Atmospheric Environment (v.37, #16)

A multiple linear regression model incorporating meteorological parameters, annual cycles and random error due to serial correlation was used to investigate the annual and summer season ozone trends between 1985 and 2000 at five stations in the Greater Vancouver/Fraser Valley area of southern British Columbia. Results indicate that although average daily maximum ozone concentrations were relatively low compared to many urban areas of Canada, maximum levels, which typically occur during the summer, were similar to those measured in large urban centers in the Great Lakes-St. Lawrence corridor of southeastern Canada. Ozone levels were found to occasionally exceed the National Ambient Air Quality Objective of 82 ppb, although these occurrences were relatively infrequent. The annual cycle of ozone was typical of areas influenced by both background and locally produced ozone, as indicated by the spring peak followed by elevated maxima occurring during summer months. General Least Squares analysis performed on the meteorologically adjusted data found decreasing trends for summer ozone at all stations. Decreasing trends were also found for annual ozone for stations in the eastern portion of the study area, which are more strongly affected by locally produced ozone. These trends were consistent with local declines in ozone precursors and are in agreement with reported declines in summer ozone in urban areas of United States and Europe. In contrast, increasing trends were found for annual ozone at stations in the western portion of the study area, which, due to their geographical location, are less affected by locally produced ozone. There is some indication that increasing trends at sites in the western portion of the study area may be reflective of a hemispheric increase in background ozone levels. The results of this study suggest that ozone trends in the Greater Vancouver/Fraser Valley area are in line with broad changes in ozone occurring in North America and Europe.
Keywords: Ozone trends; Annual cycles; Spring maximum; General Least Squares;

Organic nitrogen deposition on land and coastal environments: a review of methods and data by S.E Cornell; T.D Jickells; J.N Cape; A.P Rowland; R.A Duce (2173-2191).
Despite over a century of published reports of dissolved organic nitrogen (DON) in precipitation, its implications are still being appraised. The number of studies focusing on atmospheric organic nitrogen deposition has increased steadily in recent years, but comparatively little has been done to draw together this disparate knowledge. This is partly a consequence of valid concerns about the comparability of analysis and sampling methodologies. Given the current global trends in anthropogenic nitrogen fixation, an improved qualitative and quantitative understanding of the organic nitrogen component is needed to complement the well-established knowledge base pertaining to nitrate and ammonium deposition. This global review confirms the quantitative importance of bulk DON in precipitation. This cumulative data set also helps to resolve some of the uncertainty that arises from the generally locally and temporally limited scale of the individual studies. Because of analytical and procedural changes in recent decades, assessments are made of the comparability of the data sets; caution is needed in comparisons of individual studies, but the overall trends in the compiled set are more robust. Despite the large number of reports considered, evidence for long-term temporal changes in rainwater organic nitrogen concentrations is ambiguous. With regard to sources, it is likely that some of the organic material observed is not locally generated, but undergoes extensive or long-range atmospheric transport. The compiled data set shows a land-to-sea gradient in organic nitrogen concentration. Possible precursors, reported data on the most likely component groups, and potential source mechanisms are also outlined.
Keywords: Dissolved organic nitrogen; Rainwater; Nitrogen cycling; Anthropogenic sources; Organic aerosol;

Atmospheric lifetime as a probe of radical chemistry in the boundary layer by Nadine Bell; Dwayne E. Heard; Michael J. Pilling; Alison S. Tomlin (2193-2205).
Determination of the atmospheric lifetime of radical species provides a potentially powerful method to resolve discrepancies between their modelled and measured concentrations. Theoretical perturbation analysis is employed to investigate the relationship between atmospheric lifetime (τ) and decay time (λ −1) following concentration perturbation for OH and HO2 using a model system with constrained NO x . It is shown that feedback from HO2 to OH can lead to a non-equivalence of (τ) and (λ −1), depending on the size of the feedback term and the difference in the atmospheric lifetimes of the coupled species. The ideas are applied and extended in a discussion of atmospheric field data from the EASE96 campaign at a remote coastal site. Dynamic information about the relaxation modes and species couplings, available from the eigenvector elements, is investigated for the systems studied. In general, the results suggest that the assignment of a specific decay time to OH is feasible for background boundary layer tropospheric conditions. However, complex couplings between peroxy species lead to non-separable time scales for these species. The relevance of results for the development of a field instrument to measure OH lifetime is discussed.
Keywords: Photochemistry; Hydrogen oxides; Chemical lifetimes; Perturbation analysis; Eigenmodes;

Processing of unsaturated organic acid films and aerosols by ozone by T.L. Eliason; S. Aloisio; D.J. Donaldson; D.J. Cziczo; V. Vaida (2207-2219).
For any organic-containing aerosol, the species present at the particle's surface are extremely susceptible to oxidation by atmospheric oxidants, such as OH, halogen atoms, ozone and nitrogen trioxide. In this work, thin films and pure organic aerosols were investigated as proxies for these surface organic compounds. The mechanisms of processing by ozone of unsaturated carboxylic acids, specifically 2-octenoic acid and 10-undecenoic acid, in a thin film are compared to that on pure aerosols. The organic acids utilized were chosen to investigate the effect of substitution on the ozonolysis mechanism. The gas-phase and condensed-phase products were probed via a combination of infrared spectroscopy and mass spectrometry. A significant change was measured in the chemical composition of both the thin films and the aerosols following ozonolysis, and some of the products formed have been identified. Consequences of this chemical processing of aerosols to atmospheric chemistry, climate and transport will be discussed.
Keywords: Ozone-alkene reaction; Mechanism; Atmospheric chemistry; Organic aerosol; Surface film;

In situ gas chromatographic measurements of halocarbons in an urban environment by Alison C Rivett; Damien Martin; Graham Nickless; Peter G Simmonds; Simon J O’Doherty; Daniel J Gray; Dudley E Shallcross (2221-2235).
A GC-ECD system has been used to make continuous measurements of nine halocarbons in the urban environment of Bristol, England over the course of about one month. A GC-FID system was deployed in the same location which simultaneously monitored over 30 C2–C8 hydrocarbons. In this paper, the halocarbon time series is presented and compared with the hydrocarbon data set. The influence of local sources is investigated by comparing the fluctuations in halocarbon concentrations with local weather conditions. A complex time series is seen, with no species displaying any clear diurnal cycle. Additionally, large deviations from baseline levels are observed for many of the compounds at different times. Local small-scale industry and landfill sites are postulated as the source of many of these excursions. The geography of Bristol has been found to influence levels of pollution in the city as the surrounding hills trap emissions and prevent their quick dispersion.
Keywords: Volatile organic compounds; Tropospheric air pollution; Landfill emissions; Industrial emissiona; Hydrocarbons;

In Gökova region where Yatağan is located there are three major uraniferous coal-fired power plants (CPPs) and they cause some pollution in the surroundings. Studies were realized over a wide area around the coal-fired power station located at Yatağan to evaluate the possible increase of natural radioactivity level due to the operation of the plant. The lichens Rhizoplaca melanophthalma, Cladonia convoluta, Cladonia pyxidata and the mosses Grimmia pulvinata, Hypnum cupressiforme were investigated for potential use as bioindicators for 210Po and 210Pb deposition. The maximum 210Po and 210Pb activities were observed around the hill close to ash stacks. The capture efficiency was the highest in one of the moss species, G. pulvinata with the activity concentration ranges of 600±19–1228±36 and 446±15–650±21 Bq kg−1 for 210Po and 210Pb, respectively. Soil samples were also collected and analysed in order to investigate any possible contamination in soil profiles due to CPPs and to determine unsupported 210Pb flux. The 210Pb and 226Ra concentrations in uncultivated soil profiles varied between 58±2 and 258±6 Bq kg−1, 50±5 and 58±5 Bq kg−1, respectively. The unsupported 210Pb inventory in the core was calculated to be 3312 Bq m−2. The corresponding annual 210Pb flux of 103 Bq m−2yr−1 is high with compare to estimates of the atmospheric flux given in literature for the same region.
Keywords: Natural radionuclides; Lichens; Mosses; Biomonitors;

Atmospheric fine particles (PM2.5) collected during August 1997–July 1998 and wintertime fog waters collected during 1997–1999 at Davis, California were analyzed for free and combined amino compounds. In both PM2.5 and fog waters, the average concentrations of combined amino compounds (CAC, e.g., proteins and peptides) were generally 4–5 times higher than those of free amino compounds (FAC, i.e., amino acids and alkyl amines). Concentrations of total amino compounds (TAC=FAC+CAC) ranged from 1260 to 3650 pmol m−3 air in PM2.5, and from 1620 to 5880 pmol m−3 air in fog waters. Average values (±1σ) were 2500±879 and 3400±1430 pmol m−3 air, respectively. Concentrations of amino compounds in PM2.5 varied seasonally, with a peak during late winter and early spring. Ornithine was a major FAC component in both PM2.5 and fog waters (typically accounting for ∼20% of FAC), but these sample types otherwise had fairly different FAC distributions. FAC in PM2.5 were enriched in protein-type amino species such as glycine/threonine, serine and alanine, while fog water FAC had significantly higher levels of non-protein species such as methylamine, γ-aminobutyric acid and ethanolamine. The compositions of CAC in PM2.5 and fogs were fairly similar and were mainly protein-type. Mass concentrations of TAC in PM2.5 and fog waters were, on average, 302 and 399 ng m−3 air, respectively. Amino compounds were an important component of the organic carbon pool for both fog and particles, with TAC accounting for an average of 13% of the dissolved organic carbon in fog waters and ∼10% of the water-soluble organic carbon in PM2.5. At these levels amino compounds likely play important roles in the chemistry of fog drops and fine particles, for example by influencing their buffering capacity and basicity.
Keywords: Organic nitrogen; Amino acids; Proteins; Buffering capacity; Organic carbon;

Pine needle samples were collected from Korea, Mexico, and the United States (total 9 sites) to compare the concentrations and sources of polycyclic aromatic hydrocarbons (PAHs). Total PAH concentrations ranged from 31 to 563 ng g−1 (wet wt.) and showed clear differences between rural (clean) and urban/industrialized (contaminated) sites. The lowest and highest concentrations were found in samples from a rural site in Korea and northern part of Mexico City, respectively. The PAH distribution patterns and the ratio of the sum of combustion specific PAHs (∑COMB) to total PAHs (∑PAHs) in samples from Korea and United States were similar, implying similar sources. At these sites, three-ring PAHs accounted for 63–73% of the total PAHs and phenanthrene was the predominant compound. Samples from Mexico City, however, had different PAH patterns and much higher ∑COMB/∑PAHs ratios (0.70 and 0.73). Four-ring PAHs were dominant (∼50%) and pyrene was the most abundant compound. Phenanthrene to anthracene and fluoranthene to pyrene ratios may provide an additional indication of different sources. The ratios of methylphenanthrene to phenanthrene suggest that the contribution of diesel-operated vehicles to the signature of PAHs is more significant in samples from Mexico City than other sites. Enriched high molecular weight PAHs and the ratios of some selected compounds found in Mexico City samples may be the results of more extensive combustion activities and a higher proportion of non-catalyst-equipped vehicles. This study confirms the usefulness of pine needles for source characterization as well as atmospheric organic contaminants monitoring on large spatial scales (e.g., national or global).
Keywords: Pine needles; PAHs; Sources; ∑ COMB ; Vehicle emission;

Measurements of hydrocarbon air–surface exchange rates over maize by M. Das; Daiwen Kang; V.P. Aneja; W. Lonneman; D.R. Cook; M.L. Wesely (2269-2277).
Vertical gradients of volatile organic compounds (VOCs) were measured over a maize (Zea mays) field, in its early growth period, during May 1995, in the Lower Coastal Plains of North Carolina. These measurements were combined with micrometeorological flux measurements to determine emission flux measurements for various VOCs. This measurement program was part of project NOVA (Natural emissions of Oxidant precursors: Validation of techniques and Assessment) to estimate the flux of VOCs. Average emissions of VOCs (and standard error) was estimated to be 4900±700 μg/m2/h out of which emission for methanol averaged (3450±420) μg/m2/h. A methanol emission rate of 35 μg/g/h was calculated for maize from the estimated emission of methanol and biomass density for the site.
Keywords: VOCs; Maize; Zea mays; Biogenic VOCs; VOC fluxes; Hydrocarbons; Air–surface exchange;

The reactions and corresponding system of equations for the inorganic SO4 2−–NO3 –NH4 + system have been studied with a new heterogeneous partitioning code, HETV. The code is based on the algorithms of ISORROPIA (Nenes et al., Aquat. Geochem. 4 (1998) 123; Atmos. Environ. 33 (1999) 1553), but was constructed for maximum computational efficiency on a vector supercomputer using the “vectorization by gridpoint” technique (Jacobson and Turco, Atmos. Environ. 28 (1994) 273). The new code was tested on two common computer architectures (vector supercomputers and UNIX workstations). The new code requires 1/38–1/89 of the processing time of the original ISORROPIA code on the vector supercomputer and produces equivalent results. A rigorous testing procedure was employed to compare the results of the two codes for conditions encompassing the typical range of SO4 2−, NO3 and NH4 + concentrations found in the ambient atmosphere. The procedure was instrumental in the creation of several improvements to the numerical methods for the solution of the system of equations. Both the improvements and the testing procedure are described in detail, and are recommended for future code development of this nature.
Keywords: Heterogeneous; Particle; Aerosol; Inorganic; Numerics;

Vehicle-generated fugitive dust transport: analytic models and field study by John M Veranth; Eric R Pardyjak; Gauri Seshadri (2295-2303).
Vehicle-generated road dust was measured under stable atmospheric conditions at a flat site in the Utah west desert, and the horizontal flux of the dust was calculated by integration of interpolation functions that are fit to the wind speed and dust concentration measurements at discrete heights. The site contained a uniformly spaced array of 2.5 m high×2.4 m×12.2 m roughness elements (cargo containers) simulating an urban setting. The dust measurement objective was to test the hypothesis that near-source removal of vehicle-generated dust may account for part of the reported systematic discrepancy between emission inventories based on AP-42 factors and receptor-based source apportionment studies. The horizontal flux of dust decreased to less than 15% of the initial value while traveling between measurement planes 3 and 95 m from the road, indicating significant near-source removal under the stable atmosphere and high surface roughness conditions of this field experiment. The magnitude of the flux was sensitive to assumptions about dust concentration and wind speed near the ground. The estimates for the flux at 3 m, obtained by integrating alternative interpolation functions, spanned the AP-42 value. Time-averaged data for meteorology, boundary layer turbulence, and dust concentration are provided to allow using the field observations for future theoretical analysis or numerical modeling studies.
Keywords: Vehicular pollution; Unpaved roads; Particulate matter; Emission factor; Deposition;