Atmospheric Environment (v.37, #35)

The results of an about 2-week monitoring campaign of benzene concentration in a deep street canyon in the city of Naples are reported. Passive samplers were located at different heights on the road level (3–14–27 m). The geometry of the canyon is: width W=5.8 m and height H=33 m (Aspect Ratio, AR=H/W=5.7). Monitoring was carried out in two 6-day campaigns: 10–16 December 2002 and 14–20 January 2003. Traffic levels in the same street were measured to obtain typical daily curves of average vehicle flow vs. time. Sampling time was fixed in 2 days and 6 days. Therefore, 2-day and 6-day average benzene concentrations were measured.The results show that benzene is present at high concentration level in the street canyon. Two-day average concentration up to 23.8 μg m−3 was detected. In all the samples the benzene concentration at 3 m on the road level was higher than the threshold limit value of 10 μg m−3. The vertical concentration profiles of benzene were fitted assuming a first-order exponential decay. Values of the decay coefficient vary in the range 8×10−2–1.6×10−1  m−1.
Keywords: Deep street canyon; Benzene; Passive samplers; Vertical pollutant gradients;

A hybrid receptor model, combining the features of chemical mass balance models and non-negative factor analysis, is presented both in theoretical terms and from a more practical viewpoint. A section describes the mathematical details, and another section presents an uncomplicated set of aerosol data from Northeast Greenland and a step-to-step demonstration of how the data was analysed using the model. Since 1992 the model has proven useful in several air pollution studies of very different character.
Keywords: Receptor models; Non-negative factor analysis; Chemical mass balance models; Source apportionment;

Seasonal effects on the physico-chemical characteristics of PM2.1 in Rome: a study by SEM and XPS by L. Paoletti; B. De Berardis; L. Arrizza; M. Passacantando; M. Inglessis; M. Mosca (4869-4879).
A large body of epidemiological research has shown a significant statistical correlation between acute health effects and the fine fraction of urban particulate (PM2.5). There is still a wide debate over which characteristics of PM are responsible for the adverse health effects. The aim of this study was to evaluate seasonal effects on the composition and physico-chemical characteristics of PM2.1 (particulate with aerodynamic diameter<2.1 μm) in an urban area of Rome. The role as a “carrier” of carbonaceous particles was thoroughly studied using scanning electron microscopy with an EDS X-ray attachment and photo-electron spectroscopy (XPS). Atmospheric aerosol was analysed by ion chromatography to evaluate the soluble ions collected by an annular denuder. X-ray microanalysis data were subjected to hierarchical cluster analysis to classify the particles into groups (clusters) of similar chemical composition.We identified four clusters of particles in the PM2.1: carbonaceous particles, soil erosion particles, sulphates and metals. EDX spectra showed the presence of a surface coating containing S or sometimes S, K, Na on a variable percentage of carbonaceous particles. XPS data showed C, O, N, Si, S to be the most abundant elements with only a trace presence of Ca, Na and Fe. XPS spectra in the region of S2p peak confirm that the sulphur compounds in the PM2.1 are constituted by SO4 2− anion. The trend of the abundances in weight of S and N obtained by XPS showed an evident peak in summer. A similar summer peak was seen in the abundances of carbonaceous particles with S-coating obtained by SEM/EDX.
Keywords: Fine particulate; Analytical microscopy; Photoelectron spectroscopy; Physico-chemical composition; Seasonal trend; Rome;

Atmospheric deposition maps for the Rocky Mountains by Leora Nanus; Donald H Campbell; George P Ingersoll; David W Clow; M Alisa Mast (4881-4892).
Variability in atmospheric deposition across the Rocky Mountains is influenced by elevation, slope, aspect, and precipitation amount and by regional and local sources of air pollution. To improve estimates of deposition in mountainous regions, maps of average annual atmospheric deposition loadings of nitrate, sulfate, and acidity were developed for the Rocky Mountains by using spatial statistics. A parameter-elevation regressions on independent slopes model (PRISM) was incorporated to account for variations in precipitation amount over mountainous regions. Chemical data were obtained from the National Atmospheric Deposition Program/National Trends Network and from annual snowpack surveys conducted by the US Geological Survey and National Park Service, in cooperation with other Federal, State and local agencies. Surface concentration maps were created by ordinary kriging in a geographic information system, using a local trend and mathematical model to estimate the spatial variance. Atmospheric-deposition maps were constructed at 1-km resolution by multiplying surface concentrations from the kriged grid and estimates of precipitation amount from the PRISM model. Maps indicate an increasing spatial trend in concentration and deposition of the modeled constituents, particularly nitrate and sulfate, from north to south throughout the Rocky Mountains and identify hot-spots of atmospheric deposition that result from combined local and regional sources of air pollution. Highest nitrate (2.5–3.0 kg/ha N) and sulfate (10.0–12.0 kg/ha SO4) deposition is found in northern Colorado.
Keywords: Atmospheric deposition; GIS; Kriging; Precipitation chemistry; Rocky Mountains;

PCDD/F emissions from burning wheat and rice field residue by Brian Gullett; Abderrahmane Touati (4893-4899).
This paper presents the first known values for emissions of polychlorinated dibenzodioxins and dibenzofurans (PCDDs/Fs) from combustion of agricultural field biomass. Wheat and rice straw stubble collected from two western US states were tested in a field burn simulation to determine emission factors. The resulting emission factor was approximately 0.5 ng toxic equivalency (TEQ)/kg burned for both sources. When coupled with published agricultural data on crop residue burning, about 1 g TEQ/year can be expected from wheat and rice straw residue burning, making this an apparently minor source of PCDDs/Fs in the United States.
Keywords: Agricultural field burning; Polychlorinated dibenzodioxin; Polychlorinated dibenzofuran; Emission factors; Wheat stubble; Rice stubble;

An updated estimation of the stable carbon and oxygen isotopic compositions of automobile CO emissions by Urumu Tsunogai; Yosuke Hachisu; Daisuke D. Komatsu; Fumiko Nakagawa; Toshitaka Gamo; Ken-ichi Akiyama (4901-4910).
We estimate up-to-date values of the average isotopic compositions of CO emitted from automobiles. In the estimation, we determined the isotopic compositions of CO in tail pipe exhaust for four gasoline automobiles and two diesel automobiles under varying conditions of both idling and running. While the dependence on the automobile manufacturer is little, each automobile equipped with functional catalytic converter exhibits a large temporal δ 13C and δ 18O variation. They tend to show 13C and 18O enrichment in accordance with the reduction of CO in exhaust, suggesting that the functional catalytic converter in engines enhances the δ 13C and δ 18O values of CO from tail pipes through a kinetic isotope effect during CO destruction. Assuming that automobiles run a modeled driving cycle, we estimated the average δ 13C and δ 18O of CO to be −23.8±0.8‰PDB and +25.3±1.0‰SMOW, respectively, for recent gasoline automobiles, and −19.5±0.7‰PDB and +15.1±1.0‰SMOW, respectively, for recent diesel automobiles. While the δ 13C and δ 18O values of recent gasoline automobiles coincide well with the isotopic compositions of source CO in present trunk road atmosphere estimated in this study, those are +4–+6‰ (δ 13C) and +1–+3‰ (δ 18O) higher than those reported previously and also those emitted from old, non-catalyst automobiles determined in this study. Recent improvements in functional catalytic converters have enhanced and will enhance the δ 13C and δ 18O values of CO from automobiles.
Keywords: Gasoline automobile; Carbon monoxide; Exhaust; Isotope; Functional catalytic converter; Kinetic isotope effect;

Surface ozone measurements at tropical rural coastal station Tranquebar, India by S.B. Debaje; S.Johnson Jeyakumar; K. Ganesan; D.B. Jadhav; P. Seetaramayya (4911-4916).
Surface ozone (O3) has been measured at Tranquebar (11°N, 79.9°E), a tropical rural coastal site on the east coast (the Bay of Bengal) of southeast India, during the period from May 1997 to October 2000. The measurements have shown that there exists a significant diurnal cycle/oscillation of average O3 with a maximum concentrations (33±4 ppbv) in the afternoon and average minimum O3 concentrations (11±2 ppbv) at sunrise with 1σ standard deviation. Further, O3 measurements have also shown that average higher concentrations (23±9 ppbv) in May and lower concentrations (17±7 ppbv) in October at this site. The reason for this high O3 in May (low O3 in October) is mainly due to active (inactive) photochemical production mechanism along with favourable (unfavourable) meteorological conditions and the related increasing (decreasing) precursors concentration. The increase in O3 is attributed to the increase in NO x and other O3 precursor emissions by different sources in the proximity of this site. The daytime and nighttime average O3 concentration are 30±3 and 13±2 ppbv with 1σ standard deviation.It is important to note here that, average O3 concentration (21±8 ppbv) in January at Tranquebar appears to be quite low as compared to the O3 concentration over the inland sites, whereas average O3 concentration (23±9 ppbv) in May is more or less in the same range.
Keywords: Surface ozone; Meteorological parameters; Coastal site; Ozone precursor; Tropospheric photochemistry;

This work presents an alternative technique in formulating an analytical form of the joint probability density function (pdf) of velocity for turbulent flows. The technique was rigorously developed by Koehler and Symanowski (J. Multivariate Anal. 55 (1995), 261–282), by which a joint pdf is constructed based on the prescribed or given knowledge of marginal distributions and strictly conserves the original shape of each marginal density. The technique also provides flexibility in estimating parameters required in the pdf to fit a specified correlation. The scope of work is limited to the formulation for two velocity components due to less difficulty in examining correlation structures. Illustrated and discussed are a number of pdfs, with emphasis on atmospheric turbulence where the vertical velocity is assumed to be positively skew and negatively correlated with the horizontal velocity.
Keywords: Probability density function; Velocity; Atmospheric Boundary Layer; Turbulence;

A pragmatic mass closure model for airborne particulate matter at urban background and roadside sites by Roy M. Harrison; Alan M. Jones; Royston G. Lawrence (4927-4933).
Twenty-four hour samples of airborne PM10 particulate matter have been collected as coarse and fine fractions using automated dichotomous samplers at four paired roadside and urban background locations in London and Birmingham, UK. The samples have been analysed for sulphate, nitrate, chloride, organic carbon, elemental carbon, iron and calcium and the data have been used to construct a simple model of aerosol chemistry. It is assumed initially that the major components are ammonium sulphate, ammonium nitrate, sodium chloride, elemental carbon, organic carbon and mineral dusts (for which iron and calcium are tracers).This leaves a small proportion of mass unaccounted for, which we attribute to strongly bound water. Increasing the ammonium sulphate and ammonium nitrate content by 29% allows 100% of mass to be accounted for with a high percentage of variance in 24 h mass concentrations explained.
Keywords: Particulate matter; PM10; PM2.5; Coarse fraction; Mass closure; Urban aerosol;

The decomposition of polycyclic aromatic hydrocarbons (PAHs) by ozone in gas and particles, under high-volume sampling, was studied by using in parallel a conventional device and a device protected with an oxidant denuder. Three different sampling regimes—short and long sampling under high-ozone concentration and long sampling under low-ozone concentration—were selected at three representative sampling sites—a boreal forest, an urban site and a background marine station. The results of our study suggest that most PAHs are susceptible to ozone degradation under high ozone atmospheric concentrations (>50 ppbv) and long sampling times (>24 h). The highest concentration ratio of total PAHs between the two sampling systems was observed under collection conditions of long sampling and high ozone concentration, especially for the gaseous PAHs (up to 2.10). Conversely, long sampling time under low ozone concentration did not affect the concentration of collected PAHs in the gas or particle phase. The most reactive PAHs collected on filters and polyurethane foam were cyclopentane[cd]pyrene and pyrene, respectively. The use of an oxidant denuder did not affect the PAH gas–particle distribution study. The slopes m r and the intercepts b r of the regression between the log  K p and log  P L 0 did not substantially deviate between the two sampling devices.
Keywords: Polycyclic aromatic hydrocarbons degradation; High-volume sampling; Sampling artifacts; Ozone denuder; Reactivity classification;

Size distribution of particle-bound polychlorinated dibenzo-p-dioxins and dibenzofurans in the ambient air of a municipal incinerator by Mu-Rong Chao; Chiung-Wen Hu; Hwong-Wen Ma; Gou-Ping Chang-Chien; Wen-Jhy Lee; Louis W. Chang; Kuen-Yuh Wu (4945-4954).
The atmospheric particle size distributions of 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) between 0.056 and 100 μm in aerodynamic diameter (D p) were measured at two sampling sites during January 2002. These sites were 1.1 and 2.1 km downwind from a municipal incinerator in central Taiwan, respectively. Size-segregated atmospheric particles were simultaneously collected by means of a cascade impactor and a rotary impactor. The results showed that PCDD/Fs were associated with the full size range of atmospheric particles. More than 80% of the ΣPCDD/Fs and toxic equivalents (TEQs) were found to be associated with fine particles of aerodynamic diameter, D p<2.0 μm. Generally a smaller particle had a higher ΣPCDD/Fs content. The particle size distributions of ΣPCDD/Fs and TEQs were shifted to larger particles with increasing time and distance. It is noteworthy that PCDFs were found to distribute significantly among aerosol size fractions based on their chlorination level at both sampling sites. There was an increase in the proportion of the less chlorinated PCDFs in the coarse particles (D p>2.0 μm). As for PCDDs, however, a relative enrichment of the less chlorinated congeners on coarse particles was found only at the farther sampling site (2.1 km).
Keywords: Incinerator; Particle size distribution; PCDD/Fs; Repartitioning;

Expressions were developed to relate the responses of the population to odor concentrations ranging from sub- to supra-threshold levels. Responses were expressed in terms of probability of detection, probability of discrimination and degree of annoyance. The proposed expressions each have two calibration parameters that are simply estimated and open to physical interpretation; i.e., a threshold parameter that reflects odor strength and a persistence parameter that reflects the variability of individuals within a population to register their responses to an odor over a range of concentrations. The ability of the expressions to accurately describe dose–response trends was confirmed by applying them to data collected for six pure chemical compounds in air. Dispersion modeling can be used in conjunction with the dose–response relationships to estimate contours of probability of response and degree of annoyance throughout the surrounding community which can serve as the basis for the development of odor impact parameters.
Keywords: Odors; Annoyance; Nuisance; Persistence; Threshold; Detection;

The effect of ethanol blended diesel fuels on emissions from a diesel engine by Bang-Quan He; Shi-Jin Shuai; Jian-Xin Wang; Hong He (4965-4971).
The addition of ethanol to diesel fuel simultaneously decreases cetane number, high heating value, aromatics fractions and kinematic viscosity of ethanol blended diesel fuels and changes distillation temperatures. An additive used to keep the blends homogenous and stable, and an ignition improver, which can enhance cetane number of the blends, have favorable effects on the physicochemical properties related to ignition and combustion of the blends with 10% and 30% ethanol by volume.The emission characteristics of five fuels were conducted on a diesel engine. At high loads, the blends reduce smoke significantly with a small penalty on CO, acetaldehyde and unburned ethanol 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. With the aid of additive and ignition improver, CO, unburned ethanol and acetaldehyde emissions of the blends can be decreased moderately, even total hydrocarbon emissions are less than those of diesel fuel. The results indicate the potential of diesel reformation for clean combustion in diesel engines.
Keywords: Diesel engine; Ethanol; Emission; Acetaldehyde; Additive; Ignition improver;

A comparison study of RAMS simulations with aircraft, wind profiler, lidar, tethered balloon and RASS data over Philadelphia during a 1999 summer episode by Anantharaman Chandrasekar; C Russell Philbrick; Bruce Doddridge; Richard Clark; Panos Georgopoulos (4973-4984).
This study presents comparisons of Colorado State University's prognostic mesoscale Regional Atmospheric Modeling System (RAMS 4.3) results with observational data obtained from aircraft, wind profiler, lidar, tethered balloon and RASS during the Northeast Oxidant and Particle Study (NE-OPS) field program at Philadelphia, PA during a summer episode in 1999. Model simulations were performed for the 15–20 July 1999 period. The comparison of model-predicted temperatures with aircraft and tethered balloon data revealed that the mean relative error exhibited the same general trend in time for temperature noted by earlier investigators. The comparisons of model relative humidity with aircraft and tethered balloon indicate that the mean relative error varied from −13% to −21%. The mean relative error for water vapor mixing ratio with respect to lidar data exhibited a negative bias consistent with humidity bias corresponding to aircraft and tethered balloon. The largest root mean square (rms) errors obtained from 36  km resolution RAMS results and the regular upper air rawinsonde stations are associated with the relative humidity values. The smallest rms errors for any variable are all associated with the lower atmosphere while the largest rms errors are associated with the upper/mid-tropospheric region. The difficulty in correctly predicting upper level humidity is due to lack of consistency in the upper level moisture observations while the lower rms errors of relative humidity close to surface are due to increased availability of moisture data at surface. The results of the present study, by utilizing a variety of diverse observational platforms, broadly confirm the general traits of RAMS performance noted by earlier investigators.
Keywords: RAMS; Aircraft; Lidar; Profiler; RASS; Tethered balloon;

Concentrations of n-alkanes, petroleum biomarkers such as hopanes and steranes, n-alkanoic acids, n-alkanols, polycyclic aromatic hydrocarbons (PAH), dicarboxylic acids, and selected oxygenated PAH were separately determined in total suspended particulate matter and associated vapour phase in ambient air in Birmingham, UK. Samples were taken simultaneously at two locations on 24 separate occasions every 1–2 weeks between August 1999 and August 2000. Site A was 10 m from a busy road, 800 m from site B that was located within the “green space” of the University of Birmingham campus. Despite some differences in concentrations of some compounds, data from this study is in line with that reported in London, UK and in California. Differences between Sites A and B in both concentrations and carbon preference indices are consistent with greater traffic inputs at Site A, with some evidence of an appreciable biogenic input of n-alkanols and n-alkanes at the less-traffic influenced and more vegetated Site B. The biogenic input at Site B appears greater in the spring and summer months and suggests that biogenic emissions are appreciable even in British urban areas. Secondary formation mechanisms for some compounds including dicarboxylic acids and oxygenated PAH like fluoren-9-one are indicated by the lack of any significant intersite difference in concentrations. Intersite differences in concentrations provide new evidence that while petroleum biomarkers arise predominantly from local traffic, regional as well as local sources play an important rôle for the higher molecular weight PAH which exist predominantly in the particle phase.
Keywords: Polycyclic aromatic hydrocarbons (PAH); n-alkanes; Petroleum biomarkers; Carbon preference indices (CPIs); Urban airborne particulate matter;