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Atmospheric Environment (v.45, #33)
Diagnostic analysis of ozone concentrations simulated by two regional-scale air quality models by Jerold A. Herwehe; Tanya L. Otte; Rohit Mathur; S. Trivikrama Rao (pp. 5957-5969).
Since the Community Multiscale Air Quality modeling system (CMAQ) and the Weather Research and Forecasting with Chemistry model (WRF/Chem) use different approaches to simulate the interaction of meteorology and chemistry, this study compares the CMAQ and WRF/Chem air quality simulation results for a month-long retrospective study period (August 2006) over the eastern United States, including comparisons with data from several observation networks. To help improve the comparability of the two models, the 2005 Carbon Bond chemical mechanism (CB05) was implemented into WRF/Chem. In addition, the same emissions, initial and boundary conditions have been used in both models to inter-compare simulated ozone (O3) from the WRF-driven CMAQ and WRF/Chem models. Results reveal that ground-level O3 from both models is biased high, especially in the central South and Ohio River Valley; however, WRF/Chem predicts roughly 10% more O3 aloft (1000–2500m AGL) than CMAQ. Different model configurations due to the choice of land surface model (LSM), planetary boundary layer (PBL) physics scheme, and convective cloud parameterization contributed to the differences seen in simulated O3, but most important were the different treatments of the radiative effects of clouds by their respective photolysis schemes.► We compared ozone predictions from two air quality models for a summer month. ► Each model used same chemical mechanism, emissions, initial and boundary conditions. ► Both models overestimate surface ozone, mainly in the South and Ohio River Valley. ► WRF/Chem generally predicts more ozone than WRF-driven CMAQ. ► Boundary layer and photolysis schemes are big factors in modeled ozone differences.
Keywords: CMAQ; WRF/Chem; Ozone; Air quality model; Model evaluation; Model intercomparison
Validation of MODIS aerosol optical depth product over China using CARSNET measurements by Yong Xie; Yan Zhang; Xiaoxiong Xiong; John J. Qu; Huizheng Che (pp. 5970-5978).
This study evaluates Moderate Resolution Imaging Spectroradiometer (MODIS) Aerosol Optical Depth (AOD) retrievals with ground measurements collected by the China Aerosol Remote Sensing NETwork (CARSNET). In current stage, the MODIS Collection 5 (C5) AODs are retrieved by two distinct algorithms: the Dark Target (DT) and the Deep Blue (DB). The CARSNET AODs are derived with measurements of Cimel Electronique CE-318, the same instrument deployed by the AEROsol Robotic Network (AEROENT). The collocation is performed by matching each MODIS AOD pixel (10 × 10 km2) to CARSNET AOD mean within 7.5 min of satellite overpass. Four-year comparisons (2005–2008) of MODIS/CARSNET at ten sites show the performance of MODIS AOD retrieval is highly dependent on the underlying land surface. The MODIS DT AODs are on average lower than the CARSNET AODs by 6–30% over forest and grassland areas, but can be higher by up to 54% over urban area and 95% over desert-like area. More than 50% of the MODIS DT AODs fall within the expected error envelope over forest and grassland areas. The MODIS DT tends to overestimate for small AOD at urban area. At high vegetated area it underestimates for small AOD and overestimates for large AOD. Generally, its quality reduces with the decreasing AOD value. The MODIS DB is capable of retrieving AOD over desert but with a significant underestimation at CARSNET sites. The best retrieval of the MODIS DB is over grassland area with about 70% retrievals within the expected error. The uncertainties of MODIS AOD retrieval from spatial–temporal collocation and instrument calibration are discussed briefly.► MODIS C5 AODs from both DT approach and DB approach were evaluated over China. ► The evaluation is based on the 4-year ground-based measurements from Chinese CARSNET. ► MODIS AOD retrievals are dependent upon underlying land surface and the season. ► Surface reflectance and aerosol assumption can impact MODIS AOD over China obviously.
Keywords: MODIS; CARSNET; Aerosol optical depth; Validation; China
Atmospheric aerosol monitoring as a strategy for the preventive conservation of urban monumental heritage: The Florence Baptistery by N. Ghedini; I. Ozga; A. Bonazza; M. Dilillo; H. Cachier; C. Sabbioni (pp. 5979-5987).
The over time a knowledge of atmospheric aerosol composition near monuments has become an increasingly important issue in preservation strategies. Concerning the protection of outdoor monumental heritage against urban air pollution, scientific works have mainly focused on the composition of background urban aerosol. In the literature the importance of atmospheric pollutant monitoring close to monuments is not yet sufficiently emphasized. In order to fill this gap, the atmosphere in proximity of the Florence Baptistery was monitored throughout 2003. Aerosol samples were collected close to two of the three doors, characterized by different exposures to pollutant sources. The non-carbonate carbon and soluble ions in the total suspended matter were measured. The paper presents and discusses the comparison between the analytical data obtained from the different sampling sites on the same monument. The results obtained may provide a contribution to the formulation of guidelines for a suitable safeguard of cultural heritage.► Aerosol monitoring near monument adopted as preventive conservation strategy. ► Close to the Florence Baptistery TSP was continuously monitored throughout 2003. ► The results show different aerosol composition nearby the two Baptistery doors. ► Non-carbonate carbon at Northern door is almost always higher than at Southern one. ► Protection of cultural heritage constitutes a priority for all countries.
Keywords: Cultural heritage; Outdoor aerosol monitoring; Urban area; Non-carbonate carbon; Ions
Study of geographical trends of polycyclic aromatic hydrocarbons using pine needles by José Manuel Amigo; Nuno Ratola; Arminda Alves (pp. 5988-5996).
In this work, pine needles were used as polycyclic aromatic hydrocarbons (PAHs) markers to study the PAHs distribution over several geographical locations in Portugal and over time. Four pine needle sampling campaigns (winter, spring, summer and autumn 2007) were carried out in 29 sites, covering the major urban centres, some industrial points, smaller cities, rural areas and remote locations. Needles from Pinus pinaster Ait. and Pinus pinea L. trees were collected from 2005 and 2006 shoots, corresponding to one up to three years of exposure. Spatial trends of the incidence of PAHs indicate an increase from the remote to the urban and industrial sites. The mean values for the sum of 16 PAHs ranged from 96±30ngg−1 (dry weight) for remote sites to 866±304ngg−1 (dw) for industrial sites for P. pinaster needles and from 188±117ngg−1 (dw) for rural sites to 337±153ngg−1 (dw) for urban sites for P. pinea. Geographic information system tools and principal component analysis revealed that the contamination patterns of PAHs are somehow related to several socio-geographic parameters of the sampling sites. The geographical trend for the PAHs is similar between seasons in terms of PAH levels, but some diverse behaviour is found on the separation of lighter and heavier PAHs. Differences between P. pinaster and P. pinea needles are stronger in terms of PAH uptake loads than in the site type fingerprints.► Considerable difference between areas has been found in the distribution of PAHs. ► Contamination patterns of PAHs are related to several socio-geographic parameters. ► The geographical trend for PAHs levels is similar between seasons. ► Diverse behaviour is found on the separation of lighter and heavier PAHs.
Keywords: Polycyclic aromatic hydrocarbons; Pine needles; Spatial trends; Geographic information system; Principal component analysis
The heterogeneous photo-oxidation of difenoconazole in the atmosphere by M. Al Rashidi; O. El Mouden; A. Chakir; E. Roth; R. Salghi (pp. 5997-6003).
A photo-chemical reactor coupled to a UV spectrometer was used to investigate the degradation of difenoconazole deposited on a quartz surface by atmospheric oxidants, namely ozone and OH radicals. OH-oxidation experiments were conducted relative to a reference compound, the terbuthylazine. The rate constant of heterogeneous OH-oxidation of difenoconazole was found to be (7.1 ± 0.8) 10−14 cm3 molecule−1 s−1. Meanwhile, ozone oxidation experiments were performed in the absolute mode and were interpreted by both, the Langmuir–Rideal (LR) and the Langmuir-Hinshelwood (LH) models of heterogeneous reactions. In the case of ozonolysis, a comparison between both models shows that, within the range of ozone concentration employed in this study, both models fit the experimental data correctly. The obtained results show that the atmospheric life-time of difenoconazole with respect to both oxidants is in the order of several months, meaning that this pesticide is relatively persistent, and may be transported over long distances.► Heterogeneous reactivity. ► LH and LR models. ► Atmospheric life-time.
Keywords: Pesticide; Difenoconazole; Kinetics; Life-time; Atmospheric degradation; Heterogeneous reaction
Aerosol optical properties at Mt. Waliguan Observatory, China by Huizheng Che; Yaqiang Wang; Junying Sun (pp. 6004-6009).
Aerosol optical properties at the Mt. Waliguan Observatory (WLG) in Northwest China are investigated based on the measurements of aerosol optical depth (AOD) at 500nm and Angstrom exponent ( α) from September 2009 to August 2010. Mean values of 0.14±0.07 and 0.59±0.24 are observed for AOD and Angstrom exponent, respectively, both of which are characterized by a wide range of values from 0.02 to 1.13 and −0.03 to 1.37, respectively. A seasonal variation is found with high AOD and low Angstrom exponent values in spring which could be attributed to the effect of Asian dust events, and low ground AOD level of less than 0.10 in autumn and winter. The k-means cluster analysis separates the measurements into three aerosol modes based on the AOD and Angstrom exponent distributions with the frequency distribution of AOD centering about 0.07±0.002, 0.11±0.02, and 0.18±0.12. AOD at WLG is significantly larger than those at Mauna Loa (MLO) and Izana (IZA) because of the contribution of the dust aerosol in spring from desert regions of Western China and fine particles transport from Central China in summer. In addition, the factors of nearby surface, geographic location and different aerosol components could also contribute to higher AOD at WLG than MLO and IZA.► Aerosol optical properties at the Mt. Waliguan Observatory were analyzed. ► Aerosol optical parameters at Mt. Waliguan show an obvious seasonal variability. ► AOD at Mt. WLG is obviously larger than MLO and IZA global observatories. ► Mineral and anthropogenic particles can affect aerosol optical properties of Mt. WLG.
Keywords: Aerosol optical depth; Angstrom exponent; Sunphotometer; Mt. Waliguan Observatory; China
Trends in the characteristics of allergenic pollen circulation in central Europe based on the example of Szeged, Hungary by László Makra; István Matyasovszky; Áron József Deák (pp. 6010-6018).
The aim of the study is to analyse trends of the pollination season with its start and end dates, as well as trends of the annual total pollen count and annual peak pollen concentration for the Szeged agglomeration in Southern Hungary. The data set covers an 11-year period (1999–2009) and includes one of the largest spectra, with 19 taxa, as well as seven meteorological variables (minimum-, maximum- and mean temperature, total radiation, relative humidity, rainfall and wind speed). For highly skewed data, such as the annual total number of pollen counts or annual peak pollen concentrations, the Mann–Kendall test has a substantially greater predictive power than the t-test. After performing Mann–Kendall tests, the annual cycles of daily slopes of pollen concentration trends and annual cycles of daily slopes of climate variable trends are calculated. This kind of trend analysis is a novel approach as it provides information on annual cycles of trends. In order to represent the strength of their relationships an association measure (AM) and a multiple association measure (MAM) are introduced. Based on climate sensitivity, the individual taxa are sorted into three categories. The results obtained for the pollen quantity and phenological characteristics are compared with two novel climate change related categories, namely risk and expansion potential due to the climate change for each taxon. The total annual pollen count and annual peak pollen concentrations indicate a small number of changes when using ordinary linear trends, while the total annual pollen count calculated via daily linear trends show significant trends (70% of them positive) for almost all taxa. However, except for Poaceae and Urtica, there is no significant change in the duration of the pollination season. The association measure performs well compared to the climate change related forces. Furthermore, remarkable changes in pollen season characteristics are also in accordance with the risk and expansion potential due to climate change.► Daily trend analysis is a novel approach and informs on annual cycles of trends. ► Risk and expansion potential due to the climate change are novel categories. ► The total annual pollen count computed via daily linear trends show important trends. ► The association measure corresponds with the climate change related forces. ► Notable changes in pollen parameters agree with the climate change related forces.
Keywords: Pollen; Pollination season; Trend; Climate change; Respiratory allergy
Impact of scaling and body movement on contaminant transport in airliner cabins by Sagnik Mazumdar; Stephane B. Poussou; Chao-Hsin Lin; Sastry S. Isukapalli; Michael W. Plesniak; Qingyan Chen (pp. 6019-6028).
Studies of contaminant transport have been conducted using small-scale models. This investigation used validated Computational Fluid Dynamics (CFD) to examine if a small-scale water model could reveal the same contaminant transport characteristics as a full-scale airliner cabin. But due to similarity problems and the difficulty of scaling the geometry, a perfect scale up from a small water model to an actual air model was found to be impossible. The study also found that the seats and passengers tended to obstruct the lateral transport of the contaminants and confine their spread to the aisle of the cabin. The movement of a crew member or a passenger could carry a contaminant in its wake to as many rows as the crew member or passenger passed. This could be the reason why a SARS infected passenger could infect fellow passengers who were seated seven rows away. To accurately simulate the contaminant transport, the shape of the moving body should be a human-like model.► The small-scale water model did not work in the same way as the full-scale air model. ► CFD models have no scaling issues. ► A walking person can carry a contaminant from its source to very far away. ► The body movement could cause transmission of the SARS pathogen from the infected passenger to those seated far away in Flight 112 in 2003.
Keywords: CFD; Contaminant transport; Aircraft cabin; Moving body; Dynamic grids; SARS
Evaluating management effects on nitrous oxide emissions from grasslands using the process-based DeNitrification–DeComposition (DNDC) model by Rashad Rafique; Matthias Peichl; Deirdre Hennessy; Gerard Kiely (pp. 6029-6039).
The development of agricultural mitigation strategies to reduce greenhouse gas (GHG) emissions is urgent in the context of climate change – land use interactions. In this study the DNDC biogeochemical model was used to study nitrous oxide (N2O) emissions from grazed grasslands in southern Ireland. The objectives of this study were: (1) to evaluate the DNDC model using a two year (2008–2009) data set of chamber measured N2O fluxes at eight grassland sites and (2) to investigate the impact of different management scenarios on N2O emissions including changes in i) inorganic nitrogen (N) fertilizer application rates ii) slurry application rates; and iii) animal density (livestock unit per hectare LU ha−1). The comparison of modeled daily DNDC fluxes (using a combination of measured and default soil parameters) and measured fluxes resulted in an r (coefficient correlation) = 0.48. To improve the model performance, the fluxes for 2008 were used in a calibration exercise during which the soil properties were optimized to obtain the best fit of N2O fluxes. This resulted in an improved model performance, with an r = 0.62. In a validation exercise using 2009 data, we used the model parameters set (e.g. soils) from the calibration exercise and this resulted in a model performance with an r = 0.57. The annual N2O fluxes (measured and modeled) were appreciably higher than those estimated using the IPCC emissions factor of 1.25%. In scenario analysis, the modeled N2O fluxes only increased/decreased on average ±6% and ±7% following a 50% increase/decrease of inorganic N and slurry N applications respectively. These modeled scenario % changes are much lower than the IPCC emission factor % changes of a 50% increase in N2O emissions for a 50% increase in nitrogen applied. An absolute change scenario (±50 kg) in inorganic N and slurry N resulted in greater change in N2O fluxes (±9% inorganic N and ±17% slurry N) as compared to the relative change scenario (above). Furthermore, DNDC N2O flux estimates were not sensitive to changes in animal density (LU ha−1). The latter is a scenario limitation in the current model version. This study suggests that the calibration of soil parameters for Irish conditions is necessary for optimum simulation with DNDC and highlights the potential of management strategies for reducing N2O emissions from grazed grasslands. It further highlights the difference between DNDC and IPCC estimates that require further research.► DNDC model was used for N2O estimation and management scenarios in grasslands. ► DNDC captured the general trend and annual N2O fluxes after calibration of soil parameters. ► In scenario DNDC showed lower response with nitrogen input and no response to animal density. ► This poor response is not inline with IPCC prediction which indicate limitation of DNDC. ► We conclude DNDC may underestimate the N2O fluxes which need further research.
Keywords: DNDC; Calibration; Validation; N input; Slurry application; Livestock unit
Filterable water-soluble organic nitrogen in fine particles over the southeastern USA during summer by Neeraj Rastogi; Xiaolu Zhang; Eric S. Edgerton; Ellery Ingall; Rodney J. Weber (pp. 6040-6047).
Time integrated high-volume PM2.5 samples were collected separately during day and night from 1 August to 10 September 2008 at a paired urban (Atlanta)-rural (Yorkville) sites as part of the August Mini-Intensive Gas and Aerosol Study (AMIGAS). Selected filters ( n=96, 48 for each site) were analyzed for a suite of water-soluble chemical species, including major inorganic ions, water-soluble organic carbon (WSOC), water-soluble total and inorganic nitrogen (WSTN and WSIN), and levoglucosan. Semi-continuous analyses of PM2.5 mass, soluble ions, WSOC, and gaseous O3, SO2, NO, NO2, NOy, CO, and meteorological parameters were also carried out in parallel. This study focuses on the characteristics of filterable water-soluble organic nitrogen (WSON), estimated by the difference in the measured concentrations of WSTN and WSIN, determined from aqueous filter extracts. At both sites, WSON varied from below the limit of detection (25ng-Nm−3) to ∼600ng-Nm−3 and on average contributed ∼10% to WSTN mass, with the majority of soluble nitrogen being ammonium (∼82%). WSON:WSOC (or N:C) mass ratios ranged between 0 and 27% at both the sites with a median value of ∼5%, similar to what has been reported in another study in the southeastern USA. At both the urban and rural sites median nighttime levels of WSON and N:C were observed to be consistently higher than daytime values. Based on correlation analyses, daytime WSON sources appeared different than nighttime sources, especially at the urban site. Overall, the data suggest the importance of coal-combustion (e.g., link to SO2), vehicle emissions, soil dust and biomass burning as WSON sources, and that nitrogenous organic compounds are likely a fairly small fraction of the secondary organic aerosol for this location during summer.► Characteristics of WSON in aerosols over southeast USA were studied over urban and rural site. ► Multiple sources contribute to WSON over both sites. ► Nighttime WSON concentrations were higher than those during daytime. ► Nitrogenous organics were not a substantial fraction of SOA at our study sites.
Keywords: WSON; Aerosols; Diurnal variation; AMIGAS; WSON:WSOC ratio; Organic nitrogen
Semi-continuous measurement of water-soluble ions in PM2.5 in Jinan, China: Temporal variations and source apportionments by Xiaomei Gao; Lingxiao Yang; Shuhui Cheng; Rui Gao; Yang Zhou; Likun Xue; Youping Shou; Jing Wang; Xinfeng Wang; Wei Nie; Pengju Xu; Wenxing Wang (pp. 6048-6056).
To better understand secondary aerosol pollution and potential source regions, semi-continuous measurement of water-soluble ions in PM2.5 was performed from December 2007 to October 2008 in Jinan, the capital of Shandong Province. The data was analyzed with the aid of backward trajectory cluster analysis in conjunction with redistributed concentration field (RCF) model and principal component analysis (PCA).SO42−,NO3− andNH4+ were the most abundant ionic species with annual mean concentrations (±standard deviations) of 38.33 (±26.20), 15.77 (±12.06) and 21.26 (±16.28) μg m−3, respectively, which are among the highest levels reported in the literatures in the world. Well-defined seasonal and diurnal patterns ofSO42−,NO3− andNH4+ were observed. The fine sulfate and nitrate oxidation ratios (SOR and NOR) were much higher in summer (SOR: 0.47 ± 0.13; NOR: 0.28 ± 0.03) than those in other seasons (SOR: 0.17–0.30; NOR: 0.12–0.14), indicating more extensive formations ofSO42− andNO3− in summer. The most frequent air masses connected with high concentrations ofSO42−,NO3− andNH4+ originated from Shandong Province in spring, autumn and winter, while from the Yellow Sea in summer, and then slowly traveled in Shandong Province to Jinan. RCF model indicated that Shandong Province was the main potential source region forSO42− andNO3− and other potential source regions were also identified including the provinces of Hebei, Henan, Anhui and Jiangsu and the Yellow Sea. Principal component analysis indicated that the major sources contributing to PM2.5 pollution were secondary aerosols, coal/biomass burnings and traffic emissions.► Semi-continuous measurement of water-soluble ions in PM2.5 was conducted in Jinan. ► The annual meanSO42−,NO3− andNH4+ concentrations were almost highest in the literatures in the world. ► The obvious seasonal and diurnal variations were related with local emissions and meteorological conditions. ► The seasonal transport patterns and potential source regions of secondary ions were identified. ► Secondary aerosols, coal/biomass burnings and traffic emissions were the major sources of PM2.5.
Keywords: semi-continuous; Water-soluble ions; PM; 2.5; Seasonal and diurnal variations; Transport patterns; Sources; Jinan
Validation of modeled carbon-dioxide emissions from an urban neighborhood with direct eddy-covariance measurements by A. Christen; N.C. Coops; B.R. Crawford; R. Kellett; K.N. Liss; I. Olchovski; T.R. Tooke; M. van der Laan; J.A. Voogt (pp. 6057-6069).
Modeled carbon-dioxide (CO2) emissions from an urban area are validated against direct eddy-covariance flux measurements. Detailed maps of modeled local carbon-dioxide emissions for a 4 km2 residential neighborhood in Vancouver, BC, Canada are produced. Inputs to the emission model include urban object classifications (buildings, trees, land-cover) automatically derived from Light Detection and Ranging (LiDAR) and optical remote sensing in combination with census, assessment, traffic and measured radiation and climate data. Different sub-models for buildings, transportation, human respiration, soils and vegetation were aggregated. Annual and monthly CO2 emissions were modeled on a spatial grid of 50 m for the entire study area. The study area overlaps with the source area of a micrometeorological flux tower for which continuous CO2 flux data (net exchange) were available for a two-year period. The measured annual total was 6.71 kg C m−2 yr−1with significant seasonal differences (16.0 g C m−2 day−1 in Aug vs. 22.1 g C m−2 day−1 in Dec correlated with the demand for space heating) and weekday-weekend differences (25% lower emissions on weekends attributed to traffic volume differences). Model results were weighted using the long-term turbulent source areas of the tower. Annual total modeled (7.42 kg C m−2 yr−1) and measured emissions agreed within 11%, but show more substantial differences in wind sectors dominated by traffic emissions. Over the year, agreement was better in summer (5% overestimation by model) vs. winter (15% overestimation), which is partially attributed to climate differences unaccounted for in the building energy models. The study shows that direct CO2 flux measurements based on the EC approach - if sites are carefully chosen - are a promising method to validate fine-scale emission inventories/models at the block or neighborhood scale and can inform further model improvements.► Detailed maps of local carbon-dioxide emissions were modeled for a 4 km2 urban area. ► Maps are compared to two full years of direct eddy-covariance (EC) measurements on a tower. ► Modeled annual total carbon emissions agree within 11% with tower measurements. ► Higher differences found in sectors with arterial roads and during heating-period. ► EC measurements are a promising method to validate spatial emission inventories.
Keywords: GHG emission modeling; Building energy modeling; Carbon-dioxide; Flux measurements; Eddy-covariance; LiDAR; Model validation
Potential contribution of new particle formation to cloud condensation nuclei in Beijing by D.L. Yue; M. Hu; R.Y. Zhang; Z.J. Wu; H. Su; Z.B. Wang; J.F. Peng; L.Y. He; X.F. Huang; Y.G. Gong; A. Wiedensohler (pp. 6070-6077).
New particle formation (NPF) events have been recognized as an important process contributing to the cloud condensation nuclei (CCN) formation. In this study, measurement of NPF and predicted number concentrations of CCN using κ-Köhler theory were analyzed to assess the contribution of NPF to possible CCN. The particle growth rates of NPF events were categorized to two types: sulfur-rich (condensation and neutralization of sulfuric acid dominating net growth rate) and sulfur-poor cases. The growth rates for the sulfur-poor events were about 80% larger than those of the sulfur-rich cases on average. NPF events increased the CCN number concentrations by 0.4–6 times in the megacity area of Beijing. The enhancement ratios (the ratio of CCN number concentrations when obvious particle growth ended to that when it started during NPF events) were high for large supersaturation ( S). For example, it was about 30–50% higher under S = 0.86% than under S = 0.07%. The enhancement ratios exhibited similar seasonal variation as the growth rates with a larger value in summer than other seasons, which suggested that growth rate was a key factor in the conversion of NPF to possible CCN. The enhancement ratios were higher during the sulfur-poor NPF events with larger growth rates mainly contributed by organic species, indicating that organic species were the dominant chemical contributor in facilitating the conversion of newly formed particles to possible CCN in the Beijing Megacity.► New particle formation (NPF) and fine particle chemical composition were measured. ► CCN number concentrations were predicted using κ-Köhler theory. ► NPF events increase the CCN number concentrations by 0.4–6 times. ► Growth rate is the key factor in the conversion of NPF to possible CCN. ► Organic species are implicated as the dominant contributor in the CCN conversion.
Keywords: New particle formation; Particle growth; Cloud condensation nuclei; Number concentration
Nocturnal ozone enhancement in the lower troposphere observed by lidar by Shi Kuang; M.J. Newchurch; John Burris; Lihua Wang; Patrick I. Buckley; Steve Johnson; Kevin Knupp; Guanyu Huang; Dustin Phillips; Wesley Cantrell (pp. 6078-6084).
An ozone enhancement in the nocturnal residual layer was observed by the Huntsville ozone lidar from the late evening to midnight on 4 October 2008. The well-correlated ozone, aerosol, water vapor, and wind structures suggest a low-level jet is responsible for this ozone enhancement. HYSPLIT backward trajectories support this conclusion with southerly transport suggesting Birmingham, AL as the source. Correspondingly, the higher increasing rate of surface ozone observed in the morning of 5 October can be explained by the entrainment into the mixed layer of higher ozone aloft on this day as compared with 4 October. This case study demonstrates the importance of continuous high-resolution lidar profiling for capturing short-duration ozone variations in the lower troposphere.► A nocturnal ozone enhancement was observed associated with a low-level jet. ► This enhancement resulted in a higher increasing rate of the 2nd-day surface ozone. ► However, higher daily-surface maximum ozone was not observed as expected.
Keywords: Air quality; Atmospheric chemistry; DIAL; Huntsville; Nocturnal boundary layer; Residual layer
The Aerodyne Inverse Modeling System (AIMS): Source estimation applied to the FFT 07 experiment and to simulated mobile sensor data by Simón E. Albo; Oluwayemisi O. Oluwole; Richard C. Miake-Lye (pp. 6085-6092).
The Aerodyne Inverse Modeling System was developed to enable location and characterization of hazardous atmospheric releases from dispersion and meteorological data. It combines an automatically-generated tangent-linear of SCIPUFF with a cost function tailored for practical applications and a minimization algorithm that can search for multiple instantaneous or continuous sources without requiring an initial guess. In this work AIMS was applied to estimate the sources in 84 FFT 07 cases that included instantaneous and continuous releases for up to four source locations. FFT 07 was a controlled short-range (∼500 m) dispersion test using 100 digiPIDs evenly distributed over an area of 0.5 × 0.5 km. AIMS estimated sources were in average within 90–150 m of the real sources, with the distances from estimated to real source ranging from 0 to 510 m. AIMS performed better estimating the location of instantaneous sources than of continuous ones. It also performed better for single-source situations than for multiple source scenarios and when 16 sensors were used instead of 4. In addition to using stationary sensors, AIMS also has the capability of processing data from mobile sensors. This was applied using model-generated data in an example of a release in a setting similar to an industrial facility.► Source estimation algorithm does not require an initial guess. ► Data from stationary and mobile sensors can be processed. ► Multiple instantaneous or continuous releases. ► Determines the number of sources, source locations, strengths, release times and durations.
Keywords: Source estimation; Inverse modeling; Source location; Air quality; Emissions modeling; Atmospheric pollution
Biotransformation of methanol and formaldehyde by bacteria isolated from clouds. Comparison with radical chemistry by Slavomíra Husárová; Mickaël Vaïtilingom; Laurent Deguillaume; Mounir Traikia; Virginie Vinatier; Martine Sancelme; Pierre Amato; Mária Matulová; Anne-Marie Delort (pp. 6093-6102).
The kinetics of biodegradation of methanol and formaldehyde in phosphate buffer at pH 7 by 4 bacterial strains ( Pseudomonas spp., Bacillus sp. and Frigoribacterium sp.) isolated from cloud water at the puy de Dôme mountain have been investigated using1H and13C NMR spectroscopy. We showed that biodegradation occurred at 5°C and 17°C, respectively average and summertime temperature considered within the cloud system at this site. They ranged from 10−19 to 10−21mol cell−1s−1 both at 5 and 17°C for formaldehyde, and from 10−21 to 10−23mol cell−1s−1 at 5 and 17°C for methanol. Metabolic intermediates were identified, with notably production of C3 compounds (glycerol, 1,2- and 1,3-propanediol) from formaldehyde by the strain Bacillus sp. In order to evaluate to which extent microbiological oxidation of organic compounds has to be considered as an alternative route to radical chemistry in cloud water, the biodegradation rates measured were compared with rates related to the reactivity of organic species with free radicalsOH (daytime chemistry) and NO3 (nighttime chemistry) under two cloud situations (urban and remote cases). Clearly, measured biological and chemical reaction rates were in the same range of magnitude and their relative contribution varies according to the scenarios we tested, including the temperature of the clouds (5 or 17°C), the category of the clouds (urban and remote) and the diurnal cycle (day and nighttime). Except for the degradation of methanol at 5°C in remote clouds, our results show that biotransformation processes could be the main sink for C1 compounds in liquid clouds ( T≥5°C≡“warm cloud”) during the night and both in polluted and non polluted clouds.► Bacteria are isolated from cloud water collected at the puy de Dôme station. ► They are able to transform methanol and formaldehyde at temperatures typical of real warm clouds. ► Biodegradation rates are in the same range of magnitude than those from radical chemistry. ► Metabolic intermediates with 3 carbons are produced by one of the strains.
Keywords: Cloud; Atmospheric chemistry; Microorganisms; Biodegradation; Radical chemistry; Organic compounds
Mitigation of short-lived heating components may lead to unwanted long-term consequences by Gunnar Myhre; Jan S. Fuglestvedt; Terje K. Berntsen; Marianne T. Lund (pp. 6103-6106).
A mitigation strategy for reducing emissions of short-lived heating components such as black carbon (BC) aerosols and ozone precursors to limit global warming has frequently been suggested (). BC emissions influence the radiative balance in several ways through direct and semi-direct aerosol effects, as well as by impacting the surface albedo (), and their net effect is likely a warming that enhances the total man-made warming. However, the role that BC or other short-lived heating components may play in future mitigation strategies must be formulated with caution to avoid unforeseen and unwanted consequences. A near-term mitigation of short-lived heating components could lead to a delayed action on CO2 and other long-lived greenhouse gases and thus an increased long-term warming. A key element is whether policies are designed as a consequence of predicted warming or observed warming. Without a clear strategy, early BC or ozone reductions may even lead to an unexpectedly larger temperature change.
Keywords: Black carbon; Mitigation strategy; Short-lived components