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Atmospheric Environment (v.43, #11)

Editorial board (pp. i).

The variability of free tropospheric ozone over Beltsville, Maryland (39N, 77W) in the summers 2004–2007 by John E. Yorks; Anne M. Thompson; Everette Joseph; Sonya K. Miller (pp. 1827-1838).
Ozone profiles are often used to investigate day-to-day and year-to-year variability in origins of free tropospheric ozone. With this in mind, more than 50 ozonesonde launches were conducted in Beltsville, MD, during the summers of 2004 through 2007. Budgets of free tropospheric ozone were calculated for each ozone profile in the four summers using a laminar identification (LID) method and unusual episodes were analyzed with respect to meteorological variables. The laminar method showed that stratosphere-to-troposphere transport (ST) accounted for greater than 50% of the free tropospheric ozone column on 17% of days sampled, a more pronounced influence than regional convective and lightning (RCL) sources. The ST origins were confirmed with trajectories, and tracers (water vapor and potential vorticity). The amount of free tropospheric ozone from ST and RCL sources varied from year-to-year (up to 13%) and can be explained by differences in mean meteorological patterns. On average, almost 30% of the free tropospheric column was attributed to ST influence, about twice as much as RCL, although the LID method may not capture weeks-old lightning influences as in a chemical model. The prevalence of ST ozone in summertime Beltsville soundings was similar to six sounding sites in the IONS-04 campaign [Thompson, A.M., et al., 2007b. Intercontinental Transport Experiment Ozonesonde Network Study (IONS, 2004): 1. Summertime upper tropospheric/lower stratosphere ozone over northeastern North America. J. Geophys. Res. 112, D12S12; Thompson, A.M., et al., 2007c. Intercontinental Transport Experiment Ozonesonde Network Study (IONS, 2004): 2. Tropospheric ozone budgets and variability over northeastern North America. J. Geophys. Res. 112, D12S13.] and to statistics from a 30year climatology of European soundings [Collette, A., Ancellet, G., 2005. Impact of vertical transport processes on the tropospheric ozone layering above Europe. Part II: Climatological analysis of the past 30years. Atmos. Environ. 39, 5423–5435]. The Beltsville record also demonstrated the value of soundings for air quality forecasting in an urban area. The 22 nighttime soundings collected over Beltsville in 2004–2007 can be divided into distinct polluted and unpolluted subsets, the former 20ppbv higher in residual layer ozone (1km) than the latter. These distinctions propagated to daytime differences of 10ppbv at the surface in the Washington, DC, area, with the high-ozone residual layers leading to non-attainment of the National Ambient Air Quality Standard for ozone. More frequent ozone observations aloft appear essential for better understanding ozone variability and for enabling air quality modelers to achieve more accurate ozone forecasts.

Keywords: Ozone; Ozonesonde; Vertical profile; Air quality model; Boundary layer pollution


Evaluation of model simulated atmospheric constituents with observations in the factor projected space: CMAQ simulations of SEARCH measurements by Amit Marmur; Wei Liu; Yuhang Wang; Armistead G. Russell; Eric S. Edgerton (pp. 1839-1849).
Two-year CMAQ simulations of gases and aerosols over the southeast are evaluated using SEARCH observations for 2000 and 2001, both by direct comparison to observations and by projecting both datasets to the factor space using the Positive Matrix Factorization (PMF) model. Model performance for secondary species (sulfate, ozone) is generally better than for primary species (EC, CO). Nitrate concentrations are overestimated, mainly due to wintertime over-partitioning to the particulate phase. Projecting both observed and simulated constituents to the factor space using PMF, four common factors are resolved for each surface site (two urban sites and two rural sites). The resolved factors include (1) secondary sulfate, (2) secondary nitrate, (3) a fresh motor vehicle factor characterized by EC, OC, CO, NO and NO y, and (4) a mixed factor characterized by EC, OC, and CO. Performance for the sulfate and nitrate factors follow that of the corresponding driving species, while the motor vehicle and “mixed” factors exhibit performance corresponding to that of primary species. Comparing observations and CMAQ simulations in the projected space allow for an evaluation of the co-variability between species, an indicator of source impacts. The fact that similar factors were resolved by PMF from both the observations and the CMAQ simulations suggests that temporal processes related to emissions from specific source categories, as well as the subsequent dispersion and reactivity, are well captured by the CMAQ model. The ability to identify additional factors can be enhanced by adding tracer species in CMAQ simulations.

Keywords: PMF; CMAQ; Source apportionment; PM; 2.5; SEARCH


Individual particle characteristics of North African dust under different long-range transport scenarios by Esther Coz; Francisco J. Gómez-Moreno; Manuel Pujadas; Gary S. Casuccio; Traci L. Lersch; Begoña Artíñano (pp. 1850-1863).
After urban sources, mineral dust in Madrid is the second biggest contributor to PM10, making up 40% on average, of total emissions. Approximately, 50% of the days on which the daily limit of 50 μgm−3 marked by the European Directive, are ascribable to Saharan outbreaks. The present study has focused on individual particle characterization of North African dust over Madrid by SEM/EDX, since no previous works on this type of characterization have been found in the region. More than 30,000 particles from 6 different samples have been measured to characterize 4 African episodes with very different meteorological scenarios, transport processes and source origins. Different samples from the same episode have also been characterized to evaluate homogeneity of dust characteristics over time. Silicates, mainly composed of clay minerals, are the main component, with abundances ranging from 65 to 85% by particle volume. Chemical cluster distribution of silicates has been linked to the major topsoil mineralogical composition in the origin of the episodes. Aspect Ratio (AR) has been used to compare particle morphology between episodes. AR values from samples taken under the same scenarios are statistically equal. For all the samples and size ranges AR values are found to be in the same order: ARsulphates>ARsilicates>ARcarbonates. Particles not only maintained morphology during the episode, but also chemical composition, since clusters turned out to be very similar in samples taken on the same day and different days. Similarities and differences in particle chemical composition and morphology between the different transport patterns are discussed in detail throughout the paper.

Keywords: African dust; Particle morphology; CCSEM/EDX; Dust origin


Evaluation of a unified regional air-quality modeling system (AURAMS) using PrAIRie2005 field study data: The effects of emissions data accuracy on particle sulphate predictions by S. Cho; P.A. Makar; W.S. Lee; T. Herage; J. Liggio; S.M. Li; B. Wiens; L. Graham (pp. 1864-1877).
The effects of the accuracy of major-point source emissions input data on the predictions of a regional air-quality model (AURAMS) were investigated through a series of scenario simulations. The model domain and time period were chosen to correspond to that of PrAIRie2005, an air-quality field study with airborne and ground-based mobile measurement platforms that took place between August 12th and September 7th, 2005, over the city of Edmonton, Alberta, Canada. The emissions data from standard sources for three coal-fired power-plants located west (typically upwind) of the city were compared to the continuous emissions monitoring system (CEMS) taking place at the time of the study – the latter showed that the original emissions inventory data considerably overestimated NO x, SO2, and primary particulate emissions during the study period. Further field investigation (stack sampling) in the fall of 2006 showed that the measured primary particle size distribution and chemical speciation for the emissions were strikingly different from the distribution and speciation originally used in the model. The measured emissions were used to scale existing emissions data in accord with the CEMS and in-stack measurements.The effects of these improvements to the emissions data were examined sequentially in nested AURAMS simulations (finest horizontal resolution 3km), and were compared to airborne aerosol mass spectrometer (Aerodyne AMS) measurements of particle sulphate, and particle distributions from an airborne passive cavity aerosol spectrometer probe (PCASP). The emissions of SO2 had the greatest impact on predicted PM1 sulphate, while the primary particle size distribution and chemical speciation had a smaller role. The revised emissions data greatly improved the comparisons between observations and model values, though over-predictions of fine-mode sulphate still occur near the power-plants, with the use of the revised emissions data. The modified emissions also had a significant impact on the larger particles of the particulate matter, with more primary PM in sizes greater than 1μm diameter than had previously been estimated, and higher large particle concentrations close to the power-plants.

Keywords: Urban emission modelling; Emission uncertainty; Model improvement; Air quality model evaluation; Sulphate particle


Adjoint inverse modeling of NO x emissions over eastern China using satellite observations of NO2 vertical column densities by Jun-ichi Kurokawa; Keiya Yumimoto; Itushi Uno; Toshimasa Ohara (pp. 1878-1887).
A four-dimensional variational data assimilation system for optimization of NO x emissions (RC4-NO x) was developed. A parameterized NO x chemistry scheme was introduced into the RC4-NO x system, and key parameters such as chemical production and loss terms of NO x were calculated in advance using the Community Multiscale Air Quality (CMAQ) modeling system. RC4-NO x was applied to optimize NO x emissions over eastern China (EC) in July 1996, 1999, and 2002 using Global Ozone Monitoring Experiment (GOME) satellite observations of NO2 vertical column densities (VCDs) and a priori emissions from the Regional Emission Inventory in Asia (REAS). After assimilation, RC4-NO x generally reproduced the spatial distribution, regional averaged values, and time evolution of GOME NO2 VCDs. Over EC, a priori emissions were reduced by 20% in 1996 and by 8% in 1999, whereas a posteriori emissions were almost the same as a priori emissions in 2002. A priori emissions in the Beijing region were reduced by optimization over the whole simulation period. A posteriori emissions over the Yangtze Delta were larger than a priori emissions in 2002, although they were smaller in both 1996 and 1999. As in other areas, a priori emissions over the North China Plain were reduced in 1996; but those over the eastern part of the plain were increased in 1999, and the area of increased emissions moved slightly westward in 2002. In each region, the growth rates of a posteriori emissions during both 1996–1999 and 1999–2002 became generally larger than those of a priori emissions, and the trends of a posteriori emissions became similar to those of GOME NO2 VCDs. Our inverse modeling analysis indicates that the rate of increase of NO x emissions over EC from 1996 to 2002 was much larger for a posteriori emissions (49%) than for a priori emissions (19%).

Keywords: Inverse modeling; Adjoint model; Emission inventory; Nitrogen oxides; China


Comparison of manual and automated chambers for field measurements of N2O, CH4, CO2 fluxes from cultivated land by Zhisheng Yao; Xunhua Zheng; Baohua Xie; Chunyan Liu; Baoling Mei; Haibo Dong; Klaus Butterbach-Bahl; Jianguo Zhu (pp. 1888-1896).
Chamber techniques can easily be applied to field trials with multiple small plots measuring carbon- and nitrogen-trace gas fluxes. Nevertheless, such chamber measurements are usually made weekly and rarely more frequently than once daily. However, automatic chambers do allow flux measurements on sub-daily time scales. It has been hypothesized that sub-daily measurements provide more reliable results, as diurnal variations are captured better compared to manual measurements. To test this hypothesis we compared automatic and manual measurements of N2O, CO2 and CH4 fluxes from tilled and non-tilled plots of a rice–wheat rotation ecosystem over a non-waterlogged period. Our results suggest that both techniques, i.e., either manual or automatic chambers of N2O and CO2 emissions resulted in biased fluxes. The manual measurements were adequate to capture either day-to-day or seasonal dynamics of N2O, CO2 and CH4 exchanges, but overestimated the cumulative N2O and CO2 emissions by 18% and 31%, respectively. This was due to neglecting temperature-dependent diurnal variations of C and N trace gas fluxes. However, the automatic measurements underestimated the cumulative emissions of N2O and CO2 by 22% and 17%, respectively. This underestimation resulted from chamber effects upon soil moisture during rainfall processes. No significant difference was detected between the two methods in CH4 exchanges over the non-waterlogged soils. The bias of manual chambers may be significant when pronounced diurnal variations occur. The bias of automatic measurements can only be avoided/minimized if chamber positions are frequently changed and/or if chambers are automatically opened during rainfall events. We therefore recommend using automatic chambers together with continuous measurements of soil chamber moisture to allow for soil moisture correction of fluxes or to correct flux estimates as derived by manual chambers for possible diurnal variations.

Keywords: Automated and manual methods; Carbon dioxide; Nitrous oxide; Methane; Rice–wheat rotation


The sensitivity of the CHIMERE model to emissions reduction scenarios on air quality in Northern Italy by A. de Meij; P. Thunis; B. Bessagnet; C. Cuvelier (pp. 1897-1907).
The sensitivity of the CHIMERE model to emission reduction scenarios on particulate matter PM2.5 and ozone (O3) in Northern Italy is studied. The emissions of NO x, PM2.5 SO2, VOC or NH3 were reduced by 50% for different source sectors for the Lombardy region, together with 5 additional scenarios to estimate the effect of local measures on improving the air quality for the Po valley area. Firstly, we evaluate the model performance by comparing calculated surface aerosol concentrations for the standard case (no emission reductions) with observations for January and June 2005. Calculated monthly mean PM10 concentrations are in general underestimated. For June, modelled PM10 concentrations slightly overestimate the measurements. Calculated monthly mean SO4, NO3−, NH4+ concentrations are in good agreement with the observations for January and June. Secondly, the model sensitivity of emission reduction scenarios on PM2.5 and O3 calculated concentrations for the Po valley area is evaluated. The most effective scenarios to abate PM2.5 concentration are based on the SNAP2 (non-industrial combustion plants) and SNAP7 (road traffic) sectors, for which the NO x and PM2.5 emissions are reduced by 50%. The number of days that the 2015 PM2.5 limit value of 25μgm−3 in Milan is exceeded by reducing primary PM2.5 and NO x emissions for SNAP2 and 7 by 50%, does not change in January when compared to the standard case for the Milan area. It appears that 40% of the PM2.5 concentration in the greater Milan area is caused by the emissions surrounding the Lombardy region and from the model boundary conditions.This study also showed that a more effective pollutant reduction (emissions) per ton of pollutant reduced (concentrations) for the greater Milan area is obtained by reducing the primary PM2.5 emissions for SNAP7 by 50%. The most effective scenario on PM2.5 decrease for which precursor emissions are reduced is achieved by reducing SO2 emissions by 50% for SNAP7.Our study showed that during summer time, the largest reductions in O3 concentrations are achieved for SNAP7 emission reductions, when volatile organic compounds (VOCs) are reduced by 50%.

Keywords: Emission scenarios; Particulate matter; Ozone


On-road and laboratory investigation of low-level PM emissions of a modern diesel particulate filter equipped diesel passenger car by Maik Bergmann; Ulf Kirchner; Rainer Vogt; Thorsten Benter (pp. 1908-1916).
Modern diesel particulate filter (DPF) systems are very effective in reducing particle emissions from diesel vehicles. In this work low-level particulate matter (PM) emissions from a DPF equipped EURO-4 diesel vehicle were studied in the emission test laboratory as well as during real-world chasing on a high-speed test track. Size and time resolved data obtained from an engine exhaust particle sizer (EEPS) and a condensation particle counter (CPC) are presented for both loaded and unloaded DPF condition. The corresponding time and size resolved emission factors were calculated for acceleration, deceleration, steady state driving and during DPF regeneration, and are compared with each other. In addition, the DPF efficiency of the tested vehicle was evaluated during the New European Driving Cycle (NEDC) by real time pre-/post-DPF measurements and was found to be 99.5% with respect to PM number concentration and 99.3% for PM mass, respectively. PM concentrations, which were measured at a distance of about 10 m behind the test car, ranged from 1 to 1.5 times background level when the vehicle was driven on the test track under normal acceleration conditions or at constant speeds below 100 kmh−1. Only during higher speeds and full load accelerations concentrations above 3 times background level could be observed. The corresponding tests in the emission laboratory confirmed these results. During DPF regeneration the total PM number emission of nucleation mode particles was 3–4 orders of magnitude higher compared to those emitted at the same speed without regeneration, while the level of the accumulation mode particles remained about the same. The majority of the particles emitted during DPF regeneration was found to be volatile, and is suggested to originate from accumulated sulfur compounds.

Keywords: Diesel exhaust; Nucleation particles; Real-world emission; Diesel particle filter, regeneration


Chemical speciation of PM emissions from heavy-duty diesel vehicles equipped with diesel particulate filter (DPF) and selective catalytic reduction (SCR) retrofits by Subhasis Biswas; Vishal Verma; James J. Schauer; Constantinos Sioutas (pp. 1917-1925).
Four heavy-duty diesel vehicles (HDDVs) in six retrofitted configurations (CRT®, V-SCRT®, Z-SCRT®, Horizon, DPX and CCRT®) and a baseline vehicle operating without after--treatment were tested under cruise (50mph), transient UDDS and idle driving modes. As a continuation of the work by Biswas et al. [Biswas, S., Hu, S., Verma, V., Herner, J., Robertson, W.J., Ayala, A., Sioutas, C., 2008. Physical properties of particulate matter (PM) from late model heavy-duty diesel vehicles operating with advanced emission control technologies. Atmospheric Environment 42, 5622–5634.] on particle physical parameters, this paper focuses on PM chemical characteristics (Total carbon [TC], Elemental carbon [EC], Organic Carbon [OC], ions and water-soluble organic carbon [WSOC]) for cruise and UDDS cycles only. Size-resolved PM collected by MOUDI–Nano-MOUDI was analyzed for TC, EC and OC and ions (such as sulfate, nitrate, ammonium, potassium, sodium and phosphate), while Teflon coated glass fiber filters from a high volume sampler were extracted to determine WSOC. The introduction of retrofits reduced PM mass emissions over 90% in cruise and 95% in UDDS. Similarly, significant reductions in the emission of major chemical constituents (TC, OC and EC) were achieved. Sulfate dominated PM composition in vehicle configurations (V-SCRT®-UDDS, Z-SCRT®-Cruise, CRT® and DPX) with considerable nucleation mode and TC was predominant for configurations with less (Z-SCRT®-UDDS) or insignificant (CCRT®, Horizon) nucleation. The transient operation increases EC emissions, consistent with its higher accumulation PM mode content. In general, solubility of organic carbon is higher (average ∼5 times) for retrofitted vehicles than the baseline vehicle. The retrofitted vehicles with catalyzed filters (DPX, CCRT®) had decreased OC solubility (WSOC/OC: 8–25%) unlike those with uncatalyzed filters (SCRT®s, Horizon; WSOC/OC∼60–100%). Ammonium was present predominantly in the nucleation mode, indicating that ternary nucleation may be the responsible mechanism for formation of these particles.

Keywords: Diesel exhaust particles; Cruise; UDDS; Emission factors; Size fractionated chemical species; Water-soluble organic carbon


Study of the dispersion of VOCs emitted by a municipal solid waste landfill by Rodica Chiriac; Jean Carré; Yves Perrodin; Hervé Vaillant; Santiago Gasso; Philippe Miele (pp. 1926-1931).
The dispersion of VOCs emitted by a municipal solid waste landfill was studied for a period of over one year. Sixteen VOCs were monitored: linear alkanes from C7 to C11, BTEX, trimethylbenzene, trichlorethylene, tetrachlorethylene, α and β-pinenes, limonene. The analytical procedure was first comprised of static long-term sampling of about 2 months using radial diffusion Radiello tubes containing activated carbon, followed by extraction by solvent ( i.e. CS2) and GC/MS analysis. The results were initially analysed on the basis of the total concentration of the quantified VOCs, then by examining the concentrations of certain selected compounds. The influence of different parameters such as operating conditions, meteorological conditions and site morphology was highlighted on the basis of total VOC concentrations. In order to study the VOC's dispersion more closely, 5 compounds were chosen: toluene, benzene, limonene, and the sum trichlorethylene+tetrachlorethylene, as a “marker”, to verify the origin of the VOCs emitted. The results showed that the main source of VOCs is the open cell and lead to different hypotheses on interferences from neighbouring sources and to the proposal of solutions to limit the emission of VOCs and their dispersion. To our knowledge, this type of study has not been accomplished until this day.

Keywords: VOC; Dispersion; Open cell; Landfill; Municipal solid waste


Aerosol physical, chemical and optical properties during the Rocky Mountain Airborne Nitrogen and Sulfur study by E.J.T. Levin; S.M. Kreidenweis; G.R. McMeeking; C.M. Carrico; J.L. Collett Jr.; W.C. Malm (pp. 1932-1939).
During the Rocky Mountain Airborne Nitrogen and Sulfur (RoMANS) study, conducted during the spring and summer of 2006, a suite of instruments located near the eastern boundary of Rocky Mountain National Park (RMNP) measured aerosol physical, chemical and optical properties. Three instruments, a differential mobility particle sizer (DMPS), an optical particle counter (OPC), and an aerodynamic particle sizer (APS), measured aerosol size distributions. Aerosols were sampled by an Interagency Monitoring of Protected Visual Environments (IMPROVE) sampler and a URG denuder/filter-pack system for compositional analysis. An Optec integrating nephelometer measured aerosol light scattering. The spring time period had lower aerosol concentrations, with an average volume concentration of 2.2±2.6μm3cm−3 compared to 6.5±3.9μm3cm−3 in the summer. During the spring, soil was the single largest constituent of PM2.5 mass, accounting for 32%. During the summer, organic carbon accounted for 60% of the PM2.5 mass. Sulfates and nitrates had higher fractional contributions in the spring than the summer. Variability in aerosol number and volume concentrations and in composition was greater in the spring than in the summer, reflecting differing meteorological conditions. Aerosol scattering coefficients (b sp) measured by the nephelometer compared well with those calculated from Mie theory using size distributions, composition data and modeled RH dependent water contents.

Keywords: Visibility; Remote aerosol concentrations; Remote aerosol composition; Rocky Mountain National Park air quality


Rainfall trends in twentieth century over Kerala, India by K.N. Krishnakumar; G.S.L.H.V. Prasada Rao; C.S. Gopakumar (pp. 1940-1944).
Attempts were made to study temporal variation in monthly, seasonal and annual rainfall over Kerala, India, during the period from 1871 to 2005. Longterm changes in rainfall determined by Man-Kendall rank statistics and linear trend. The analysis revealed significant decrease in southwest monsoon rainfall while increase in post-monsoon season over the State of Kerala which is popularly known as the “Gateway of summer monsoon”. Rainfall during winter and summer seasons showed insignificant increasing trend. Rainfall during June and July showed significant decreasing trend while increasing trend in January, February and April. Hydel power generation and water availability during summer months are the concern in the State due to rainfall decline in June and July, which are the rainiest months. At the same time, majority of plantation crops are likely to benefit due to increase in rainfall during the post-monsoon season if they are stable and prolonged.

Keywords: Man-Kendall rank statistics; Trends; Coefficient of variation; Southwest monsoon
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