Atmospheric Environment (v.38, #16)

Currently used models for dispersion in the surface layer are explicitly based on Monin–Obukhov (M–O) theory. Because M–O variables such as the surface friction velocity and M–O length are not always accessible or M–O similarity might not hold at the site of interest, there is a need for a model that uses alternative meteorological inputs. Here, we examine the use of near-surface profiles of turbulence and wind speeds instead of M–O variables. We use data from the Prairie Grass experiment (1958, Project Prairie Grass, a field program in diffusion, Vol. 1, Geophysics Research Paper No. 59. Air Force Cambridge Research Center, Bedford, MA) because of its completeness in terms of meteorological inputs as well as spatial coverage of concentration measurements. The maximum surface concentrations and the crosswind plume spreads are first explained using an M–O theory-based model proposed by van Ulden (1978, Simple estimates for vertical dispersion from sources near the ground. Atmospheric Environment 12, 2125–2129), whose performance has already been documented in the literature. The performance of this model is compared with those of models using alternative meteorological inputs. The results from the study indicate that, under stable conditions, models that use profiles of winds and turbulence do not perform as well as van Ulden's model. On the other hand, under unstable conditions, the differences in model performance are much smaller. This supports other studies that indicate that relatively simple dispersion models can be used to estimate concentrations in urban areas, where the boundary layer is often unstable even during the night.
Keywords: Dispersion; Surface releases; Similarity theory; Micrometeorological measurements; Model performance; Urban dispersion; Prairie Grass experiment;

Dry deposition fluxes and velocities of polychlorinated biphenyls (PCBs) associated with particles by Yücel Tasdemir; Mustafa Odabasi; Nedim Vardar; Aysun Sofuoglu; Thomas J. Murphy; Thomas M. Holsen (2447-2456).
The interest in atmospheric deposition by the scientific community has increased a great deal over the past several years because of its significant contribution to the pollution budget of many natural waters. Dry deposition is an effective removal mechanism for polychlorinated biphenyls (PCBs) from the atmosphere. This study focuses on the understanding of the particulate dry deposition of PCBs in urban areas. In this paper, 43 chromatographic PCB congener peaks which represent 50 individual or coeluting congeners were evaluated.The PCB dry deposition fluxes were measured using a smooth, greased, knife-edge surrogate surface holding greased Mylar strips in Chicago, IL. The average PCB dry deposition flux measured (190±80 ng m−2  day−1) was similar to those measured in other urban areas. Ambient air samples were also collected simultaneously with flux samples. The average apparent dry deposition velocity, calculated by dividing the fluxes to the particle phase concentrations was 5.2±2.9 cm s−1. This value is in good agreement with the values calculated using similar techniques.
Keywords: PCBs; Dry deposition; Particle deposition; Deposition velocity; Surrogate surface;

Fumigants are used to enhance the yield and quality of agricultural produce, which is critical to the maintenance of the production levels of carrots, potatoes, tomatoes, strawberries, melons, and many other crops grown in the US and throughout much of the world. With the worldwide phase-out of methyl bromide in progress, the continued availability of the remaining alternatives, such as metam-sodium, 1,3-dichloropropene, and chloropicrin, is becoming increasingly important. Metam-sodium has been used for over 40 years and is the second most widely used fumigant in the United States. Reduction in off-gassing rates of fumigants can promote health and safety benefits and an increased dose in the treatment zone, thereby increasing the potential efficacy of these products. On this basis, there is a need to evaluate off-gassing rates as a function of application and sealing methods. This paper summarizes recent research into the volatilization of the principal transformation product of metam-sodium, i.e., methyl isothiocyanate (MITC), into the atmosphere as a function of application and sealing methods. Seven field studies were conducted from 1999–2001 to evaluate the off-gassing rates of MITC from applications of metam-sodium by shank injection and chemigation using two different water sealing methods, i.e., standard water sealing and intermittent water sealing. MITC is slightly soluble in water. Irrigation of a field following an application helps to retain the compound in the soil, minimizing off-gassing while increasing the dose to the target pests. Intermittent water sealing involves applying water on an intermittent basis to minimize off-gassing rates during nighttime periods when relatively poor atmospheric dispersion conditions often occur. Research conducted by the Metam-Sodium TASK Force indicates that intermittent water sealing significantly reduces off-gassing rates both for shank injection and chemigation applications when compared with standard water sealing practices.
Keywords: Metam-sodium; MITC; Shank injection; Chemigation; Water sealing; ISCST3; Method of least squares; TOXST; Fumigants; Pesticide; Application; Agriculture; Normalized modeling; Emission fitting; Ambient monitoring;

Fumigants, such as metam-sodium, can help control pests in the soil and improve the quality and yields for a wide range of crops. Enhanced control of field loss, or off-gassing, to the atmosphere is an important means of promoting fumigant efficacy and sound environmental management of fumigants. Metam-sodium has been used for over 40 years and is one of the most widely used fumigants in the United States. This paper describes a modeling method, the fumigant emissions modeling system (FEMS), which was developed to promote more realistic assessment of downwind concentrations in the vicinity of an applied field. Two models of the US Environmental Protection Agency, i.e., the industrial source complex short-term (ISCST3) model and the toxic modeling system short-term (TOXST) model are used, in conjunction with a pre-processing program, PCRAMMET, and the FEMS programming code to provide a Monte Carlo treatment for all key model inputs. Start times for applications are triggered on a Monte Carlo basis consistent with the annual application frequency. Typically, 1000–10,000 years of applications are simulated, outputting data to display average exceedances per year of selected concentration endpoints as a function of distance from the edge of the treatment zone. A sensitivity analysis is displayed for key meteorological variables, showing uncertainty in emission rates to be a significant input parameter. Some comparisons also are made between ambient concentrations and modeled personal and indoor exposures, showing perspective on the benefits of the indoor environment to buffer peak concentrations.
Keywords: Monte Carlo; Dispersion modeling; Randomization; Uncertainty; Metam-sodium; Methyl isothiocyanate; ISCST3; TOXST; Fumigants; Pesticide; Air quality; Agriculture; Exposure assessment;

Sorption of organic gases in a furnished room by Brett C. Singer; Kenneth L. Revzan; Toshifumi Hotchi; Alfred T. Hodgson; Nancy J. Brown (2483-2494).
We present experimental data and semi-empirical models describing the sorption of organic gases in a simulated indoor residential environment. Two replicate experiments were conducted with 20 volatile organic compounds (VOCs) in a 50-m3 room finished with painted wallboard, carpet and cushion, draperies and furnishings. The VOCs span a wide volatility range and include ten hazardous air pollutants. VOCs were introduced to the static chamber as a pulse and their gas-phase concentrations were measured during a net adsorption period and a subsequent net desorption period. Three sorption models were fit to the measured concentrations for each compound to determine the simplest formulation needed to adequately describe the observed behavior. Sorption parameter values were determined by fitting the models to adsorption period data then checked by comparing measured and predicted behavior during desorption. The adequacy of each model was evaluated using a goodness of fit parameter calculated for each period.Results indicate that sorption usually does not greatly affect indoor concentrations of methyl-tert-butyl ether, 2-butanone, isoprene and benzene. In contrast, sorption appears to be a relevant indoor process for many of the VOCs studied, including C8–C10 aromatic hydrocarbons (HC), terpenes, and pyridine. These compounds sorbed at rates close to typical residential air change rates and exhibited substantial sorptive partitioning at equilibrium. Polycyclic aromatic HCs, aromatic alcohols, ethenylpyridine and nicotine initially adsorbed to surfaces at rates of 1.5–>6 h−1 and partitioned 95–>99% in the sorbed phase at equilibrium.
Keywords: Volatile organic compounds; Adsorption; Desorption; Residential; Indoor air quality; Hazardous air pollutants; Tobacco smoke tracers;

Qualitative and quantitative evaluation of MODIS satellite sensor data for regional and urban scale air quality by Jill A. Engel-Cox; Christopher H. Holloman; Basil W. Coutant; Raymond M. Hoff (2495-2509).
Advances in satellite sensors have provided new datasets for monitoring air quality at urban and regional scales. Qualitative true color images and quantitative aerosol optical depth data from the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on the Terra satellite were compared with ground-based particulate matter data from US Environmental Protection Agency (EPA) monitoring networks covering the period from 1 April to 30 September, 2002. Using both imagery and statistical analysis, satellite data enabled the determination of the regional sources of air pollution events, the general type of pollutant (smoke, haze, dust), the intensity of the events, and their motion. Very high and very low aerosol optical depths were found to be eliminated by the algorithm used to calculate the MODIS aerosol optical depth data. Correlations of MODIS aerosol optical depth with ground-based particulate matter were better in the eastern and Midwest portion of the United States (east of 100°W). Data were patchy and had poorer correlations in the western US, although the correlation was dependent on location. This variability is likely due to a combination of the differences between ground-based and column average datasets, regression artifacts, variability of terrain, and MODIS cloud mask and aerosol optical depth algorithms. Preliminary analysis of the algorithms indicated that aerosol optical depth measurements calculated from the sulfate-rich aerosol model may be more useful in predicting ground-based particulate matter levels, but further analysis would be required to verify the effect of the model on correlations. Overall, the use of satellite sensor data such as from MODIS has significant potential to enhance air quality monitoring over synoptic and regional scales.
Keywords: Air quality; Satellite; MODIS; Particulate matter; Policy;

Short-term measurements of CO, NO, NO2, organic compounds and PM10 at a motorway location in an Austrian valley by J. Beauchamp; A. Wisthaler; W. Grabmer; C. Neuner; A. Weber; A. Hansel (2511-2522).
In situ measurements of CO, NO x , PM10 and certain organic compounds took place over an 11 day period encompassing a 12 h motorway blockade. Located within the Inn valley (Tirol, Austria), the monitoring site experiences varying meteorological conditions and traffic frequency throughout the day which both strongly influence air pollutant levels. Early morning increases of NO x , PM10 and aromatic hydrocarbons were clearly correlated with rising traffic. Midday minima and afternoon maxima may be explained by changing wind conditions and varying inversion layer dynamics. Night time lows in concentrations can be explained by minimal traffic activity. Classification of compound sources was made through grouping of data, separated into times when heavy duty vehicles (HDV) were permitted to use the motorway and HDV-ban periods. Increased levels of NO x and PM10 were observed from data that included periods of high HDV numbers, with levels decreasing significantly during HDV-ban periods. In contrast, the aromatic hydrocarbons and CO displayed only minor variations between these two periods. Furthermore, on typical workdays NO x levels reached a maximum that corresponded to a peak in HDV numbers, whereas the aromatic compounds peaked later when LDV numbers had reached their maximum. Our findings give strong evidence that increased NO x and PM10 levels can be predominantly attributed to HDV traffic. Principal components analyses for the separated data further support this conclusion.
Keywords: Vehicle emissions; Mountain valley meteorology; PTR-MS; Benzene; NO x and PM10;

Measurements of VOCs in Mexico City (1992–2001) and evaluation of VOCs and CO in the emissions inventory by J.L. Arriaga-Colina; J.Jason West; G. Sosa; S.S. Escalona; R.M. Ordúñez; A.D.M. Cervantes (2523-2533).
Measurements of ambient volatile organic compounds (VOCs) are reported from several field campaigns of simultaneous measurements in the Mexico City Metropolitan Area (MCMA). Conducted between 1992 and 2001, these measurements represent the longest and most complete record of VOC measurements available for Mexico City. Ambient air VOC samples were collected at surface air quality monitoring sites in electro-polished stainless-steel canisters, and analyzed by Gas Chromatography with Flame Ionization Detection for the C2 to C12 hydrocarbons and MTBE. This paper presents the total VOCs in morning measurements (06:00–09:00 AM) and its trend through time. Average concentrations of total VOCs in each campaign were between 3130 and 6711 ppbC at Xalostoc (northeast of the city center), 2994 and 4935 ppbC at La Merced (center), and 1136 and 2815 ppbC at Pedregal (southwest). A linear regression of the total VOCs reveals a slight decreasing trend from 1992 to 2001 which is statistically significant only at Xalostoc; the decreasing trends at the two other sites are not statistically significant and therefore inconclusive. This apparent stabilization and possible decrease in ambient concentrations, despite the growth in the vehicular fleet and other activities during this period, suggests that VOC emission control measures have been effective at reducing emissions. Co-located measurements of CO and NO x from the Metropolitan Atmospheric Monitoring Automatic Network are used to calculate ratios of total VOCs/NO x and CO/NO x , in order to evaluate the official 1998 emissions inventory for the MCMA. The ambient ratios of VOCs/NO x and CO/NO x are found to be factors of 2–3 times higher than the corresponding inventory ratios. This discrepancy suggests that VOC and CO emissions may be significantly underestimated.
Keywords: Volatile organic compounds; VOC/NO x ratio; CO/NO x ratio; Mexico City;

Measurement of PCDD/F congener distributions in MWI stack gas and ambient air in northern Taiwan by Moo Been Chang; Kai Hsien Chi; Shu Hao Chang; Yuan Wu Chen (2535-2544).
To meet the emission standards that become more and more stringent, the waste incinerators are commonly equipped with various air pollution control devices. Gas/particulate phase distribution of polychlorinated dibenzo-p-doxin and furan (PCDD/F) in stack gas could be much different when different control technologies are applied. This study evaluates PCDD/F congener distributions at the stack gas of a municipal waste incinerator (MWI) and ambient air in northern Taiwan via stack gas and ambient air sampling and analysis. Ambient air samples were taken in the vicinity area of a large-scale MWI for measuring PCDD/F concentrations and partitioning gas/particulate phase from November 1999 through January 2001. Stack gas samples of the MWI were taken during the period of ambient air sampling. The PCDD/F concentrations measured in fall and winter seasons are significantly higher than those measured in summertime. In addition, the results obtained on gas/particulate partitioning of ambient air samples indicate that the particulate-phase PCDD/Fs account for more than 80% of the total concentration. Nevertheless, the gas/particulate partitioning of stack gas PCDD/F sample was completely different from that of the ambient air samples. The gas-phase PCDD/Fs account for more than 85% of the total concentration in MWI stack gas. This study also indicates that as the chlorination level of PCDD/F congeners increases, the percentage of PCDD/Fs existing in gas phase decreases in either ambient air or stack gas of MWI. Furthermore, the temperature in ambient air also affects the percentage of particle-bound dioxins. As the ambient air temperature decreases by 10°C, the percentage of PCDD/Fs in particulate phase increases around 20%. PCDFs account for about 80% of the I-TEQ concentrations for stack gas and ambient air sample, among them the 2,3,4,7,8-PeCDF is the major contributor, accounting for 30–55% of the total I-TEQ.
Keywords: Dioxin; Incinerator; Atmosphere; Sampling; Gas/particle phase;

Particle-bound aliphatic and polycyclic aromatic hydrocarbons (AHs and PAHs, respectively) were determined in the ambient air of the Eordea basin, in western Greece, where intensive coal burning for power generation takes place. Thirteen PAHs, n-alkanes (C14–C35), hopanes, and isoprenoid hydrocarbons (pristane and phytane) were determined in the total suspended particles collected from the atmosphere of four sites within the basin receiving potential impacts from various sources, such as fly ash, coal mining, automobile traffic, domestic heating, and agricultural or refuse burning. The same organic species were also determined in the fly ash generated in power stations, and in particulate emissions from open burning of biomass (dry corn leaves) and refuse burning. Organic particle sources were resolved using concentration diagnostic ratios and factor analysis (FA). A multivariate statistical receptor model (Absolute Principal Component Analysis, APCA) was finally employed to estimate the contribution of identified sources to the measured concentrations of organic pollutants. Four major sources for ambient PAHs and AHs were identified displaying variable contribution in different sites: (a) fossil fuel combustion, (b) biogenic emissions, (c) refuse burning, and (d) oil residues. Fuel combustion was the major source of ambient PAHs and an important source of n-alkanes in the range C21–C28. Oil residues were found to be the major source of low molecular weight n-alkanes (particularly the C14–C16), and an important source of pristane, phytane and UCM. Biogenic sources were primarily responsible for the high molecular weight n-alkanes explaining almost the entire concentration levels of homologues >C32. Biomass burning was particularly important for the C23–C26 n-alkanes. Despite the vicinity of certain sampling sites to power stations, coal fly ash was not identifiable as a source for ambient PAHs and AHs.
Keywords: Atmospheric particulate matter; Fly ash; Hopanes; n-alkanes; Phytane; Polycyclic aromatic hydrocarbons; Power generation; Pristane;

A European aerosol phenomenology—1: physical characteristics of particulate matter at kerbside, urban, rural and background sites in Europe by Rita Van Dingenen; Frank Raes; Jean-P Putaud; Urs Baltensperger; Aurélie Charron; M.-Cristina Facchini; Stefano Decesari; Sandro Fuzzi; Robert Gehrig; Hans-C Hansson; Roy M Harrison; Cristoph Hüglin; Alan M Jones; Paolo Laj; Gundi Lorbeer; Willy Maenhaut; Finn Palmgren; Xavier Querol; Sergio Rodriguez; Jürgen Schneider; Harry ten Brink; Peter Tunved; Kjetil Tørseth; Birgit Wehner; Ernest Weingartner; Alfred Wiedensohler; Peter Wåhlin (2561-2577).
This paper synthesizes data on aerosol (particulate matter, PM) physical characteristics, which were obtained in European aerosol research activities at free-troposphere, natural, rural, near-city, urban, and kerbside sites over the past decade. It covers only two sites in the semi-arid Mediterranean area, and lacks data from Eastern Europe. The data include PM10 and/or PM2.5 mass concentrations, and aerosol particle size distributions. Such data sets are more comprehensive than those currently provided by air quality monitoring networks (e.g. EMEP, EUROAIRNET). Data available from 31 sites in Europe (called “The Network”) were reviewed. They were processed and plotted to allow comparisons in spite of differences in the sampling and analytical techniques used in various studies. A number of conclusions are drawn as follows:Background annual average PM10 and PM2.5 mass concentrations for continental Europe are 7.0±4.1 and 4.8±2.4 μg m−3, respectively.The EU 2005 annual average PM10 standard of 40 μg m−3 is exceeded at a few sites in The Network. At all near city, urban and kerbside sites, the EU 2010 annual average PM10 standard of 20 μg m−3, as well as the US-EPA annual average PM2.5 standard of 15 μg m−3 are exceeded. In certain regions, PM10 and PM2.5 in cities are strongly affected by the regional aerosol background.There is no “universal” (i.e. valid for all sites) ratio between PM2.5 and PM10 mass concentrations, although fairly constant ratios do exist at individual sites. There is no universal correlation between PM mass concentration on the one hand, and total particle number concentration on the other hand, although a ‘baseline’ ratio between number and mass is found for sites not affected by local emissions. This paper is the first part of two companion papers of which the second part describes chemical characteristics.
Keywords: Aerosol; Chemical composition; PM10; PM2.5; Compilation;

A European aerosol phenomenology—2: chemical characteristics of particulate matter at kerbside, urban, rural and background sites in Europe by Jean-P Putaud; Frank Raes; Rita Van Dingenen; Erika Brüggemann; M.-Cristina Facchini; Stefano Decesari; Sandro Fuzzi; Robert Gehrig; Cristoph Hüglin; Paolo Laj; Gundi Lorbeer; Willy Maenhaut; Nikolaos Mihalopoulos; Konrad Müller; Xavier Querol; Sergio Rodriguez; Jürgen Schneider; Gerald Spindler; Harry ten Brink; Kjetil Tørseth; Alfred Wiedensohler (2579-2595).
This paper synthesizes data on aerosol (or particulate matter, PM) chemical characteristics, which were obtained in European aerosol research activities at natural, rural, near-city, urban, and kerbside sites over the past decade. It includes only two (nearby) sites in the semi-arid Mediterranean area, and lacks data from Eastern Europe. PM chemical compositions are compared with the PM mass concentrations in PM10, PM2.5, and further size resolved PM fractions (chemical mass closure). Such data sets are more comprehensive than those currently provided by air quality monitoring networks (e.g. EMEP, EUROAIRNET). Data available from 24 sites in Europe were reviewed. They were processed and plotted to allow comparisons in spite of differences in the sampling and analytical techniques used in various studies. A number of conclusions are drawn among which are the following.Organic matter appears to be the major component of PM10 and PM2.5, except at natural and rural background sites, where sulphate contribution may be larger. Mineral dust shows up as a major component of PM10 at kerbside sites. Black carbon contributes 5–10% to PM2.5 and somewhat less to PM10 at all sites, including the natural background sites. Its contribution seems higher (15–20%) at some of the kerbside sites, but these data may be affected by analytical artefacts. On days when PM10 >50 μg m−3, nitrate concentrations can overtake organic matter concentrations in PM10 and PM2.5. High PM concentration episodes are often observed in cold periods, when the pollutant dispersion is least. Measurements indicate that the condensation in the particle phase of semi-volatile species like nitrate and (unspecified) organics is also favoured by cold temperatures. In particles with a diameter <150 nm (i.e., most atmospheric particles), organic matter and black carbon are by far the major components.More data are known to be available within the scientific community, which could enrich the present data set and strengthen the conclusions made above. Most of them are not made available yet. The investment in new approaches, which would bridge the technological gap between scientific measurements and regulatory monitoring networks, is strongly needed.
Keywords: Aerosol; Chemical composition; PM10; PM2.5; Compilation;

Outdoor smog chamber experiments were performed to investigate the effects of the preexisting diesel soot particles on secondary aerosol formation. Diesel exhaust (50–240 μg m−3 of diesel soot particles) was added to the outdoor chambers without or with α-pinene (0.14 ppmV). The increase of medium polarity and organic composition change of diesel soot particles were tracked by analyzing deuterated alkanes, which were dosed to the system. Changes due to photooxidation of diesel soot exhaust were accelerated when α-pinene was added. Major α-pinene oxidation products were also analyzed from gas and particle samples and they were mostly carbonyl compounds such as cis-pinonaldehyde, cis-pinonic acid, pinalic-4-acid and 10-hydroxy pinonaldehyde. The partitioning coefficients of the major carbonyl products were much higher in diesel soot particles than predicted by theory. The high particle concentration of carbonyl products on diesel soot particles could be explained by heterogeneous acid-catalyzed reactions.
Keywords: α-pinene; Diesel soot particle; Partitioning; SOA yield; Heterogeneous reaction;

In this paper, two new methods are developed for the determination of the average emission factors of fine and ultra-fine particles for different groups of vehicles on a busy road. The values of these emission factors for heavy-duty trucks and light-duty cars are calculated, discussed, and compared with the previous results obtained mainly in laboratory conditions.
Keywords: Ultra-fine particles; Average emission factor; Busy road; Light cars; Diesel trucks;