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The effect of meteorological and chemical factors on the agreement between observations and predictions of fine aerosol composition in southwestern Ontario during BAQS-Met
Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 7. Markovic M.Z.; Hayden K.L.; Murphy J.G.; et al. - Copernicus GmbH, 2011The Border Air Quality and Meteorology Study (BAQS-Met) was an intensive, collaborative field campaign during the summer of 2007 that investigated the effects of transboundary pollution, local pollution, and local meteorology on air quality in southwestern Ontario. This analysis focuses on the measurements of the inorganic constituents of particulate matter with diameter of less than 1 μm (PM1), with a specific emphasis on nitrate. We evaluate the ability of AURAMS, Environment Canada's chemical transport model, to represent regional air pollution in SW Ontario by comparing modelled aerosol in ...
[article]The effect of meteorological and chemical factors on the agreement between observations and predictions of fine aerosol composition in southwestern Ontario during BAQS-Met
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Available online: http://dx.doi.org/10.5194/acp-11-3195-2011
M.Z. Markovic ; K.L. Hayden ; J.G. Murphy ; P.A. Makar ; R.A. Ellis ; R.Y.-W. Chang ; J.G. Slowik ; C. Mihele ; J. Brook
in Atmospheric Chemistry and Physics (ACP) > Vol. 11. N° 7 [04/01/2011] . - p.3195-3210The Border Air Quality and Meteorology Study (BAQS-Met) was an intensive, collaborative field campaign during the summer of 2007 that investigated the effects of transboundary pollution, local pollution, and local meteorology on air quality in southwestern Ontario. This analysis focuses on the measurements of the inorganic constituents of particulate matter with diameter of less than 1 μm (PM1), with a specific emphasis on nitrate. We evaluate the ability of AURAMS, Environment Canada's chemical transport model, to represent regional air pollution in SW Ontario by comparing modelled aerosol inorganic chemical composition with measurements from Aerosol Mass Spectrometers (AMS) onboard the National Research Council (NRC) of Canada Twin Otter aircraft and at a ground site in Harrow, ON. The agreement between modelled and measured pNO3− at the ground site (observed mean (Mobs) = 0.50 μg m−3; modelled mean (Mmod) = 0.58 μg m−3; root mean square error (RSME) = 1.27 μg m−3) was better than aloft (Mobs = 0.32 μg m−3; Mmod = 0.09 μg m−3; RSME = 0.48 μg m−3). Possible reasons for discrepancies include errors in (i) emission inventories, (ii) atmospheric chemistry, (iii) predicted meteorological parameters, or (iv) gas/particle thermodynamics in the model framework. Using the inorganic thermodynamics model, ISORROPIA, in an offline mode, we find that the assumption of thermodynamic equilibrium is consistent with observations of gas and particle composition at Harrow. We develop a framework to assess the sensitivity of PM1 nitrate to meteorological and chemical parameters and find that errors in both the predictions of relative humidity and free ammonia (FA ≡ NH3(g) + pNH4+ − 2 · pSO42-) are responsible for the poor agreement between modelled and measured values.
Language(s): English
Format: Digital (Free)Tags: Aerosols ; Atmosphere ; Meteorology ; Observations ; Weather forecasting ; Research ; Canada
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The Smithsonian solar constant data revisited: no evidence for a strong effect of solar activity in ground-based insolation data
Apparent evidence for a strong signature of solar activity in ground-based insolation data was recently reported. In particular, a strong increase of the irradiance of the direct solar beam with sunspot number as well as a decline of the brightness of the solar aureole and the measured precipitable water content of the atmosphere with solar activity were presented. The latter effect was interpreted as evidence for cosmic-ray-induced aerosol formation. Here I show that these spurious results are due to a failure to correct for seasonal variations and the effects of volcanic eruptions and local ...
[article]The Smithsonian solar constant data revisited: no evidence for a strong effect of solar activity in ground-based insolation data
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Available online: http://dx.doi.org/10.5194/acp-11-3291-2011
in Atmospheric Chemistry and Physics (ACP) > Vol. 11. N° 7 [04/01/2011] . - p.3291-3301Apparent evidence for a strong signature of solar activity in ground-based insolation data was recently reported. In particular, a strong increase of the irradiance of the direct solar beam with sunspot number as well as a decline of the brightness of the solar aureole and the measured precipitable water content of the atmosphere with solar activity were presented. The latter effect was interpreted as evidence for cosmic-ray-induced aerosol formation. Here I show that these spurious results are due to a failure to correct for seasonal variations and the effects of volcanic eruptions and local pollution in the data. After correcting for these biases, neither the atmospheric water content nor the brightness of the solar aureole show any significant change with solar activity, and the variations of the solar-beam irradiance with sunspot number are in agreement with previous estimates. Hence there is no evidence for the influence of solar activity on the climate being stronger than currently thought.
Language(s): English
Format: Digital (Free)Tags: Sunniness ; Meteorological instrument ; Solar radiation ; Research
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Atmospheric degradation of 3-methylfuran: kinetic and products study
Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 7. Tapia A.; Villanueva F.; Salgado M.S.; et al. - Copernicus GmbH, 2011A study of the kinetics and products obtained from the reactions of 3-methylfuran with the main atmospheric oxidants has been performed. The rate coefficients for the gas-phase reaction of 3-methylfuran with OH and NO3 radicals have been determined at room temperature and atmospheric pressure (air and N2 as bath gases), using a relative method with different experimental techniques. The rate coefficients obtained for these reactions were (in units cm3 molecule−1 s−1) kOH = (1.13 ± 0.22) × 10−10 and kNO3 = (1.26 ± 0.18) × 10−11. Products from the reaction of 3-methylfuran with OH, NO3 and Cl at ...
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Available online: http://dx.doi.org/10.5194/acp-11-3227-2011
A. Tapia ; F. Villanueva ; M.S. Salgado ; B. Cabañas ; E. Martínez ; P. Martín
in Atmospheric Chemistry and Physics (ACP) > Vol. 11. N° 7 [04/01/2011] . - p.3227-3241A study of the kinetics and products obtained from the reactions of 3-methylfuran with the main atmospheric oxidants has been performed. The rate coefficients for the gas-phase reaction of 3-methylfuran with OH and NO3 radicals have been determined at room temperature and atmospheric pressure (air and N2 as bath gases), using a relative method with different experimental techniques. The rate coefficients obtained for these reactions were (in units cm3 molecule−1 s−1) kOH = (1.13 ± 0.22) × 10−10 and kNO3 = (1.26 ± 0.18) × 10−11. Products from the reaction of 3-methylfuran with OH, NO3 and Cl atoms in the absence and in the presence of NO have also been determined. The main reaction products obtained were chlorinated methylfuranones and hydroxy-methylfuranones in the reaction of 3-methylfuran with Cl atoms, 2-methylbutenedial, 3-methyl-2,5-furanodione and hydroxy-methylfuranones in the reaction of 3-methylfuran with OH and NO3 radicals and also nitrated compounds in the reaction with NO3 radicals. The results indicate that, in all cases, the main reaction path is the addition to the double bond of the aromatic ring followed by ring opening in the case of OH and NO3 radicals. The formation of 3-furaldehyde and hydroxy-methylfuranones (in the reactions of 3-methylfuran with Cl atoms and NO3 radicals) confirmed the H-atom abstraction from the methyl group and from the aromatic ring, respectively. This study represents the first product determination for Cl atoms and NO3 radicals in reactions with 3-methylfuran. The reaction mechanisms and atmospheric implications of the reactions under consideration are also discussed.
Language(s): English
Format: Digital (Free)Tags: Aerosols ; Atmosphere ; Environmental degradation ; Research
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Analysis on the impact of aerosol optical depth on surface solar radiation in the Shanghai megacity, China
Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 7. Xu J.; Li C.; Shi H.; et al. - Copernicus GmbH, 2011This study investigated the decadal variation of the direct surface solar radiation (DiSR) and the diffuse surface solar radiation (DfSR) during 1961–2008 in the Shanghai megacity as well as their relationships to Aerosol Optical Depth (AOD) under clear-sky conditions. Three successive periods with unique features of long term variation of DiSR were identified for both clear-sky and all-sky conditions: a "dimming" period from the late 1960s to the mid 1980s, a "stabilization"/"slight brightening" period from the mid 1980s to the mid 1990s, and a "renewed dimming" period thereafter. During the ...
[article]Analysis on the impact of aerosol optical depth on surface solar radiation in the Shanghai megacity, China
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Available online: http://dx.doi.org/10.5194/acp-11-3281-2011
in Atmospheric Chemistry and Physics (ACP) > Vol. 11. N° 7 [04/01/2011] . - p.3281-3289This study investigated the decadal variation of the direct surface solar radiation (DiSR) and the diffuse surface solar radiation (DfSR) during 1961–2008 in the Shanghai megacity as well as their relationships to Aerosol Optical Depth (AOD) under clear-sky conditions. Three successive periods with unique features of long term variation of DiSR were identified for both clear-sky and all-sky conditions: a "dimming" period from the late 1960s to the mid 1980s, a "stabilization"/"slight brightening" period from the mid 1980s to the mid 1990s, and a "renewed dimming" period thereafter. During the two dimming periods of DiSR, DfSR brightened significantly under clear-sky conditions, indicating that change in atmospheric transparency resulting from aerosol emission has an important role on decadal variation of surface solar radiation (SSR) over this area. The analysis on the relationship between the Moderate-resolution Imaging Spectroradiometer (MODIS) retrieved AOD and the corresponding hourly measurements of DiSR and DfSR under clear-sky conditions clearly revealed that AOD is significantly correlated and anti-correlated with DfSR and DiSR, respectively, both above 99% confidence in all seasons, indicating the great impact of aerosols on SSR through absorption and/or scattering in the atmosphere. In addition, both AOD and the corresponding DiSR and DfSR measured during the satellite passage over Shanghai show obvious weekly cycles. On weekends, AOD is lower than the weekly average, corresponding to higher DiSR and lower DfSR, while the opposite pattern was true for weekdays. Less AOD on weekends due to the reduction of transportation and industrial activities results in enhancement of atmospheric transparency under cloud free conditions so as to increase DiSR and decrease DfSR simultaneously. Results show that aerosol loading from the anthropogenic emissions is an important modulator for the long term variation of SSR in Shanghai.
Language(s): English
Format: Digital (Free)Tags: Aerosols ; Impact studies ; Urban zone ; Solar radiation ; Research ; China
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Impact of model grid spacing on regional- and urban- scale air quality predictions of organic aerosol
Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 7. Stroud C.A.; Makar P.A.; Moran M.D.; et al. - Copernicus GmbH, 2011Regional-scale chemical transport model predictions of urban organic aerosol to date tend to be biased low relative to observations, a limitation with important implications for applying such models to human exposure health studies. We used a nested version of Environment Canada's AURAMS model (42- to- 15- to- 2.5-km nested grid spacing) to predict organic aerosol concentrations for a temporal and spatial domain corresponding to the Border Air Quality and Meteorology Study (BAQS-Met), an air-quality field study that took place in the southern Great Lakes region in the summer of 2007. The use o ...
[article]Impact of model grid spacing on regional- and urban- scale air quality predictions of organic aerosol
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Available online: http://dx.doi.org/10.5194/acp-11-3107-2011
C.A. Stroud ; P.A. Makar ; M.D. Moran ; W. Gong ; S. Gong ; J. Zhang ; K. Hayden ; C. Mihele ; J.R. Brook ; J.P.D. Abbatt ; J.G. Slowik
in Atmospheric Chemistry and Physics (ACP) > Vol. 11. N° 7 [04/01/2011] . - p.3107-3118Regional-scale chemical transport model predictions of urban organic aerosol to date tend to be biased low relative to observations, a limitation with important implications for applying such models to human exposure health studies. We used a nested version of Environment Canada's AURAMS model (42- to- 15- to- 2.5-km nested grid spacing) to predict organic aerosol concentrations for a temporal and spatial domain corresponding to the Border Air Quality and Meteorology Study (BAQS-Met), an air-quality field study that took place in the southern Great Lakes region in the summer of 2007. The use of three different horizontal grid spacings allowed the influence of this parameter to be examined. A domain-wide average for the 2.5-km domain and a matching 15-km subdomain yielded very similar organic aerosol averages (4.8 vs. 4.3 μg m−3, respectively). On regional scales, secondary organic aerosol dominated the organic aerosol composition and was adequately resolved by the 15-km model simulation. However, the shape of the organic aerosol concentration histogram for the Windsor urban station improved for the 2.5-km simulation relative to those from the 42- and 15-km simulations. The model histograms for the Bear Creek and Harrow rural stations were also improved in the high concentration "tail" region. As well the highest-resolution model results captured the midday 4 July organic-aerosol plume at Bear Creek with very good temporal correlation. These results suggest that accurate simulation of urban and large industrial plumes in the Great Lakes region requires the use of a high-resolution model in order to represent urban primary organic aerosol emissions, urban VOC emissions, and the secondary organic aerosol production rates properly. The positive feedback between the secondary organic aerosol production rate and existing organic mass concentration is also represented more accurately with the highest-resolution model. Not being able to capture these finer-scale features may partly explain the consistent negative bias reported in the literature when urban-scale organic aerosol evaluations are made using coarser-scale chemical transport models.
Language(s): English
Format: Digital (Free)Tags: Aerosols ; Methodology ; Urban zone ; Weather forecasting ; Air quality ; Research
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Pseudo steady states of HONO measured in the nocturnal marine boundary layer: a conceptual model for HONO formation on aqueous surfaces
Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 7. Wojtal P.; Halla J.D.; McLaren R. - Copernicus GmbH, 2011A complete understanding of the formation mechanism of nitrous acid (HONO) in the ambient atmosphere is complicated by a lack of understanding of processes occurring when aqueous water is present. We report nocturnal measurements of HONO, SO2 and NO2 by differential optical absorption spectroscopy over the ocean surface in a polluted marine environment. In this aqueous environment, we observed reproducible pseudo steady states (PSS) of HONO every night, that are fully formed shortly after sunset, much faster than seen in urban environments. During the PSS period, HONO is constant with time, in ...
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New particle formation events in semi-clean South African savannah
Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 7. Vakkari V.; Laakso H.; Kulmala M.; et al. - Copernicus GmbH, 2011This study is based on 18 months (20 July 2006–5 February 2008) of continuous measurements of aerosol particle size distributions, air ion size distributions, trace gas concentrations and basic meteorology in a semi-clean savannah environment in Republic of South Africa. New particle formation and growth was observed on 69% of the days and bursts of non-growing ions/sub-10 nm particles on additional 14% of the days. This new particle formation frequency is the highest reported from boundary layer so far. Also the new particle formation and growth rates were among the highest reported in the li ...
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Characteristics, sources, and transport of aerosols measured in spring 2008 during the aerosol, radiation, and cloud processes affecting Arctic Climate (ARCPAC) Project
Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 3. Brock C.A.; Cozic J.; Bahreini R.; et al. - Copernicus GmbH, 2011We present an overview of the background, scientific goals, and execution of the Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC) project of April 2008. We then summarize airborne measurements, made in the troposphere of the Alaskan Arctic, of aerosol particle size distributions, composition, and optical properties and discuss the sources and transport of the aerosols. The aerosol data were grouped into four categories based on gas-phase composition. First, the background troposphere contained a relatively diffuse, sulfate-rich aerosol extending from the top of the sea ...
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Impact of deep convection and dehydration on bromine loading in the upper troposphere and lower stratosphere
Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 3. Aschmann J.; Sinnhuber B.-M.; Chipperfield M.P.; et al. - Copernicus GmbH, 2011Stratospheric bromine loading due to very short-lived substances is investigated with a three-dimensional chemical transport model over a period of 21 years using meteorological input data from the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis from 1989 to the end of 2009. Within this framework we analyze the impact of dehydration and deep convection on the amount of stratospheric bromine using an idealized and a detailed full chemistry approach. We model the two most important brominated short-lived substances, bromoform (CHBr3) and dibromomethane (CH2Br2), assumin ...
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Evaluating the effects of microphysical complexity in idealised simulations of trade wind cumulus using the Factorial Method
Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 3. Dearden C.; Connolly P.J.; Choularton T.W.; et al. - Copernicus GmbH, 2011The effect of microphysical and environmental factors on the development of precipitation in warm idealised cloud is explored using a kinematic modelling framework. A simple one-dimensional column model is used to drive a suite of microphysics schemes including a flexible multi-moment bulk scheme (including both single and dual moment cloud liquid water) and a state-of-the-art bin-resolved scheme with explicit treatments of liquid and aerosol. The Factorial Method is employed to quantify and compare the sensitivities of each scheme under a set of controlled conditions, in order to isolate the ...
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Scale-by-scale analysis of probability distributions for global MODIS-AQUA cloud properties: how the large scale signature of turbulence may impact statistical analyses of clouds
Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 3. de la Torre Juárez M.; Davis A.B.; Fetzer E.J. - Copernicus GmbH, 2011Means, standard deviations, homogeneity parameters used in models based on their ratio, and the probability distribution functions (PDFs) of cloud properties from the MODerate resolution Infrared Spectrometer (MODIS) are estimated globally as function of averaging scale varying from 5 to 500 km. The properties – cloud fraction, droplet effective radius, and liquid water path – all matter for cloud-climate uncertainty quantification and reduction efforts. Global means and standard deviations are confirmed to change with scale. For the range of scales considered, global means vary only within 3% ...
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Evaluating a 3-D transport model of atmospheric CO2 using ground-based, aircraft, and space-borne data
Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 3. Feng L.; Palmer P.I.; Yang Y.; et al. - Copernicus GmbH, 2011We evaluate the GEOS-Chem atmospheric transport model (v8-02-01) of CO2 over 2003–2006, driven by GEOS-4 and GEOS-5 meteorology from the NASA Goddard Global Modeling and Assimilation Office, using surface, aircraft and space-borne concentration measurements of CO2. We use an established ensemble Kalman Filter to estimate a posteriori biospheric+biomass burning (BS + BB) and oceanic (OC) CO2 fluxes from 22 geographical regions, following the TransCom-3 protocol, using boundary layer CO2 data from a subset of GLOBALVIEW surface sites. Global annual net BS + BB + OC CO2 fluxes over 2004–2006 for ...
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Sensitivity of mesoscale model urban boundary layer meteorology to the scale of urban representation
Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 3. Flagg D.D.; Taylor P.A. - Copernicus GmbH, 2011Mesoscale modeling of the urban boundary layer requires careful parameterization of the surface due to its heterogeneous morphology. Model estimated meteorological quantities, including the surface energy budget and canopy layer variables, will respond accordingly to the scale of representation. This study examines the sensitivity of the surface energy balance, canopy layer and boundary layer meteorology to the scale of urban surface representation in a real urban area (Detroit-Windsor (USA-Canada)) during several dry, cloud-free summer periods. The model used is the Weather Research and Forec ...
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Characteristics of CALIOP attenuated backscatter noise: implication for cloud/aerosol detection
Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 3. Wu D.L.; Chae J.H.; Lambert A.; et al. - Copernicus GmbH, 2011A research algorithm is developed for noise evaluation and feature detection of the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) Level 1 (L1) backscatter data with an emphasis on cloud/aerosol features in the upper troposphere and lower stratosphere (UT/LS). CALIOP measurement noise of the version v2.01 and v2.02 L1 backscatter data aggregated to (5 km) horizontal resolution is analyzed with two approaches in this study. One is to compare the observed and modeled molecular scatter profiles by scaling the modeled profile (with a fitted scaling factor α) to the observed clear-sky ba ...
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Cloud condensation nuclei in polluted air and biomass burning smoke near the mega-city Guangzhou, China – Part 2: Size-resolved aerosol chemical composition, diurnal cycles, and externally mixed weakly CCN-active soot particles
Atmospheric Chemistry and Physics (ACP), Vol. 11. N° 3. Rose D.; Gunthe S.S.; Su H.; et al. - Copernicus GmbH, 2011Size-resolved chemical composition, mixing state, and cloud condensation nucleus (CCN) activity of aerosol particles in polluted mega-city air and biomass burning smoke were measured during the PRIDE-PRD2006 campaign near Guangzhou, China, using an aerosol mass spectrometer (AMS), a volatility tandem differential mobility analyzer (VTDMA), and a continuous-flow CCN counter (DMT-CCNC).
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