Atmospheric Environment (v.40, #13)

Haagen-smit Prize 2005 (2245-2247).

We describe the development and evaluation of a computationally efficient new multicomponent aerosol dynamics model that simulates the full aerosol size distribution and composition starting at a diameter of 0.8 nm. The model uses a recently developed ternary (sulfuric acid–ammonia–water) nucleation parameterization and a two-moment sectional algorithm, simulating both the aerosol number and mass distributions. Three chemical components, sulfate, ammonium, and non-volatile organics are simulated. The model is evaluated first against analytical solutions of the coagulation and condensation equations and then against ambient measurements from the Pittsburgh Air Quality Study. The model is able to reproduce nucleation events from their start to completion. The simulations suggest that ammonia availability controls the nucleation bursts in the northeastern US. The first stage of the nucleation event in that area is the nucleation burst with growth of neutral ultrafine particles. In a second stage, the gas phase ammonia concentration approaches zero, the nucleation burst stops and the ultrafine particles become acidic growing by condensation of sulfuric acid. The present model is thirty times faster than comparable high-resolution models of aerosol dynamics and nucleation.
Keywords: Ternary nucleation; Aerosol acidity; Modeling;

Seasonal abundance of organic molecular markers in urban particulate matter from Philadelphia, PA by Min Li; Stephen R. McDow; David J. Tollerud; Monica A. Mazurek (2260-2273).
Organic molecular markers were measured in airborne particulate matter (PM10) from the City of Philadelphia North Broad Street air quality monitoring site to identify the seasonal abundance of key tracer compounds together with their dominant sources. Daily PM10 samples were collected seasonally in 2000 for four 2-week periods (January, April, August, and October). The North Broad Street site is within a heavily populated location in Philadelphia, PA. A suite of 52 individual organic marker compounds was monitored in the PM10 samples. Molecular markers, homologous compound series, and nonpolar and polar organic compounds were detected at ng m−3 ambient concentrations using gas chromatography/ion trap mass spectrometry (GC/IT MS). Organic diacids (C3–C9) and monoacids (C10–C30) had seasonal mass concentrations ranging from 91.0 (winter) to 261.8 ng m−3 (summer). Total n-alkanes (C25–C33) ranged from 25.9 (spring) to 49.5 ng m−3 (fall), total PAHs from 2.1 ng m−3 (summer) to 4.1 ng m−3 (winter), and total hopanes ranged from 4.0 ng m−3 (winter) to 7.4 ng m−3 (fall). The molecular marker ambient mass concentrations were normalized by the annual average mass of PM10 elemental carbon (EC) for the central Philadelphia area. The ambient mass concentrations to EC and OC ratios ranged from 2.6×10−3 for total PAHs to EC to 115.3×10−3 for total n-alkanoic acids to EC, 0.5×10−3 for total PAHs to OC to 23.8×10−3 for total n-alkanoic acids to OC. Ambient concentrations of individual markers are similar to other reported levels for metropolitan Los Angeles, CA and Atlanta, GA. Seasonal and daily variations of marker compounds are consistent with motor vehicle exhaust, particularly in winter. Summer concentration patterns indicate the importance of secondary organic aerosol to the PM10 ambient mass.
Keywords: Particulate matter (PM); Organic; Ambient concentration; Gas chromatography/mass spectrometry; Philadelphia;

Assessment of schoolchildren's exposure to traffic-related air pollution in the French Six Cities Study using a dispersion model by Céline Pénard-Morand; Charles Schillinger; Alexandre Armengaud; Ginette Debotte; Eve Chrétien; Serge Pellier; Isabella Annesi-Maesano (2274-2287).
The purpose of this work was to estimate exposure to traffic-related air pollution (TAP), of the 6683 schoolchildren included in a cross-sectional epidemiological study conducted in six French cities to determine the effects of urban air pollution (AP) on respiratory and allergic health.Annual mean concentrations of benzene, CO, NO2, NO x , PM10 and SO2 were calculated, in front of the 108 schools attended by the children, by the validated STREET 5 software, which combines data on regional and local components of AP. STREET contains a database of emissions estimated by the IMPACT 2.0 software developed by ADEME-France and results of ambient concentrations modelled by the WinMISKAM 4.2 dispersion model. The input data required were background AP, traffic conditions (daily traffic density; average speed; percentage of gridlocks and proportion of each type of vehicle) and dispersion conditions (topography of the street segments modelled and meteorology).Emissions of air pollutants in front of the 108 schools were considerably scattered. Calculated concentrations (μg m−3) also varied considerably at: [1.0–5.1] for benzene, [303.8–988.1] for CO, [17.8–78.9] for NO2, [23.3–195.2] for NO x , [10.0–52.0] for PM10 and [2.4–16.4] for SO2. About 64% (29%, respectively) of the schools had annual mean concentrations of NO2 (PM10, respectively) exceeding the European quality objectives (40 and 30 μg m−3, respectively).These exposure indicators, capable of identifying small area variations in AP contrary to surrogate measures usually used in epidemiology, will enable better studies on the impact of urban AP on health.
Keywords: Traffic-related air pollution; Exposure assessment; Dispersion model; Respiratory and allergic health; Epidemiology;

US Environmental Protection Agency estimates of on-road vehicle emissions are compared with ambient measurements and a fuel-based emission inventory. Several significant weaknesses and strengths are identified. (1) The emission estimates have varied considerably over the past 15 years and are not clearly converging to progressively more accurate and certain results. (2) The most recent emissions estimate accurately captures the rapid decrease in carbon monoxide (CO) and volatile organic compounds (VOC) emissions, but overestimates the magnitude of CO emissions by about a factor of two. (3) The oxides of nitrogen (NO x ) emission estimates for the mid to late 1990s are reasonably accurate, but NO x emissions have increased through that decade rather than decreased as indicated in emission estimates. (4) The most recent emissions estimate more accurately apportions NO x emissions between diesel and gasoline fueled vehicles than did earlier reports. (5) The ratio of two specific VOC species that has been characterized by ambient measurements suggests that the inventory speciation of the VOCs is inaccurate by factors of 3–4. These tests lead to the derivation of “inferred emissions” for CO and NO x from the US on-road vehicle fleet that are consistent with all information used in these tests. Finally, it is shown that the international picture of US emissions has significant inaccuracies and inconsistencies.
Keywords: Carbon monoxide; Nitrogen oxides; NO x ; Hydrocarbons; VOC;

Volatile organic compound emission factors from roadside measurements by Hiroto Kawashima; Shigeki Minami; Yoshimichi Hanai; Akihiro Fushimi (2301-2312).
Volatile organic compounds (VOCs) play a significant role in the generation of urban photochemical smog. In addition, some VOCs, such as benzene, are harmful to human health. In Japan, motor vehicles are the dominant source of VOCs. Therefore, it is important to determine the emission of VOCs from vehicles in order to estimate human risk and the production mechanisms of photochemical smog. In this study, we estimated emission factors with a methodology that considered the following points: (1) real-world emissions, (2) individual VOCs, (3) low vehicle speeds, (4) low investigation cost, and (5) user-friendly methodology.Samples were collected approximately 5 m from each side of National Route No. 467 in Kanagawa Prefecture, Japan. Sampling consisted of twelve 1-h sampling periods at three points on three dates: 21 February 2003 (7:00–19:00), 13 May 2003 (7:00–19:00), and 13 September 2003 (8:00–20:00). The samples were analyzed using GC/FID and GC/MS. In addition, information on vehicle types, traffic volumes, and weather conditions was collected from beside the road. Emission factors of individual VOCs were estimated from the measured data by running the CALINE4 dispersion model as an inverse model.The average speed of all vehicles was 22 km h−1; 81.3% of all vehicles were light-duty vehicles, 12.3% were heavy-duty vehicles, and 6.5% were motorcycles. We estimated the emission factors of 34 individual VOCs. The emission factors for all vehicles combined averaged over all sampling days ranged from 0.25 to 51 mg vehicle−1  km−1. The emission factors of benzene and toluene were 5.2 and 17 mg vehicle−1  km−1, respectively. In addition, the estimated emission factors were compared with those estimated from other recent studies. The emission factors for light-duty vehicles (LDVs), heavy-duty vehicles (HDVs), and motorcycles separately were also estimated by using a non-negative least squares method. However, these emission factors were found to be unreliable for the current sample size; therefore, the sample size needed to estimate reliable emission factors was calculated.
Keywords: Volatile organic compounds; Emission factors; Vehicle emissions; Roadside measurement; CALINE4;

Diesel emission improvements by the use of oxygenated DME/diesel blend fuels by Wang Ying; Zhou Longbao; Wang Hewu (2313-2320).
A kind of oxygenate fuel, DME, has been proposed and tested for use with diesel fuel as a means of reducing exhaust emissions. The addition of DME to diesel fuel results in the decrease of the lower calorific value, aromatics fraction and kinematic viscosity of blend fuels. Simultaneously, cetane number, C/H ratio and oxygen content of the blends are enhanced, which has some favorable effects on the combustion and emission of the blends with 10%, 20% and 30% DME by mass. The study on the performance and emissions of the diesel/DME blend is conducted in a DI engine. The emission characteristics of four fuels are determined in a diesel engine. At high loads, the blends reduce smoke significantly with a little penalty on CO and HC emissions compared to diesel fuel. NO x and CO2 emissions of the blends are decreased somewhat. At low loads, the blends have slight effects on smoke reduction due to overall leaner mixture. The results indicate the potential of diesel reformation for clean combustion in diesel engines.
Keywords: Diesel engine; DME; Oxygen content; Emission; BMEP;

This study uses an improved emission inventory model to assess the uncertainties in emissions of dioxins and furans associated with both knowledge on the exact technologies and processes used, and with the uncertainties of both activity data and emission factors. The annual total emissions for the year 2000 in 13 countries in central and eastern Europe can be estimated with 90% confidence within a range that is about a factor of 2–3 lower to a factor of 3–5 higher than a point value obtained from a more classical approach. It is also shown that the contribution of small residential sources and larger industrial installations and processes are of the same order of magnitude in these countries. It is argued that, despite these uncertainties, policy options can be evaluated and policy decisions on abatement of dioxin and furan emissions can be made. Dioxins and furans belong to the persistent organic pollutants (POPs), an important group of air pollutants that can have long-term effects on ecosystems and human health. Emission estimates for these pollutants all suffer from high uncertainties. This study shows that policy conclusions can still be derived despite these high uncertainties.
Keywords: Uncertainty; Air emissions; Dioxins/furans; Policy implications;

Analysis of heavy-duty diesel truck activity and emissions data by Tao Huai; Sandip D. Shah; J. Wayne Miller; Ted Younglove; Donald J. Chernich; Alberto Ayala (2333-2344).
Despite their relatively small population, heavy-duty diesel vehicles (HDDVs) are (in 2005) disproportionate contributors to the emissions inventory for oxides of nitrogen (NO x ) and particulate matter (PM) due to their high individual vehicle emissions rates, lack of engine aftertreatment, and high vehicle miles traveled. Beginning in the early 1990s, heavy-duty engine manufacturers began equipping their engines with electronic sensors and controls and on-board electronic computer modules (ECMs) to manage these systems. These ECMs can collect and store both periodic and lifetime engine operation data for a variety of engine and vehicle parameters including engine speed and load, time at idle, average vehicle speed, etc.The University of California, Riverside (UCR), under a contract with the California Air Resources Board (CARB), performed data analysis of 270 ECM data sets obtained from the CARB. The results from this analysis have provided insights into engine/vehicle operation that have not been obtained from previous on-board datalogger studies since those previous studies focused on vehicle operation and did not collect engine operating data.Results indicate that HDDVs spend a considerable amount of time at high-speed cruise and at idle and that a smaller percentage of time is spent under transient engine/vehicle operation. These results are consistent with other HDDV activity studies, and provide further proof of the validity of assumptions in CARB's emission factor (EMFAC2002) model. An additional important contribution of this paper is that the evaluation of vehicle ECM data provides several advantages over traditional global positioning system (GPS) and datalogger studies: (1) ECM data is significantly cheaper than the traditional method ($50 record–1 vs. ∼$2000 record–1) and (2) ECM data covers vehicle operation over the entire life of the vehicle, whereas traditional surveys cover only short periods of surveillance (days, weeks, or months). It is worthwhile to note that this work was not intended to compare the various methods of data collection but to provide additional empirical support for the EMFAC2002 model and to explore the utility of this unique low-cost form of data collection and analysis.
Keywords: Heavy-duty diesel; Vehicle activity; ECM; NO x emissions; Driving activities; Emissions estimate;

Identification of major sources of airborne pollutants and their contribution to pollutant loadings are critical in developing effective pollution control and mitigation strategies. In this study, a comprehensive dataset of non-methane volatile organic compounds (NMVOCs) collected from August 2001 to December 2002 at a polluted rural/coastal site in the Pearl River Delta (PRD) is analyzed to assess the relative contributions of major pollution sources to ambient NMVOC mixing ratios. A unique approach based on emission ratios of individual chemical species was used to classify the bulk air samples in order to apportion regional and local source contributions to the measured mixing ratios. The collected air samples fell into four major groups, including air masses from the inner PRD region and Hong Kong (HK) urban area. To estimate the source apportionment of NMVOCs, a principal component analysis/absolute principal component scores receptor model was applied to the classified data points. The results indicate that the regional and local source contributions to ambient NMVOC levels at the site were significantly different due to the differences in local versus regional energy use and industrial activities. For air masses originating from HK, vehicular emissions accounted for approximately 39% of the total NMVOC levels, followed by industrial emissions (35%), gasoline evaporation (14%) and commercial/domestic liquefied petroleum gas/natural gas use (12%). By contrast, for air masses originating from the PRD the industrial emissions accounted for 43% of the total NMVOC burden, followed by vehicular emissions (32%) and biomass burning (25%). In particular, the higher regional contribution of biomass burning found in this study as compared to existing emission inventories suggests that further efforts are necessary to refine the emission inventories of NMVOCs in the PRD region.
Keywords: Non-methane volatile organic compounds; Source apportionment; PCA/APCS; Pearl River Delta; Hong Kong;

Model study on acidifying wet deposition in East Asia during wintertime by Zhiwei Han; Hiromasa Ueda; Tatsuya Sakurai (2360-2373).
A regional air quality model (RAQM) has been developed and applied together with an aerosol model to investigate the states and characteristics of wet deposition in East Asia in December 2001. Model simulation is performed with monthly based emission inventory [Streets, D.G., Bond, T.C., Carmichael, G.R., Fernandes, S.D., Fu, Q., He, D., Klimont, Z., Nelson, S. M., Tsai, N.Y., Wang, M.Q., Woo, J.-H., Yarber, K.F., 2003. An inventory of gaseous and primary emissions in Asia in the year 2000. Journal of Geophysical Research 108(D21), 8809] and meteorological fields derived from MM5. Model results are compared with extensive monitoring data including relevant gaseous species and ions in precipitation. The validation demonstrates that this model system is able to represent most of the major physical and chemical processes involved in acid deposition and reproduces concentrations reasonably well, within a factor of 2 of observations in general. The study shows that the regions with pH less than 4.5 are mainly located in southwestern China, parts of the Yangtze Delta, the Yellow Sea and the Korean peninsula, indicating wide regions of acid precipitation in East Asia in wintertime. Japan islands mainly exhibit pH values of 4.5–5.0, whereas over wide areas of northern China, pH values are relatively high (⩾5.0) due to neutralization by alkaline materials such as calcium-laden particles and ammonia, which are more abundant in northern China than that in southern China. While acid rain over most of China is still characterized by sulfur-induced type, considerable areas of eastern China and the western Pacific Rim are found to be more affected by nitric acid than sulfuric acid in acidification of precipitation, which is supposed to result from a combined effect of variations in photochemistry and emission, suggesting the increasing importance of NO x emission in these regions.
Keywords: Acid deposition; Numerical study; NO3 /nssSO4 2− ratio in precipitation; Precipitation chemistry; Trend of emission;

Atmospheric concentrations of oxygenated polycyclic aromatic hydrocarbons (Oxy-PAHs) in Santiago de Chile city were evaluated to study particulate Oxy-PAHs profiles during cold and spring weather periods. Samples of urban particulate matter PM10 were collected during July and September–October, using a high volume air sampler provided with glass fiber filters. Samples were analyzed by gas chromatography-mass spectrometry (GC-MS). Ketones, quinones, aldehydes and carboxaldehydes were characterized and quantified.Among 12 oxy-PAHs found in the air samples, 1-pyrenecarboxaldehyde was found the greatest amount at the two sampling seasons (winter and spring) and at the two sampling sites (4.66±4.21 ng m−3 at Providencia and 2.66±2.33 ng m−3 at Las Condes, during winter). Concentration of these carcinogenic compounds is higher than other cities indicating an exposure of the inhabitants of Santiago to high amount of carcinogenic-mutagenic compounds air pollutants.
Keywords: Oxy-PAHs; Santiago de Chile; PM10; Particulate matter;

Hourly concentrations of ambient volatile organic compounds (VOCs) were analyzed between June and October 2003 at three sites, in order to further understand emissions of VOCs in the Houston area. Ambient concentrations of 54 VOCs from three monitoring sites in the heavily industrialized Houston Ship Channel were analyzed using positive matrix factorization (PMF). Hourly concentrations were divided into weekly data sets and analyzed to determine the most important source types that contribute to the measured VOC concentrations at these three sites. For each monitoring site, three or four sources were identified for each week as major contributors to ambient VOC concentrations using PMF. The sources isolated by the model are consistent with the chemical compositions of refinery, petrochemical and evaporative emissions, which are also the dominant inventoried sources of VOCs in Houston Ship Channel region. A night-time data analysis was also performed at two sites to investigate the effect of photochemical reactions on source attribution of VOCs.
Keywords: Positive matrix factorization; NMHC; Ozone; Source apportionment; Night-time analysis;

Approximating dispersion from a finite line source by Akula Venkatram; T.W. Horst (2401-2408).
We examine the basis of the approximation suggested by Calder [1973. On estimating air pollution concentrations from a highway in an oblique wind. Atmospheric Environment 7, 863–868], Luhar and Patil [1989. A general finite line source model for vehicular pollution prediction. Atmospheric Environment 23, 555–562], and Esplin [1995. Approximate explicit solution to the general line source problem. Atmospheric Environment 29, 1459–1463] for the concentration downwind of a finite line source when the wind blows at an angle to the source. The Luhar–Esplin (LE) approximation is equivalent to replacing the varying source–receptor distances in the integral representing the concentration caused by the line source by an effective distance along the wind direction between the receptor and the line source. This approximation performs poorly when the wind approaches a direction parallel to the line source. It can be improved by retaining the effective-distance approximation only for evaluation of vertical diffusion and approximating the resulting line source integral with the assumption of small cross-wind distance. The resulting Horst–Venkatram approximation has much smaller errors than those of the LE approximation for the range of receptor locations considered in this paper.
Keywords: Line source; Finite line source; Highway dispersion; Area sources; Approximate integrals;

Enhanced water vapor in Asian dust layer: Entrainment processes and implication for aerosol optical properties by Soon-Chang Yoon; Sang-Woo Kim; Jiyoung Kim; Byung-Ju Sohn; Anne Jefferson; Suk-Jin Choi; Dong-Hyun Cha; Dong-Kyou Lee; Theodore L. Anderson; Sarah J. Doherty; Rodney J. Weber (2409-2421).
The entrainment process of water vapor into the dust layer during Asian dust events and the effect of water vapor associated with the Asian dust layer (ADL) on aerosol hygroscopic properties are investigated. The entrainment processes of water vapor into the ADL is examined by using a PSU/NCAR MM5 together with the backward trajectory model, radiosonde data, and remotely sensed aerosol vertical distribution data. Two dust events in the spring of 1998 and 2001 are examined in detail. The results reveal that the water vapor mixing ratio (WVMR) derived by the MM5 fits in well with the WVMR observed by radiosonde, and is well coincident with the aerosol extinction coefficient (σ ep) measured by the micro-pulse lidar. The temporal evolution of the vertical distributions of WVMR and σ ep exhibited similar features. On the basis of a well simulation of the enhanced water vapor within the dust layer by the MM5, we trace the dust storms to examine the entrainment mechanism. The enhancement of WVMR within the ADL was initiated over the mountainous areas. The relatively moist air mass in the well-developed mixing layer over the mountainous areas is advected upward from the boundary layer by an ascending motion. However, a large portion of the water vapor within the ADL is enhanced over the edge of a highland and the plains in China. This is well supported by the simulated WVMR and the wind vectors. Aircraft-based in situ measurements of the chemical and optical properties of aerosol enable a quantitative estimation of the effect of the enhanced WVMR on the aerosol hygroscopic properties. The submicron aerosol accompanied by the dust storm caused an increase of aerosol scattering through water uptakes during the transport. This increase could be explained by the chemical fact that water-soluble submicron pollution aerosols are enriched in the ADL.
Keywords: Entrainment process of water vapor; Asian dust; PSU/NCAR MM5; Aerosol light scattering hygroscopic growth; Water-soluble submicron pollution aerosols;