has already been associated with adverse effects on human health. Spatial distribution of UFP is non-uniform; they concentrate in the vicinity of the source, e.g. traffic, because of their short lifespan. This work investigates spatial distribution of UFP in three areas in the Czech Republic with different traffic load: High traffic (Prague neighborhood—Sporilov), commuter road vicinity (Libeznice), and a small city with only local traffic (Celakovice). Size-resolved measurements of particles in the 5–500 nm range were taken with a particle classifier mounted, along with batteries, GPS and other accessories, on a handcart and pushed around the areas, making one-minute or longer stops at places of interest. Concentrations along main roads were elevated in comparison with places farther from the road; this pattern was observed in all sites, while particle number distributions both close and away from main roads had similar patterns. The absence of larger particles, the relative absence of higher concentrations of particles away from the main roads, and similar number distributions suggest that high particle number concentrations cannot be readily attributed to sources other than internal combustion engines in vehicles and mobile machinery (i.e., mowers and construction machines). Full article

(This article belongs to the Special Issue Indoor and Outdoor Air Quality)

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1298 KiB

Open AccessArticle

A Cluster of CO₂ Change Characteristics with GOSAT Observations for Viewing the Spatial Pattern of CO₂ Emission and Absorption

by Da Liu, Liping Lei, Lijie Guo and Zhao-Cheng Zeng

Atmosphere 2015, 6(11), 1695-1713; https://doi.org/10.3390/atmos6111695 - 05 Nov 2015

Cited by 18 | Viewed by 6010

Abstract

Satellite observations can be used to detect the changes of CO₂ concentration at global and regional scales. With the column-averaged CO₂ dry-air mole fraction (Xco₂) data derived from satellite observations, the issue is how to extract and assess these [...] Read more.

Satellite observations can be used to detect the changes of CO₂ concentration at global and regional scales. With the column-averaged CO₂ dry-air mole fraction (Xco₂) data derived from satellite observations, the issue is how to extract and assess these changes, which are related to anthropogenic emissions and biosphere absorptions. We propose a k-means cluster analysis to extract the temporally changing features of Xco₂ in the Central-Eastern Asia using the data from 2009 to 2013 obtained by Greenhouse Gases Observing Satellite (GOSAT), and assess the effects of anthropogenic emissions and biosphere absorptions on CO₂ changes combining with the data of emission and vegetation net primary production (NPP). As a result, 14 clusters, which are 14 types of Xco₂seasonal changing patterns, are obtained in the study area by using the optimal clustering parameters. These clusters are generally in agreement with the spatial pattern of underlying anthropogenic emissions and vegetation absorptions. According to correlation analysis with emission and NPP, these 14 clusters are divided into three groups: strong emission, strong absorption, and a tendency of balancing between emission and absorption. The proposed clustering approach in this study provides us with a potential way to better understand how the seasonal changes of CO₂ concentration depend on underlying anthropogenic emissions and vegetation absorptions. Full article

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547 KiB

Open AccessArticle

Exposure Assessment of Allergens and Metals in Settled Dust in French Nursery and Elementary Schools

by Nuno Canha, Corinne Mandin, Olivier Ramalho, Guillaume Wyart, Jacques Ribéron, Claire Dassonville and Mickael Derbez

Atmosphere 2015, 6(11), 1676-1694; https://doi.org/10.3390/atmos6111676 - 05 Nov 2015

Cited by 12 | Viewed by 5595

Abstract

The aim of this study was to characterise the contamination in settled dust in French classrooms and to provide an overview of the influencing factors of dust contamination. Cat, dog and dust mite allergens and metals were measured in 51 classrooms at 17 [...] Read more.

The aim of this study was to characterise the contamination in settled dust in French classrooms and to provide an overview of the influencing factors of dust contamination. Cat, dog and dust mite allergens and metals were measured in 51 classrooms at 17 schools. The concentrations of pet allergens in settled dust were generally low (mean value of 0.1 µg·g⁻¹), with carpeted and rug-covered floors presenting higher dust and cat allergen concentrations. The highest metal loadings in dust were observed for manganese (Mn) and copper (Cu), while the lead (Pb) loadings were lower (16 ± 19 µg·m⁻²) and fell below the French guideline. Higher metal leachability was found for cadmium (Cd), Cu, Pb and strontium (Sr) at values of approximately 80%, which suggest that, in cases of dust ingestion by children, a large proportion should be assimilated through the gastro-intestinal tract. The intra-classroom and intra-school variabilities of the metal concentrations in settled dust were lower than the variability between schools. Classrooms with tiled floors had higher Pb loadings than classrooms with wood or vinyl floors. In addition, wet cleaning less than once a week resulted in greater loadings of Cu and Pb in the settled dust. Lastly, enrichment factors showed that metals in settled dust of classrooms were not only from the contribution of the natural background concentrations in soils. Full article

(This article belongs to the Special Issue Indoor and Outdoor Air Quality)

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652 KiB

Open AccessArticle

Indoor Air Quality in Naturally Ventilated Italian Classrooms

by Fernanda Carmen Fuoco, Luca Stabile, Giorgio Buonanno, Concepcion Vargas Trassiera, Angelamaria Massimo, Aldo Russi, Mandana Mazaheri, Lidia Morawska and Alexandro Andrade

Atmosphere 2015, 6(11), 1652-1675; https://doi.org/10.3390/atmos6111652 - 02 Nov 2015

Cited by 47 | Viewed by 8980

Abstract

Characterization of indoor air quality in school classrooms is crucial to children’s health and performance. The present study was undertaken to characterize the indoor air quality in six naturally ventilated classrooms of three schools in Cassino (Italy). Indoor particle number, mass, black carbon, [...] Read more.

Characterization of indoor air quality in school classrooms is crucial to children’s health and performance. The present study was undertaken to characterize the indoor air quality in six naturally ventilated classrooms of three schools in Cassino (Italy). Indoor particle number, mass, black carbon, CO₂ and radon concentrations, as well as outdoor particle number were measured within school hours during the winter and spring season. The study found the concentrations of indoor particle number were influenced by the concentrations in the outdoors; highest BC values were detected in classrooms during peak traffic time. The effect of different seasons’ airing mode on the indoor air quality was also detected. The ratio between indoor and outdoor particles was of 0.85 ± 0.10 in winter, under airing conditions of short opening window periods, and 1.00 ± 0.15 in spring when the windows were opened for longer periods. This was associated to a higher degree of penetration of outdoor particles due to longer period of window opening. Lower CO₂ levels were found in classrooms in spring (908 ppm) than in winter (2206 ppm). Additionally, a greater reduction in radon concentrations was found in spring. In addition, high PM₁₀ levels were found in classrooms during break time due to re-suspension of coarse particles. Full article

(This article belongs to the Special Issue Indoor and Outdoor Air Quality)

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6536 KiB

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The Influence of Sandstorms and Long-Range Transport on Polycyclic Aromatic Hydrocarbons (PAHs) in PM_2.5 in the High-Altitude Atmosphere of Southern China

by Minmin Yang, Yan Wang, Qiang Liu, Aijun Ding and Yuhua Li

Atmosphere 2015, 6(11), 1633-1651; https://doi.org/10.3390/atmos6111633 - 30 Oct 2015

Cited by 16 | Viewed by 6370

Abstract

PM_2.5 (Particulate Matter 2.5) samples were collected at Mount Heng and analyzed for polycyclic aromatic hydrocarbons (PAHs). During sampling, a sandstorm from northern China struck Mount Heng and resulted in a mean PM_2.5 concentration of 150.61 μg/m³, which greatly [...] Read more.

PM_2.5 (Particulate Matter 2.5) samples were collected at Mount Heng and analyzed for polycyclic aromatic hydrocarbons (PAHs). During sampling, a sandstorm from northern China struck Mount Heng and resulted in a mean PM_2.5 concentration of 150.61 μg/m³, which greatly exceeded the concentration measured under normal conditions (no sandstorm: 58.50 μg/m³). The average mass of PAHs in PM_2.5 was 30.70 μg/g, which was much lower than in the non-sandstorm samples (80.80 μg/g). Therefore, the sandstorm increased particle levels but decreased PAH concentrations due to dilution and turbulence. During the sandstorm, the concentrations of 4- and 5-ring PAHs were below their detection limits, and 6-ring PAHs were the most abundant. Under normal conditions, the concentrations of 2-, 3- and 6-ring PAHs were higher, and 4- and 5-ring PAHs were lower relative to the other sampling sites. In general, the PAH contamination was low to medium at Mount Heng. Higher LMW (low molecular weight) concentrations were primarily linked to meteorological conditions, and higher HMW (high molecular weight) concentrations primarily resulted from long-range transport. Analysis of diagnostic ratios indicated that PM_2.5 PAHs had been emitted during the combustion of coal, wood or petroleum. The transport characteristics and origins of the PAHs were investigated using backwards Lagrangian particle dispersion modeling. Under normal conditions, the “footprint” retroplumes and potential source contributions of PAHs for the highest and lowest concentrations indicated that local sources had little effect. In contrast, long-range transport played a vital role in the levels of PM_2.5 and PAHs in the high-altitude atmosphere. Full article

(This article belongs to the Special Issue Atmospheric Composition Observations)

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1085 KiB

Open AccessArticle

On the Importance of Aerosol Composition for Estimating Incoming Solar Radiation: Focus on the Western African Stations of Dakar and Niamey during the Dry Season

by Mamadou Simina Drame, Xavier Ceamanos, Jean Louis Roujean, Aaron Boone, Jean Philippe Lafore, Dominique Carrer and Olivier Geoffroy

Atmosphere 2015, 6(11), 1608-1632; https://doi.org/10.3390/atmos6111608 - 29 Oct 2015

Cited by 14 | Viewed by 6340

Abstract

The article investigates the impact of aerosol composition on the estimation of the downwelling surface shortwave flux (DSSF). This initiative forms part of the efforts to improve the DSSF distributed by the Land Surface Analysis Satellite Application Facility (LSA-SAF). This operational product assumes [...] Read more.

The article investigates the impact of aerosol composition on the estimation of the downwelling surface shortwave flux (DSSF). This initiative forms part of the efforts to improve the DSSF distributed by the Land Surface Analysis Satellite Application Facility (LSA-SAF). This operational product assumes invariant aerosol properties under clear sky conditions, which can be inaccurate for some regions of the world. This is the case of West Africa, where aerosol activity is not only highly variable due to frequent dust storms but also rich because of the coexistence of different aerosol species. This study was carried out over the West African stations of Dakar and Niamey, which represent different aerosol scenarios. Several dates during the dry season of 2006 were selected and classified into four different day types according to aerosol activity: standard, clean, mixture and dusty days. The diurnal evolution of DSSF and its direct and diffuse components were estimated for the selected dates by the current LSA-SAF algorithm and two other approaches using aerosol measurements from the Aerosol Robotic Network (AERONET) as input. The first alternative approach took the diurnal evolution of the total aerosol optical depth (AOD) into account, assuming a default desert aerosol type. Experiments with this method showed a significant improvement in the estimated DSSF compared to the current LSA-SAF algorithm. For example, root mean square error (RMSE) improved from 170 W/m² to 50 W/m² for dusty days in Dakar and from 73 W/m² to 21 W/m² for mixture days in Niamey. This improvement resulted from the consideration of a time-varying AOD, which accounted for the rapidly changing aerosol load for these two day types. The second alternative approach tested included consideration of the diurnal variation of the aerosol load and composition. Again, this was done using AERONET data on the fine and coarse aerosol modes, which may be associated with different sized dust particles, sea salt, or soot from biomass burning (depending on the date). This enhanced consideration of the aerosol composition greatly improved the estimation of the diffuse component of the DSSF, further reducing the RMSE during mixture days from 50 W/m² to less than 10 W/m². This improvement mainly came from consideration of the right scattering properties of the aerosol particles, which may be significantly different for each aerosol type. Full article

(This article belongs to the Special Issue Atmospheric Aerosols and Their Radiative Effects)

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1028 KiB

Open AccessArticle

CCN Properties of Organic Aerosol Collected Below and within Marine Stratocumulus Clouds near Monterey, California

by Akua Asa-Awuku, Armin Sorooshian, Richard C. Flagan, John H. Seinfeld and Athanasios Nenes

Atmosphere 2015, 6(11), 1590-1607; https://doi.org/10.3390/atmos6111590 - 28 Oct 2015

Cited by 8 | Viewed by 5555

Abstract

The composition of aerosol from cloud droplets differs from that below cloud. Its implications for the Cloud Condensation Nuclei (CCN) activity are the focus of this study. Water-soluble organic matter from below cloud, and cloud droplet residuals off the coast of Monterey, California [...] Read more.

The composition of aerosol from cloud droplets differs from that below cloud. Its implications for the Cloud Condensation Nuclei (CCN) activity are the focus of this study. Water-soluble organic matter from below cloud, and cloud droplet residuals off the coast of Monterey, California were collected; offline chemical composition, CCN activity and surface tension measurements coupled with Köhler Theory Analysis are used to infer the molar volume and surfactant characteristics of organics in both samples. Based on the surface tension depression of the samples, it is unlikely that the aerosol contains strong surfactants. The activation kinetics for all samples examined are consistent with rapid (NH₄)₂SO₄ calibration aerosol. This is consistent with our current understanding of droplet kinetics for ambient CCN. However, the carbonaceous material in cloud drop residuals is far more hygroscopic than in sub-cloud aerosol, suggestive of the impact of cloud chemistry on the hygroscopic properties of organic matter. Full article

(This article belongs to the Special Issue Atmospheric Composition Observations)

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Atmosphere, Volume 6, Issue 11 (November 2015) – 14 articles , Pages 1590-1857

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