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Atmospheric Environment (v.45, #38)
A special issue of selected papers from the 7th International Conference on Air Quality – Science and Application, Istanbul, 24–27 March 2009
by Tim Butler Guest Editor; Ranjeet S. Sokhi Guest Editor; Jaakko Kukkonen Guest Editor; Alexander Baklanov Guest Editor; Michael Gauss Guest Editor (pp. 6843-6844).
Integrated modeling for forecasting weather and air quality: A call for fully coupled approaches by Georg Grell; Alexander Baklanov (pp. 6845-6851).
This paper discusses some of the differences between online and offline approaches for both air quality forecasting and numerical weather prediction, and argues in favor of an eventual migration to integrated modeling systems that allow two-way interactions of physical and chemical processes. Recent studies are used that directly compared online and offline simulations to discuss possible shortcomings for both air quality and weather forecasting. The disadvantages of offline approaches are easy to show for air quality forecasting. On the other hand, a positive impact on short to medium range weather forecasts that is significant enough to justify an implementation at operational weather forecasting centers is more difficult to prove, and may initially only come through an improvement of the meteorological data assimilation. Eventually though, a migration to an integrated modeling system will provide new opportunities for weather prediction modelers as well. The simulation of chemical species will allow identification of shortcomings in currently used forecast models as well as lead to better use of meteorological data assimilation.
Keywords: Meteorology; Numerical weather prediction; Air quality forecasting; Chemical weather prediction; Atmospheric chemistry; Aerosols; Clouds; Radiation; Climate; Two-way interactions; Feedback mechanisms; Online integrated air quality – meteorology modeling systems; Atmospheric chemical transport modeling; Chemical data assimilation
Does the resolution of megacity emissions impact large scale ozone? by Øivind Hodnebrog; Frode Stordal; Terje K. Berntsen (pp. 6852-6862).
The importance of using high resolution when modelling the impact of megacity emission on large scale tropospheric ozone has been investigated using the regional WRF-Chem model. Two 3-day summer periods in July and August 2003 have been simulated for three megacities; London, Ruhr, and Cairo. Simulations have been performed with constant model resolution (9 × 9 km2) and with megacity emission resolutions at 9 × 9 km2, 27 × 27 km2, and 81 × 81 km2, by using detailed emission inventories averaged to the appropriate resolution. In order to quantify the megacities’ contributions to regional ozone, simulations without megacity emissions were also performed.In general, results from the six case studies show that the inaccuracies that arise on a large scale when using megacity emission resolution at a typical scale of a global Chemistry-Transport Model (81 × 81 km2) were relatively small (12% or less). However, the impact of resolution on ozone changes caused by megacity emissions depends strongly on meteorological conditions. The case with the largest impact (London, July 2003) showed that net ozone formed from the megacity were 12% higher when using 81 × 81 km2 rather than 9 × 9 km2 emission resolution, due to stronger ozone production since the NOx emissions were more rapidly diluted to regions where the ozone production was NOx limited in the coarse resolution case. Our study suggests that high resolution is more important for local air pollution studies than for large scale ozone changes relevant for climate studies, since a change in megacity emission resolution induces small-scale spatial changes in ozone fields, but relatively small changes when integrating over a large volume. These results indicate that parameterization of megacity emissions in large scale models may be unnecessary. However, the impact of a finer resolution of the meteorology is not studied here and could possibly give larger effects seen from a climate perspective.► Scale interactions in megacity ozone formation studied with WRF-Chem. ► Relatively small ozone changes (<12 %) when changing emission resolution. ► Ozone impact strongly dependent on meteorological conditions. ► High resolution more important for local air pollution than for climate studies.
Keywords: WRF-Chem; Ozone; Scale interaction; Megacities; Emission hot spots
Projection of anthropogenic volatile organic compounds (VOCs) emissions in China for the period 2010–2020 by Wei Wei; Shuxiao Wang; Jiming Hao; Shuiyuan Cheng (pp. 6863-6871).
The future (2010–2020) anthropogenic volatile organic compounds (VOCs) emissions in China were projected in this study using 2005 as the reference year. The projections are based on the assumptions of a lower population growth rate (less than 1%), continuous economic development with high GDP growth, and increased urbanization. The results show that the national VOCs emissions would continuously increase from 19.4 Tg in 2005 to 25.9 Tg in 2020, even if China's legislative standards for VOCs emissions are implemented effectively in the future (assumed as control scenario I). The contributions of various emission sources were found to differ greatly in the period of 2010–2020. Solvent utilization would become the largest contributor rising from 22% to 37%, along with an increase for industrial processes from 17% to 24%. However, road vehicle emissions would rapidly decrease from 25% to 11% due to the strict VOCs emission limit standards in China, along with the decrease for stationary fuel combustion from 23% to 16% caused by the reduction of domestic biofuel consumption. Additionally, there would be a notable divergence among provincial emissions. The developed eastern and coastal regions would emit more VOCs than the relatively underdeveloped western and inland regions. Moreover, this divergence grows in the future.When we assumed stricter control measures for solvent utilization and industrial processes (control scenario II) for that period, the projections revealed national VOCs emissions per year would remain at about 20 Tg, if exhaust after-treatment systems are installed in newly-built factories (after 2005) for the most important industrial sources, and the market shares of “low/zero-VOCs” products in paints, adhesives and printing ink raise to the present levels of developed countries. The emission abatements of the two types of measures were estimated to be similar. While scenario II indicates that the sectoral and provincial differences of VOCs emissions would still exist, they would be smaller than in scenario I.► This study projected the future (2010-2020) anthropogenic VOCs emissions in China. ► A continuous increase was forecasted, from 19.4 Tg in 2005 to 25.9 Tg in 2020, when China's pertinent legislative standards are implemented effectively. ► If more advanced control measures designed, the future annual VOCs emissions would remain at about 20 Tg. ► In both scenarios, contributions of emission sources would notably change, solvent utilization and industrial processes becoming the biggest contributors. ► The prominent discrepancies in spatial emissions would become larger with time.
Keywords: VOCs; Emission inventory; Projection; China
Long-term trends of primary and secondary NO2 production in the Athens area. Variation of the NO2/NOx ratio by I. Mavroidis; A. Chaloulakou (pp. 6872-6879).
This paper examines the contribution of primary and secondary NO2 production in NOx concentrations and offers a comprehensive analysis of the long-term trends of NOx, NO2 and O3 concentrations, as well as of the NO2/NOx ratio, in the Athens urban conurbation. Long-term pollutant concentration time series show that NO2 concentrations in Athens have decreased since 1987 but at a slower rate than those of NOx, resulting to an increasing NO2/NOx concentration ratio. However, this increasing trend is much smaller than those observed in urban areas of other European countries. The possible causes of this trend are examined and especially the interaction with ozone and the amount of direct NO2 traffic emissions. The results indicate that the increasing NO2/NOx ratio in the Athens area is mainly attributable to an increased secondary formation of NO2 through photochemical reactions in the atmosphere. More specifically, two different empirical methodologies were applied to examine the primary NO2 concentration fraction in Athens, using ambient monitoring data from a kerbside station. Both methods indicate that the primary NO2 concentration share has not altered significantly between 1998 and 2006. This is mainly attributed to the fact that in the Athens area diesel passenger cars are not allowed and after-treatment technologies such as particle filters and oxidation catalysts are not yet applied in Greece. A probable future penetration of diesel passenger cars in Athens should be combined with inventories of primary NO2 emissions and with the development of appropriate policies to reduce ambient NO2 concentrations below the EU limit values.► The NO2/NOx concentration ratio in Athens is increasing slowly since 1990. ► The primary NO2 concentration share in Athens has not altered notably with time. ► The behaviour of primary NO2 is due to diesel passenger cars not allowed in Athens. ► The NO2/NOx trend in Athens is attributable to increased secondary NO2 formation.
Keywords: Traffic-related air pollutants; NOx emissions reduction; NO; 2; air quality standards; NO; 2; /NOx ratio; Photochemical oxidant; Primary NO; 2; Diesel exhaust after-treatment
Mechanisms responsible for the build-up of ozone over South East England during the August 2003 heatwave by X.V. Francis; C. Chemel; R.S. Sokhi; E.G. Norton; H.M.A. Ricketts; B.E.A. Fisher (pp. 6880-6890).
The Community Multiscale Air Quality (CMAQ) model is used in order to quantify reasons for the build-up of ozone over South East England during the August 2003 heatwave. Unlike previous studies, the effects of individual meteorological and chemical processes on the temporal evolution of the episode are assessed quantitatively in the present work. The performance of the modelling system was briefly evaluated. The modelling system was able to capture the evolution of the episode, with increasing ozone levels during the period 1–4 August 2003, and maximum values afterwards. Analysis of the results of the CMAQ model indicates that three mechanisms were mainly responsible for the episode: (i) horizontal transport from mainland Europe in the presence of a long-lived high-pressure system, (ii) convergence of westerly and easterly near-surface winds, and (iii) downward entrainment of ozone-rich air from residual layers in the free troposphere. The downward entrainment of ozone from residual layers in the morning is found to be key to enhancing ozone levels during the day. The relevance of this mechanism is supported by the good agreement of the model vertical ozone distribution with that derived from Light detection and ranging (Lidar) measurements. The process analysis of the rate of change of ozone concentration shows that both horizontal transport and vertical transport were equally important in explaining the variability of ozone. The contribution of chemical processes to the increase of ozone concentration as simulated by the modelling system is relatively small close to the surface. However, its contribution to the decrease of ozone concentration there becomes as important as that of meteorological processes. By investigating the role of separate meteorological and chemical mechanisms, this study hopes to add to the current understanding of the evolution of air pollution episode.► First application of WRF-CMAQ to investigate 2003 ozone episode over SE England. ► Entrainment of ozone from the residual layer increases the surface ozone concentration. ► Surface convergence of westerly and easterly winds enhances ozone levels. ► Ozone evolution can be influenced critically by scale dependent meteorological processes.
Keywords: Process rate analysis; Ozone; Heatwave; CMAQ
Particulate matter (PM10) in Istanbul: Origin, source areas and potential impact on surrounding regions by M. Koçak; C. Theodosi; P. Zarmpas; U. Im; A. Bougiatioti; O. Yenigun; N. Mihalopoulos (pp. 6891-6900).
Water-soluble ions (Cl−,NO3−,SO42−,C2O4−, Na+,NH4+, K+, Mg2+,Ca2+), water soluble organic carbon (WSOC), organic and elemental carbon (OC, EC) and trace metals (Al, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Cd and Pb) were measured in aerosol PM10 samples above the megacity of Istanbul between November 2007 and June 2009. Source apportionment analysis using Positive Matrix Factorization (PMF) indicates that approximately 80% of the PM10 is anthropogenic in origin (secondary, refuse incineration, fuel oil and solid fuel combustion and traffic). Crustal and sea salt account for 10.2 and 7.5% of the observed mass, respectively. In general, anthropogenic (except secondary) aerosol shows higher concentrations and contributions in winter. Mean concentration and contribution of crustal source is found to be more important during the transitional period due to mineral dust transport from North Africa. During the sampling period, 42 events exceeding the limit value of 50 μg m−3 are identified. A significant percentage (91%; n = 38) of these exceedances is attributed to anthropogenic sources. Potential Source Contribution Function analysis highlights that Istanbul is affected from distant sources from Balkans and Western Europe during winter and from Eastern Europe during summer. On the other hand, Istanbul sources influence western Black Sea and Eastern Europe during winter and Aegean and Levantine Sea during summer.
Keywords: Istanbul; Source apportionment; Potential source contribution function; PM; 10
Meteorological and air quality forecasting using the WRF–STEM model during the 2008 ARCTAS field campaign by Alessio D’Allura; Sarika Kulkarni; Gregory R. Carmichael; Sandro Finardi; Bhupesh Adhikary; Chao Wei; David Streets; Qiang Zhang; Robert B. Pierce; Jassim A. Al-Saadi; Glenn Diskin; Paul Wennberg (pp. 6901-6910).
In this study, the University of Iowa’s Chemical Weather Forecasting System comprising meteorological predictions using the WRF model, and off-line chemical weather predictions using tracer and full chemistry versions of the STEM model, designed to support the flight planning during the ARCTAS 2008 mission is described and evaluated. The system includes tracers representing biomass burning and anthropogenic emissions from different geographical emissions source regions, as well as air mass age indicators. We demonstrate how this forecasting system was used in flight planning and in the interpretation of the experimental data obtained through the case study of the summer mission ARCTAS DC-8 flight executed on July 9 2008 that sampled near the North Pole. The comparison of predicted meteorological variables including temperature, pressure, wind speed and wind direction against the flight observations shows that the WRF model is able to correctly describe the synoptic circulation and cloud coverage in the Arctic region The absolute values of predicted CO match the measured CO closely suggesting that the STEM model is able to capture the variability in observations within the Arctic region. The time–altitude cross sections of source region tagged CO tracers along the flight track helped in identifying biomass burning (from North Asia) and anthropogenic (largely China) as major sources contributing to the observed CO along this flight. The difference between forecast and post analysis biomass burning emissions can lead to significant changes (∼10–50%) in primary CO predictions reflecting the large uncertainty associated with biomass burning estimates and the need to reduce this uncertainty for effective flight planning.► Demonstrates novel uses of chemical weather forecasts in support of the ARCTAS mission. ► WRF meteorology model is shown to successfully describe Arctic synoptic circulation. ► The North Pole region was impacted by anthropogenic and fire emissions from Asia. ► Further improvements in prediction skills requires improved fire emission estimates.
Keywords: ARCTAS; Arctic; Air quality forecasting; Chemical weather
Evaluation of diabatic initialization improvements in the numerical weather prediction model Hirlam, focusing on the effect this may have on precipitation and dispersion forecasts by G.T. Geertsema; B.G.J. Wichers Schreur (pp. 6911-6916).
Amongst the key issues concerning mesoscale modeling capability for air pollution and dispersion applications are precipitation and cloud cover forecasts. The long-standing problem of the spin-up of clouds and precipitation in numerical weather prediction models limits the accuracy of the prediction of short-range dispersion and deposition from local sources. Customary the spin-up problem is avoided by only using NWP forecasts with a lead time greater than the spin-up time of the model. Due to the increase of uncertainty with forecast range this reduces the quality of the associated forecasts of the atmospheric flow.Improvements through diabatic initialization in the spin-up of large-scale precipitation in the Hirlam NWP model are discussed. In a synthetic example the effects of these improvements on a dispersion forecast are explored specifically for wet deposition. Using a case study of several weeks the optimal lead time for precipitation is discussed.The analysis presented in this paper leads to the conclusion that, at least for situations where large-scale precipitation dominates, proper diabatic initialization of a weather model may limit spin-up so that its full forecast range can be used. The implication for dispersion modeling is that such an improved model is particularly useful for short-range forecasts and the calculation of local deposition. The sensitivity of the hydrological process to proper initialization implies that the spin-up problem may reoccur with changes in the model and increased model resolution. This is demonstrated using a recent version of Hirlam. Spin-up should therefore not only be an ongoing concern for atmospheric modelers, but a reason for close cooperation with dispersion modelers.► We have modeled the effect of precipitation spin-up on dispersion forecasts. ► We find that precipitation spin-up may deteriorate dispersion forecasts. ► Diabatic initialization seems essential for the alleviation of spin-up. ► Changes in the weather model may cause new spin-up effects. ► Extension of precipitation verification with dispersion specific methods is vital.
Keywords: Relaxation process; Precipitation; Wet deposition; Emergency response; Air pollution; Mesoscale modeling; Dispersion modeling
A European open access chemical weather forecasting portal by Taru Balk; Jaakko Kukkonen; Kostas Karatzas; Tassos Bassoukos; Victor Epitropou (pp. 6917-6922).
A European chemical weather forecasting portal is presented in this paper that has been developed within the COST (European Cooperation in Science and Technology) ES0602 action, “Towards a European Network on Chemical Weather Forecasting and Information Systems”. The portal includes an access to a substantial number (currently 21) of available chemical weather forecasting systems and their numerical forecasts; these cover in total more than 30 regions in Europe. This portal can be used, e.g., to find out, which services are available for a specific domain, for specific source categories or for specific pollutants. The portal currently expands its functionalities to allow for a harmonized presentation and inter-comparison of the various available forecasts, as well as for the computation of model ensemble predictions. It provides functions for obtaining relevant supplementary information, e.g., using the Model Documentation System of the European Environmental Agency. The new portal is an open access system, through which chemical weather forecasts can be added to the system, and the predictions can be accessed, analysed and inter-compared. Such a single point of reference for the European chemical weather forecasting information has previously not been in operation. We present the characteristics of the new portal, and discuss how this activity complements the GEMS and PROMOTE air quality forecasting portals.
Keywords: Forecast; Portal; Chemical weather; Ensemble; ECWFP; Chemical transport model
Fertilizer-induced emission factors and background emissions of N2O from vegetable fields in China by Jinyang Wang; Zhengqin Xiong; Xiaoyuan Yan (pp. 6923-6929).
The estimation of nitrous oxide (N2O) emissions based on specific cropping systems is important for accurate national N2O budgets. Intensively managed vegetable cultivation is responsible for large N2O emissions in mainland China. However, little information can be obtained on the nationwide estimation of direct N2O emissions from vegetable fields. Estimates of fertilizer-induced direct N2O emissions from vegetable fields in mainland China were thus obtained by compiling and analyzing reported data in peer-reviewed journals and research reports. The results indicated that the seasonal N2O emissions from vegetable fields significantly increased with nitrogen (N) fertilizer application ( p < 0.0001). According to the ordinary least squares (OLS) model, the fertilizer-induced emission factor (EF) and background emissions of N2O were estimated to be 0.55 ± 0.05% and 1.067 ± 0.277 kg N ha−1 yr−1, respectively. The EF was reduced and the background emission of N2O increased when the measurement duration was prolonged from ≤100 d to >100 and ≤200 d. Comparable results were obtained by the maximum likelihood (ML) model, with an EF of 0.49 ± 0.06% and background N2O emissions of 1.228 ± 0.189 kg N ha−1 yr−1. Based on the OLS-derived parameters, the fertilizer-induced direct emissions and background emissions of N2O were estimated to be 66.95 Gg N and 19.63 Gg N, respectively, in 2009, and the annual N2O emissions were much higher in the provinces of Shandong, Henan, Hebei and Sichuan. The estimated N2O emissions from vegetable fields accounted for 21.4% of the total direct N2O emissions from Chinese croplands, with large uncertainties. Therefore, the EF and background emissions of N2O for each cropping system, particularly for intensively managed vegetable fields, should be specifically determined for accurate national N2O inventories.► Estimation of EF and background emission of N2O from Chinese vegetable fields. ► Comparable estimates of EF and background emission obtained by maximum likelihood- and ordinary least squares-models. ► Estimation of provincial distribution of direct N2O emission from vegetable fields.
Keywords: N; 2; O budget; Model estimation; Vegetable cultivation; Cropping system; Climate change
Analysis of ultraviolet radiation in clear skies in Beijing and its affecting factors by Jianhui Bai (pp. 6930-6937).
Analyzing observational data for solar radiation, meteorological parameters and total ozone concentration during the period of January 1990 to December 1991 in Beijing enabled the development of an empirical method for estimation of UV irradiance (UVI) in clear skies. Predicted values from the model agreed well with observations. The mean relative bias for 24 months was 1.9%. UVI (290–400nm) in clear sky conditions from 1979 to 1998 was calculated, and its long-term variation showed a declining trend of −3.89%, which was accompanied by a decrease in total O3 of −5.75%, a decrease in scattering factor ( S/ D, the ratio of solar scattered to direct radiation) of −20.79%, and an increase in water vapor content of +4.76%. It is hypothesized that many substances in the atmosphere, including volatile organic compounds (VOCs) and their oxidation products, very fine particles and others absorb and/or utilize UV energy. The long-term UVI trends and its main controlling factors in four seasons during the previous 2 decades are discussed, UV energy consumption by atmospheric chemical and photochemical processes, is especially important during summer.► An empirical model for studying UV irradiation (UVI) in Beijing was established. ► The predicted UVI in clear skies agreed with observations. ► UVI in Beijing in clear sky from 1979 to 1998 showed a declining trend of −3.89%. ► An unexpected UVI decrease in summer and its mechanism were discussed. ► UV loss by the GLP utilization plays an important role and should be studied.
Keywords: UV radiation; Clear sky; UV energy absorption; Volatile organic compounds
Impact of source collinearity in simulated PM2.5 data on the PMF receptor model solution by Rima Habre; Brent Coull; Petros Koutrakis (pp. 6938-6946).
Positive Matrix Factorization (PMF) is a factor analytic model used to identify particle sources and to estimate their contributions to PM2.5 concentrations observed at receptor sites. Collinearity in source contributions due to meteorological conditions introduces uncertainty in the PMF solution. We simulated datasets of speciated PM2.5 concentrations associated with three ambient particle sources: “Motor Vehicle” (MV), “Sodium Chloride” (NaCl), and “Sulfur” (S), and we varied the correlation structure between their mass contributions to simulate collinearity. We analyzed the datasets in PMF using the ME-2 multilinear engine. The Pearson correlation coefficients between the simulated and PMF-predicted source contributions and profiles are denoted by “ G correlation” and “ F correlation”, respectively. In sensitivity analyses, we examined how the means or variances of the source contributions affected the stability of the PMF solution with collinearity. The % errors in predicting the average source contributions were 23, 80 and 23% for MV, NaCl, and S, respectively. On average, the NaCl contribution was overestimated, while MV and S contributions were underestimated. The ability of PMF to predict the contributions and profiles of the three sources deteriorated significantly as collinearity in their contributions increased. When the mean of NaCl or variance of NaCl and MV source contributions was increased, the deterioration in G correlation with increasing collinearity became less significant, and the ability of PMF to predict the NaCl and MV loading profiles improved. When the three factor profiles were simulated to share more elements, the decrease in G and F correlations became non-significant. Our findings agree with previous simulation studies reporting that correlated sources are predicted with higher error and bias. Consequently, the power to detect significant concentration-response estimates in health effect analyses weakens.► We simulate collinearity in the mass contributions of three ambient particle sources. ► We analyze the speciated PM2.5 data in PMF and compare model inputs to outputs. ► The PMF solution deteriorates significantly as source collinearity increases. ► Sources with higher coefficients of variation are predicted with lower error. ► Sources with higher mean contributions are predicted with lower error.
Keywords: PMF; Receptor model; Source collinearity; Simulation; PM; 2.5; Source apportionment
Seasonality in size segregated biogenic, anthropogenic and sea salt sulfate aerosols over the North Atlantic by Alison Michelle Seguin; Ann-Lise Norman; Sarah Eaton; Moire Wadleigh (pp. 6947-6954).
Size segregated aerosol sulfate concentration was measured over a south to north transect of the North Atlantic, extending from 37° N to the base of Greenland, during spring, summer and fall of 2003. Sea salt sulfate for all three seasons was found in large diameter aerosols (>0.95 μm), but spring season sea salt was also persistently found in the finest aerosols collected (<0.49 μm). Non sea salt sulfate concentrations in the 0.49–0.95 μm range (large accumulation mode) were elevated in summer (5.7 ± 7.0 nmol m−3) relative to spring (1.4 ± 0.7 nmol m−3) and fall (1.3 ± 1.0 nmol m−3). Non sea salt sulfate was apportioned into biogenic and anthropogenic sulfate using sulfur isotopes. Little to no biogenic sulfate was observed in the spring. However, in the summer and fall biogenic sulfate concentration averaged 2.3 ± 1.4 nmol m−3 and 2.0 ± 2.2 nmol m−3 respectively in aerosols less than 0.49 μm diameter corresponding to approximately 40% of the non sea salt sulfate load for both seasons. Anthropogenic sulfate was detectable throughout the study with the largest concentrations of fine aerosol anthropogenic sulfate (up to 76 nmol m−3) observed in samples collected at lower latitudes.Stable isotopes were used to determine aerosol growth from local SO2 oxidation in the summer. SO2 oxidation is calculated to be significant in two aerosol growth events. These samples had the largest biogenic sulfate concentrations in the 0.49–0.95 μm range aerosols and showed high concentrations of sulfate in the 0.49–0.95 μm relative to the <0.49 μm diameter aerosols. Sulfate from local SO2 oxidation was calculated to be approximately 40% of the non sea salt sulfate present in these two events.► North Atlantic size segregated aerosol SO4 concentrations measured over 3 seasons. ► Anthropogenic and biogenic sulfate concentrations determined by isotope apportionment. ► Sea Salt found in <0.49 μm spring aerosols not present in other seasons. ► Elevated summer NSS SO4 in 0.49 μm–0.95 μm aerosols relative to other seasons. ► Evidence of aerosol growth events from SO2 oxidation in summer.
Keywords: Sulfur isotope; Marine aerosol; Sea salt Sulfate; Anthropogenic influence; Aerosol growth mechanism
Characteristics of fine particle carbonaceous aerosol at two remote sites in Central Asia by Justin P. Miller-Schulze; Martin M. Shafer; James J. Schauer; Paul A. Solomon; Jeffrey Lantz; Maria Artamonova; Boris Chen; Sanjar Imashev; Leonid Sverdlik; Greg R. Carmichael; Jeff T. Deminter (pp. 6955-6964).
Central Asia is a relatively understudied region of the world in terms of characterizing ambient particulate matter (PM) and quantifying source impacts of PM at receptor locations, although it is speculated to have an important role as a source region for long-range transport of PM to Eastern Asia, the Pacific Ocean, and the Western United States. PM is of significant interest not only because of its adverse effect on public health but also due to its more recently realized role in climate change. To investigate the sources and characteristics of PM in the region, a series of PM2.5 and PM10 samples were collected on an every-other-day basis at two sites (termed “Bishkek” and “Teploklyuchenka”) in the Central Asian nation of the Kyrgyz Republic (also known as Kyrgyzstan) for a full year from July 2008 to July 2009. These samples were analyzed using standard methods for mass, organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), water-insoluble organic carbon by difference (OC minus WSOC) and a variety of molecular marker chemical species to be used in a chemical mass balance (CMB) model to apportion the sources of OC. These analyses indicate that approximately 19 ± 6.4% of the PM2.5 mass at both sites throughout the year consists of OC. The carbonaceous component of PM2.5 is dominated by OC, with OC/Total Carbon (TC) ratios being around 0.8 in the winter to almost 0.95 in the summer months. The CMB analysis indicated that mobile sources, i.e., gasoline and diesel engine exhaust, biomass combustion, and biogenic secondary organic aerosol (SOA) formation from isoprene and α-pinene precursors in the summer months were the dominant sources of OC. A strong positive correlation was observed between non-biomass burning WSOC and the un-apportioned OC from the CMB analysis, indicating that some of this un-apportioned OC is WSOC and likely the result of SOA-forming atmospheric processes that were not estimated by the CMB analysis performed. In addition, a comparison of the predominant contributors to OC between the two sites indicates that biomass combustion is a stronger relative source of OC at the Teploklyuchenka site, particularly in the winter, while contributions of isoprene- and α-pinene-derived SOA to the measured OC was relatively similar between the sites.► Organic Carbon (OC) is a significant constituent of PM2.5 aerosol at 2 sites in the Kyrgyz Republic. ► The main sources of OC at both sites as determined by CMB were mobile sources and biomass combustion. ► Secondary Organic Aerosol was estimated to be a significant source of OC in the summer months.
Keywords: Chemical mass balance; Source apportionment; Carbonaceous aerosol
Ozone deposition velocities, reaction probabilities and product yields for green building materials by S.P. Lamble; R.L. Corsi; G.C. Morrison (pp. 6965-6972).
Indoor surfaces can passively remove ozone that enters buildings, reducing occupant exposure without an energy penalty. However, reactions between ozone and building surfaces can generate and release aerosols and irritating and carcinogenic gases. To identify desirable indoor surfaces the deposition velocity, reaction probability and carbonyl product yields of building materials considered green (listed, recycled, sustainable, etc.) were quantified. Nineteen separate floor, wall or ceiling materials were tested in a 10 L, flow-through laboratory reaction chamber. Inlet ozone concentrations were maintained between 150 and 200 ppb (generally much lower in chamber air), relative humidity at 50%, temperature at 25 °C and exposure occurred over 24 h. Deposition velocities ranged from 0.25 m h−1 for a linoleum style flooring up to 8.2 m h−1 for a clay based paint; reaction probabilities ranged from 8.8 × 10−7 to 6.9 × 10−5 respectively. For all materials, product yields of C1 thru C12 saturated n-aldehydes, plus acetone ranged from undetectable to greater than 0.70 The most promising material was a clay wall plaster which exhibited a high deposition velocity (5.0 m h−1) and a low product yield (
Keywords: Ozone; Building materials; Passive control; Surface chemistry; Carbonyl products; Green buildings
Kinetic study of gas phase reactions of OH with CF3CH2OH, CF3CF2CF2CH2OH, and CHF2CF2CH2OH using LP-LIF method by Y.N. Indulkar; S. SenGupta; S.B. Waghmode; A. Kumar; S. Dhanya; P.D. Naik (pp. 6973-6979).
The rate coefficients for the reactions of OH radicals with three fluoroalcohols, CF3CH2OH ( k1), CF3CF2CF2CH2OH ( k2), and CHF2CF2CH2OH ( k3), have been measured in the temperature range of 298–363K, at a total pressure of ∼55torr, using LP-LIF method. The kinetic parameters measured for CF3CH2OH, which is well studied, matches with the previous reports within error limits. The rate expression for k2 is (1.54±0.80)×10−12 exp (−765±170)/ T), and for k3 is (1.12±0.26)×10−12 exp (−560±80)/ T). Based on the above values of the rate coefficients, the tropospheric lifetimes with respect to removal by reaction with OH have been estimated to be 0.38 and 0.26 years for CF3CF2CF2CH2OH and CHF2CF2CH2OH respectively, supporting their potential use as HFC alternatives. The results are discussed along with the literature data on other fluoroalcohols. The present study is aimed to assess the effect of additional CF2 groups and H atoms on tropospheric lifetime and global warming potential of fluoroalcohols. The results confirm that the rate coefficients at room temperature and activation energy parameters are independent of n, for the reaction of OH with fluoroalcohols of general formula CF3(CF2) nCH2OH, which are potential CFC/HFC alternatives.► Kinetics of reactions of OH with 3 fluoroalcohols, potential CFC/HFC alternatives. ► k and Ea similar for CF3CH2OH and CF3(CF2)2CH2OH, independent of number of CF2 groups. ► Higher k and lower Ea with H substitution at terminal C atom in CHF2CF2CH2OH. ► Tropospheric lifetimes – C2F5CH2OH – 0.38, CHF2CF2CH2OH – 0.26 years.
Keywords: Fluoroalcohols; OH radical; Rate constants; Tropospheric lifetime
Adjoint model enhanced plume reconstruction from tomographic remote sensing measurements by Eduardo P. Olaguer (pp. 6980-6986).
A new mathematical optimization method is presented for reconstructing pollution plume concentrations from tomographic remote sensing measurements on neighborhood scales (about 1 km × 1 km) using Differential Optical Absorption Spectroscopy (DOAS). The new method, called CAT–4Dvar, combines Computer Aided Tomography (CAT) and 4D variational (4Dvar) data assimilation. The objective of the method is to produce accurate reconstructions compared to the Algebraic Reconstruction Technique (ART) and other non-variational methods with only a small number of DOAS telescopes. A forward and adjoint 3D grid dispersion model was developed based on advection and diffusion solvers commonly used in air quality modeling. The adjoint model optimizes the model emissions and horizontal diffusion coefficient based on the difference between tomographic DOAS observations and ray path-integrated concentrations predicted by the forward model. It also updates the corresponding error covariances based on the Hessian of the cost function. An enhanced reconstruction is obtained from the forward model with optimized parameter values. In a synthetic experiment involving two hypothetical DOAS instruments, the CAT–4Dvar method yielded excellent results compared to ART, reducing the overall nearness index from 57% to 11%.► A new method is presented for reconstructing plumes via tomographic remote sensing. ► The method uses a forward and adjoint dispersion model to optimize model parameters. ► The method produces accurate reconstructions with only two remote sensing telescopes. ► The new method compares favorably with the Algebraic Reconstruction Technique.
Keywords: Tomography; Remote sensing; Adjoint dispersion model; 4D variational method; Data assimilation; Plume reconstruction
Experimental investigation of submicron and ultrafine soot particle removal by tree leaves by Hee-Jae Hwang; Se-Jin Yook; Kang-Ho Ahn (pp. 6987-6994).
Soot particles emitted from vehicles are one of the major sources of air pollution in urban areas. In this study, five kinds of trees were selected as Pinus densiflora, Taxus cuspidata, Platanus occidentalis, Zelkova serrata, and Ginkgo biloba, and the removal of submicron (<1 μm) and ultrafine (<0.1 μm) soot particles by tree leaves was quantitatively compared in terms of deposition velocity. Soot particles were produced by a diffusion flame burner using acetylene as the fuel. The sizes of monodisperse soot particles classified with the Differential Mobility Analyzers (DMA) were 30, 55, 90, 150, 250, 400, and 600 nm. A deposition chamber was designed to simulate the omni-directional flow condition around the tree leaves. Deposition velocities onto the needle-leaf trees were higher than those onto the broadleaf trees. P. densiflora showed the greatest deposition velocity, followed by T. cuspidata, Platanus occidentalis, Zelkova serrata, and Ginkgo biloba. In addition, from the comparison of deposition velocity between two groups of Platanus occidentalis leaves, i.e. one group of leaves with front sides only and the other with back sides only, it was supposed in case of the broadleaf trees that the removal of airborne soot particles of submicron and ultrafine sizes could be affected by the surface roughness of tree leaves, i.e. the veins and other structures on the leaves.► Submicron and ultrafine soot particle removal by tree leaves was investigated. ► Deposition velocity was used for the quantitative comparison of particle removal. ► Pinus densiflora showed the greatest deposition velocity, followed by. ► Taxus cuspidata, Platanus occidentalis, Zelkova serrata, and Ginkgo biloba. ► Airborne soot particle removal can be affected by surface roughness of tree leaves.
Keywords: Deposition velocity; Ultrafine soot; Air pollution; Tree; Leaf
Estimation of county-level black carbon emissions and its spatial distribution in China in 2000 by Y. Qin; S.D. Xie (pp. 6995-7004).
A more accurate emission inventory of Black Carbon (BC) from China in 2000 was established based on county-level statistical data and recently published emission factors (EFs) from local measurements, which were further gridded at 0.5° × 0.5°. A comprehensive database for BC emission factors was compiled for main anthropogenic sources. BC emissions from China in 2000 were estimated to be 1228.52 Gg under normal operating conditions, and would increase to 2136.53 Gg if failures in control devices and combustion were considered. Spatial distribution of national BC emissions and emissions from different sources were determined; districts with extraordinarily high emissions cover 18.0% of China’s territory but generated 69.14% of the total emissions. Separate EFs were developed for each vehicle type fueled with gasoline or diesel; both the absolute value and relative share of BC emissions from vehicles in this work were higher than those in previous reports, suggesting that previous studies which did not differentiate vehicle types may have underestimated vehicle emissions.► A database for black carbon emission factors is compiled. ► Absolute value and relative share of vehicular BC emissions are higher in this work. ► Monte Carlo simulation estimates the inventory uncertainty as [−49.45%, 136.71%].
Keywords: Black carbon; Emission inventory; Spatial distribution; China
PM10 forecasting using clusterwise regression by Jean-Michel Poggi; Bruno Portier (pp. 7005-7014).
In this paper, we are interested in the statistical forecasting of the daily mean PM10 concentration. Hourly concentrations of PM10 have been measured in the city of Rouen, in Haute-Normandie, France. Located at northwest of Paris, near the south side of Manche sea and heavily industrialised. We consider three monitoring stations reflecting the diversity of situations: an urban background station, a traffic station and an industrial station near the cereal harbour of Rouen. We have focused our attention on data for the months that register higher values, from December to March, on years 2004–2009. The models are obtained from the winter days of the four seasons 2004/2005 to 2007/2008 (training data) and then the forecasting performance is evaluated on the winter days of the season 2008/2009 (test data).We show that it is possible to accurately forecast the daily mean concentration by fitting a function of meteorological predictors and the average concentration measured on the previous day. The values of observed meteorological variables are used for fitting the models and are also considered for the test data. We have compared the forecasts produced by three different methods: persistence, generalized additive nonlinear models and clusterwise linear regression models. This last method gives very impressive results and the end of the paper tries to analyze the reasons of such a good behavior.► We consider the statistical forecasting of the daily mean PM10 concentration. ► Three monitoring stations in the city of Rouen, France, are considered. ► Models use previous PM10 values and meteorological variables. ► Clusterwise linear models provide accurate forecasts and outperform two competitors. ► Such a model is detailed in one station, highlighting the reasons of such results.
Keywords: Particulate matter; Forecasting; Clusterwise linear models; Generalized additive models; Random forests; Rouen