scholarly journals Chemical composition and aerosol size distribution of the middle mountain range in the Nepal Himalayas during the 2009 pre-monsoon season

2010 ◽  
Vol 10 (23) ◽  
pp. 11605-11621 ◽  
Author(s):  
P. Shrestha ◽  
A. P. Barros ◽  
A. Khlystov
Keyword(s):  
Boundary Layer ◽  
Chemical Composition ◽  
Organic Carbon ◽  
Size Distribution ◽  
Elemental Carbon ◽  
Monsoon Season ◽  
Number Concentration ◽  
Water Soluble ◽  
Aerosol Size Distribution ◽  
Aerosol Number Concentration

Abstract. Aerosol particle number size distribution and chemical composition were measured at two low altitude sites, one urban and one relatively pristine valley, in Central Nepal during the 2009 pre-monsoon season (May–June). This is the first time that aerosol size distribution and chemical composition were measured simultaneously at lower elevations in the middle Himalayan region in Nepal. The aerosol size distribution was measured using a Scanning Mobility Particle Sizer (SMPS, 14–340 nm), and the chemical composition of the filter samples collected during the field campaign was analyzed in the laboratory. Teflon membrane filters were used for ion chromatography (IC) and water-soluble organic carbon and nitrogen analysis. Quartz fiber filters were used for organic carbon and elemental carbon analysis. Multi-lognormal fits to the measured aerosol size distribution indicated a consistent larger mode around 100 nm which is usually the oldest, most processed background aerosol. The smaller mode was located around 20 nm, which is indicative of fresh but not necessarily local aerosol. The diurnal cycle of the aerosol number concentration showed the presence of two peaks (early morning and evening), during the transitional periods of boundary layer growth and collapse. The increase in number concentration during the peak periods was observed for the entire size distribution. Although the possible contribution of local emissions in size ranges similar to the larger mode cannot be completely ruled out, another plausible explanation is the mixing of aged elevated aerosol in the residual layer during the morning period as suggested by previous studies. Similarly, the evening time concentration peaks when the boundary layer becomes shallow concurrent with increase in local activity. A decrease in aerosol number concentration was observed during the nighttime with the development of cold (downslope) mountain winds that force the low level warmer air in the valley to rise. The mountain valley wind mechanisms induced by the topography along with the valley geometry appear to have a strong control in the diurnal cycle of the aerosol size distribution. During the sampling period, the chemical composition of PM2.5 was dominated by organic matter at both sites. Organic carbon (OC) comprised the major fraction (64–68%) of the aerosol concentration followed by ionic species (24–26%, mainly SO42− and NH4+). Elemental Carbon (EC) compromised 7–10% of the total composition and 27% of OC was found to be water soluble at both sites. The day-to-day variability observed in the time series of aerosol composition could be explained by the synoptic scale haze that extended to the sampling region from the Indian Gangetic Plain (IGP), and rainfall occurrence. In the presence of regional scale haze during dry periods, the mean volume aerosol concentration was found to increase and so did the aerosol mass concentrations.

scholarly journals Chemical composition and aerosol size distribution of the middle mountain range in the Nepal Himalayas during the 2009 pre-monsoon season

2010 ◽  
Vol 10 (6) ◽  
pp. 15629-15670
Author(s):  
P. Shrestha ◽  
A. P. Barros ◽  
A. Khlystov
Keyword(s):  
Boundary Layer ◽  
Chemical Composition ◽  
Organic Carbon ◽  
Size Distribution ◽  
Elemental Carbon ◽  
Monsoon Season ◽  
Number Concentration ◽  
Water Soluble ◽  
Aerosol Size Distribution ◽  
Aerosol Number Concentration

Abstract. Aerosol particle number size distribution and chemical composition were measured at two low altitude sites, one urban and one relatively pristine valley, in Central Nepal during the 2009 pre-monsoon season (May–June). This is the first time that aerosol size distribution and chemical composition were measured simultaneously at lower elevation in the Middle Himalayan region in Nepal. The aerosol size distribution was measured using a Scanning Mobility Particle Sizer (SMPS, 14~340 nm), and the chemical composition of the filter samples collected during the field campaign was analyzed in the laboratory. Teflon membrane filters were used for ion chromatography (IC) and water-soluble organic carbon and nitrogen analysis. Quartz fiber filters were used for organic carbon and elemental carbon analysis. Multi-lognormal fits to the measured aerosol size distribution indicated a consistent larger mode around 100 nm which is usually the oldest, most processed background aerosol. The smaller mode was located around 20 nm, which is indicative of fresh but not necessarily local aerosol. The diurnal cycle of the aerosol number concentration showed the presence of two peaks (early morning and evening), during the transitional period of boundary layer growth and collapse. The increase in number concentration during the peak period was observed for the entire size distribution. Although the possible contribution of local emissions in size ranges similar to the larger mode cannot be completely ruled out, another plausible explanation is the mixing of aged elevated aerosol in the residual layer during the morning period as suggested by previous studies. Similarly, the evening time concentration peaks when the boundary layer becomes shallow concurrent with increase in local activity. A decrease in aerosol number concentration was observed during the nighttime with the development of cold (downslope) mountain winds that force the low level warmer air in the valley to rise. The mountain valley wind mechanisms induced by the topography along with the valley geometry appear to have a strong control in the diurnal cycle of the aerosol size distribution. During the sampling period, the chemical composition of PM2.5 was dominated by organic matter at both sites. Organic carbon (OC) comprised the major fraction (64~68%) of the aerosol concentration followed by ionic species (24~26% mainly SO42- and NH4+). Elemental Carbon (EC) compromised 7~10% of the total composition. A large fraction of OC was found to be water soluble (nearly 27% at both sites).

Estimating the Sensitivity of Radiative Impacts of Shallow, Broken Marine Clouds to Boundary Layer Aerosol Size Distribution Parameter Uncertainties for Evaluation of Satellite Retrieval Requirements

2011 ◽  
Vol 28 (4) ◽  
pp. 530-538 ◽  
Author(s):  
Ann M. Fridlind ◽  
Andrew S. Ackerman
Keyword(s):  
Boundary Layer ◽  
Size Distribution ◽  
Case Studies ◽  
Number Concentration ◽  
Effective Radius ◽  
Aerosol Size Distribution ◽  
Parameter Uncertainties ◽  
Analytic Estimate ◽  
Aerosol Number Concentration ◽  
Aerosol Properties

Abstract A proposed objective of the planned Aerosol–Cloud–Ecosystem (ACE) satellite mission is to provide constraints on climate model representation of aerosol effects on clouds by retrieving profiles of aerosol number concentration, effective variance, and effective radius over the 0.1–1-μm radius range under humidified ambient conditions with 500-m vertical resolution and uncertainties of 100%, 50%, and 10%, respectively. Shallow, broken marine clouds provide an example of conditions where boundary layer aerosol properties would be retrieved in clear-sky gaps. To quantify the degree of constraint that proposed retrievals might provide on cloud radiative forcing (CRF) simulated by climate models under such conditions, dry aerosol size distribution parameters are independently varied here in large-eddy simulations of three well-established modeling case studies. Using the rudimentary available aerosol specifications, it is found that relative changes of total dry aerosol properties in simulations can be used as a proxy for relative changes of ambient aerosol properties targeted by ACE retrievals. The sensitivity of simulated daytime shortwave CRF to the proposed uncertainty in retrieved aerosol number concentration is −15 W m−2 in the overcast limit, roughly a factor of 2 smaller than a simple analytic estimate owing primarily to aerosol-induced reductions in simulated liquid water path across this particular set of case studies. The CRF sensitivity to proposed uncertainties in retrieved aerosol effective variance and effective radius is typically far smaller, with no corresponding analytic estimate. Generalization of the results obtained here using only three case studies would require statistical analysis of relevant meteorological and aerosol observations and quantification of observational and model uncertainties and biases.

scholarly journals On the competition among aerosol number, size and composition in predicting CCN variability: a multi-annual field study in an urbanized desert

2015 ◽  
Vol 15 (12) ◽  
pp. 6943-6958 ◽  
Author(s):  
E. Crosbie ◽  
J.-S. Youn ◽  
B. Balch ◽  
A. Wonaschütz ◽  
T. Shingler ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Size Distribution ◽  
North American ◽  
Monsoon Season ◽  
Aerosol Size Distribution ◽  
North American Monsoon ◽  
Aerosol Composition ◽  
Data Set ◽  
The North ◽  
Concentration Changes

Abstract. A 2-year data set of measured CCN (cloud condensation nuclei) concentrations at 0.2 % supersaturation is combined with aerosol size distribution and aerosol composition data to probe the effects of aerosol number concentrations, size distribution and composition on CCN patterns. Data were collected over a period of 2 years (2012–2014) in central Tucson, Arizona: a significant urban area surrounded by a sparsely populated desert. Average CCN concentrations are typically lowest in spring (233 cm−3), highest in winter (430 cm−3) and have a secondary peak during the North American monsoon season (July to September; 372 cm−3). There is significant variability outside of seasonal patterns, with extreme concentrations (1 and 99 % levels) ranging from 56 to 1945 cm−3 as measured during the winter, the season with highest variability. Modeled CCN concentrations based on fixed chemical composition achieve better closure in winter, with size and number alone able to predict 82 % of the variance in CCN concentration. Changes in aerosol chemical composition are typically aligned with changes in size and aerosol number, such that hygroscopicity can be parameterized even though it is still variable. In summer, models based on fixed chemical composition explain at best only 41 % (pre-monsoon) and 36 % (monsoon) of the variance. This is attributed to the effects of secondary organic aerosol (SOA) production, the competition between new particle formation and condensational growth, the complex interaction of meteorology, regional and local emissions and multi-phase chemistry during the North American monsoon. Chemical composition is found to be an important factor for improving predictability in spring and on longer timescales in winter. Parameterized models typically exhibit improved predictive skill when there are strong relationships between CCN concentrations and the prevailing meteorology and dominant aerosol physicochemical processes, suggesting that similar findings could be possible in other locations with comparable climates and geography.

scholarly journals Size-Segregated Characteristics of Carbonaceous Aerosols during the Monsoon and Non-Monsoon Seasons in Lhasa in the Tibetan Plateau

Atmosphere ◽  
2019 ◽  
Vol 10 (3) ◽  
pp. 157 ◽  
Author(s):  
Nannan Wei ◽  
Chulei Ma ◽  
Junwen Liu ◽  
Guanghua Wang ◽  
Wei Liu ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Organic Carbon ◽  
Size Distribution ◽  
Fossil Fuels ◽  
Monsoon Season ◽  
Water Soluble ◽  
Atmospheric Particulate Matter ◽  
The Tibetan Plateau ◽  
Carbonaceous Aerosols ◽  
Different Diameters

In this paper, we intensively collected atmospheric particulate matter (PM) with different diameters (size ranges: <0.49, 0.49–0.95, 0.95–1.5, 1.5–3.0, 3.0–7.2, and >7.2 μm) in Lhasa during the monsoon and non-monsoon seasons. The results clearly showed that the concentrations of PM, organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon (WSOC) during the non-monsoon season were much higher than the concentrations during the monsoon season. During the monsoon season, a bimodal size distribution of the OC and WSOC, which were at <0.49 μm and >7.2 μm, respectively, and a unimodal size distribution at <0.49 μm for the EC were observed. However, during the non-monsoon season, there was a trimodal size distribution of the OC and WSOC (<0.49 μm, 1.5–3.0 μm, and >7.2 μm), and a unimodal size distribution of the EC (<0.49 μm). Possible sources of the carbonaceous components were revealed by combining the particle size distribution and the correlation analysis. OC, EC, and WSOC were likely from the photochemical transformation of biogenic and anthropogenic VOC, and the incomplete combustion of biomass burning and fossil fuels at <0.49 μm, whilst they were also likely to be from various types of dust and biogenic aerosols at >7.2 μm. OC and WSOC at 1.5–3.0 μm were likely to have been from the burning of yak dung and photochemical formation. The above results may draw attention in the public and scientific communities to the issues of air quality in the Tibetan Plateau.

scholarly journals Earth System Model Aerosol-Cloud Diagnostics Package (ESMAC Diags) Version 1: Assessing E3SM Aerosol Predictions Using Aircraft, Ship, and Surface Measurements

2021 ◽  
Author(s):  
Shuaiqi Tang ◽  
Jerome D. Fast ◽  
Kai Zhang ◽  
Joseph C. Hardin ◽  
Adam C. Varble ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Size Distribution ◽  
Number Concentration ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Aerosol Cloud ◽  
Surface Measurements ◽  
Aerosol Number Concentration ◽  
Aerosol Properties

Abstract. An Earth System Model (ESM) aerosol-cloud diagnostics package is developed to facilitate the routine evaluation of aerosols, clouds and aerosol-cloud interactions simulated by the Department of Energy’s (DOE) Energy Exascale Earth System Model (E3SM). The first version focuses on comparing simulated aerosol properties with aircraft, ship, and surface measurements, most of them are measured in-situ. The diagnostics currently covers six field campaigns in four geographical regions: Eastern North Atlantic (ENA), Central U.S. (CUS), Northeastern Pacific (NEP) and Southern Ocean (SO). These regions produce frequent liquid or mixed-phase clouds with extensive measurements available from the Atmospheric Radiation Measurement (ARM) program and other agencies. Various types of diagnostics and metrics are performed for aerosol number, size distribution, chemical composition, CCN concentration and various meteorological quantities to assess how well E3SM represents observed aerosol properties across spatial scales. Overall, E3SM qualitatively reproduces the observed aerosol number concentration, size distribution and chemical composition reasonably well, but underestimates Aitken mode and overestimates accumulation mode aerosols over the CUS region, and underestimates aerosol number concentration over the SO region. The current version of E3SM struggles to reproduce new particle formation events frequently observed over both the CUS and ENA regions, indicating missing processes in current parameterizations. The diagnostics package is coded and organized in a way that can be easily extended to other field campaign datasets and adapted to higher-resolution model simulations. Future releases will include comprehensive cloud and aerosol-cloud interaction diagnostics.

scholarly journals On the competition among aerosol number, size and composition in predicting CCN variability: a multi-annual field study in an urbanized desert

2015 ◽  
Vol 15 (3) ◽  
pp. 3863-3906
Author(s):  
E. Crosbie ◽  
J.-S. Youn ◽  
B. Balch ◽  
A. Wonaschütz ◽  
T. Shingler ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Size Distribution ◽  
North American ◽  
Monsoon Season ◽  
Aerosol Size Distribution ◽  
North American Monsoon ◽  
Aerosol Chemistry ◽  
The North ◽  
Predictive Skill ◽  
Concentration Changes

Abstract. A two-year dataset of measured CCN concentrations at 0.2% supersaturation is combined with aerosol size distribution and aerosol chemistry data to probe the effects of aerosol number concentrations, size distribution and composition on CCN patterns. Data have been collected over a period of two years (2012–2014) in central Tucson, Arizona: a significant urban area surrounded by a sparsely populated desert. Average CCN concentrations are typically lowest in spring (233 cm−3), highest in winter (430 cm−3) and have a secondary peak during the North American Monsoon season (July to September; 372 cm−3). There is significant variability outside of seasonal patterns with extreme concentrations (1 and 99% levels) ranging from 56 to 1945 cm−3 as measured during the winter, the season with highest variability. Modeled CCN concentrations based on fixed chemical composition achieve better closure in winter, with size and number alone able to predict 82% of the variance in CCN concentration. Changes in aerosol chemistry are typically aligned with changes in size and aerosol number, such that composition can be parameterized even though it is still variable. In summer, models based on fixed chemical composition explain at best only 41% (pre-monsoon) and 36% (monsoon) of the variance. This is attributed to the effects of secondary organic aerosol (SOA) production, the competition between new particle formation and condensational growth, and the complex interaction of meteorology, regional and local emissions, and multi-phase chemistry during the North American Monsoon. Chemical composition is found to be an important factor for improving predictability in spring and on longer timescales in winter. Regimes where parameterized models exhibit improved predictive skill are typically explained by strong relationships between CCN concentrations and the prevailing meteorology and dominant aerosol chemistry mechanisms suggesting that similar findings could be possible in other locations with comparable climates and geography.

scholarly journals Seasonal variation of aerosol size distribution at Puy de Dôme (1465 m a.s.l., central France)

2008 ◽  
Vol 8 (4) ◽  
pp. 15791-15824 ◽  
Author(s):  
H. Venzac ◽  
K. Sellegri ◽  
P. Villani ◽  
D. Picard ◽  
P. Laj
Keyword(s):  
Boundary Layer ◽  
Size Distribution ◽  
Total Concentration ◽  
Winter Season ◽  
Number Concentration ◽  
Aerosol Size Distribution ◽  
Research Station ◽  
Size Distributions ◽  
Free Troposphere ◽  
Air Mass

Abstract. Particle number concentration and size distribution are amongst the most important variables needed to constrain the role of the atmospheric particles in the Earth radiative budget. They are also linked to regulated variables such as particle mass (PM) and therefore of interest to air quality studies. However, data on their long-term variability are scarce, in particular at high altitudes where the occurrence of aerosol in elevated layers cannot be resolved from most instruments in space. Therefore it is crucial to provide ground based measurements of suited aerosol variables to obtain closure between all independent information sources. In this paper, we investigate diurnal and seasonal variability of aerosol number concentration and size distribution at the Puy de Dôme research station (France, 1465 m a.s.l.). We report variability of aerosol particle total number concentration measured over a five years (2003–2007) period and aerosol size distributions over a one year period (January to December 2006). Concentrations show a strong seasonality with maxima during summer and minima during winter. A diurnal variation is also observed with maxima between 12:00 and 18:00 UTC. At night (00:00–06:00 UTC), the median hourly total concentration varies from 600 to 800 cm−3 during winter and from 1700 to 2200 cm−3 during summer. During the day (08:00–18:00 UTC), the concentration is in the range of 700 to 1400 cm−3 during winter and from 2500 to 3500 cm−3 during summer. An averaged size distribution of particles (10–500 nm) was calculated for each season. A variability in the size of aerosols sampled at the Puy de Dôme is also observed on the seasonal and diurnal basis. Because the site lies in the free troposphere only a fraction of the time, in particular at night and during the winter season, we have subsequently analyzed the variability for free tropospheric conditions only. We show that the variability is due to both seasonal changes in air mass origin from winter to summer and enhanced concentration of the free troposphere in summer. The later observation can be explained by higher emission intensity in the boundary layer, stronger exchange between the boundary layer and the free troposphere as well as enhanced photochemical processes. Finally, aerosol mean size distributions are calculated for a given air mass type (marine/continental/regional) according to the season, for the specific conditions of the free troposphere. These results are of regional relevance and can be used to constrain chemical-transport models over Western Europe.

scholarly journals Aerosol characteristics in the entrainment interface layer in relation to the marine boundary layer and free troposphere

2018 ◽  
Vol 18 (3) ◽  
pp. 1495-1506 ◽  
Author(s):  
Hossein Dadashazar ◽  
Rachel A. Braun ◽  
Ewan Crosbie ◽  
Patrick Y. Chuang ◽  
Roy K. Woods ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Size Distribution ◽  
Surface Area ◽  
Particle Number ◽  
Interface Layer ◽  
Number Concentration ◽  
Aerosol Size Distribution ◽  
Free Troposphere ◽  
Turbulent Layer ◽  
Concentration Difference

Abstract. This study uses airborne data from two field campaigns off the California coast to characterize aerosol size distribution characteristics in the entrainment interface layer (EIL), a thin and turbulent layer above marine stratocumulus cloud tops, which separates the stratocumulus-topped boundary layer (STBL) from the free troposphere (FT). The vertical bounds of the EIL are defined in this work based on considerations of buoyancy and turbulence using thermodynamic and dynamic data. Aerosol number concentrations are examined from three different probes with varying particle diameter (Dp) ranges: > 3 nm, > 10 nm, and 0.11–3.4 µm. Relative to the EIL and FT layers, the sub-cloud (SUB) layer exhibited lower aerosol number concentrations and higher surface area concentrations. High particle number concentrations between 3 and 10 nm in the EIL are indicative of enhanced nucleation, assisted by high actinic fluxes, cool and moist air, and much lower surface area concentrations than the STBL. Slopes of number concentration versus altitude in the EIL were correlated with the particle number concentration difference between the SUB and lower FT layers. The EIL aerosol size distribution was influenced by varying degrees from STBL aerosol versus subsiding FT aerosol depending on the case examined. These results emphasize the important role of the EIL in influencing nucleation and aerosol–cloud–climate interactions.

scholarly journals Aerosol Characteristics in the Entrainment Interface Layer In Relation to the Marine Boundary Layer and Free Troposphere

2017 ◽  
Author(s):  
Hossein Dadashazar ◽  
Rachel A. Braun ◽  
Ewan Crosbie ◽  
Patrick Y. Chuang ◽  
Roy K. Woods ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Size Distribution ◽  
Surface Area ◽  
Particle Number ◽  
Interface Layer ◽  
Number Concentration ◽  
Aerosol Size Distribution ◽  
Free Troposphere ◽  
Turbulent Layer ◽  
Concentration Difference

Abstract. This study uses airborne data from two field campaigns off the California coast to characterize aerosol size distribution characteristics in the entrainment interface layer (EIL), a thin and turbulent layer above marine stratocumulus cloud tops, that separates the stratocumulus-topped boundary layer (STBL) from the free troposphere (FT). The vertical bounds of the EIL are defined in this work based on considerations of buoyancy and turbulence using thermodynamic and dynamic data. Aerosol number concentrations are examined from three different probes with varying particle diameter (Dp) ranges: > 3 nm, > 10 nm, 0.11–3.4 µm. Relative to the EIL and FT layers, the sub-cloud (SUB) layer exhibited lower aerosol number concentrations and higher surface area concentrations. High particle number concentrations between 3 and 10 nm in the EIL is indicative of enhanced nucleation, assisted by high actinic fluxes, cool and moist air, and much lower surface area concentrations than the STBL. Slopes of number concentration versus altitude in the EIL were correlated with the particle number concentration difference between the SUB and lower FT layers. The EIL aerosol size distribution was influenced by varying degrees from STBL aerosol versus subsiding FT aerosol depending on the case examined. These results emphasize the important role of the EIL in influencing nucleation and aerosol-cloud-climate interactions.  

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