Atmospheric Environment (v.38, #26)

Experimental investigation of ozone accumulation overnight during a wintertime ozone episode in south Taiwan by Ching-Ho Lin; Yee-Lin Wu; Chin-Hsing Lai; Po-Hsiung Lin; Hsin-Chih Lai; Pay-Liam Lin (4267-4278).
From 12 to 15 December 2002, the area-averaged surface ozone concentrations in south Taiwan increased to 100 ppb from a background value of 40. The maximum hourly ozone concentration reached 150 ppb on 15 December. GPS-radiosondes, tethered ozonesondes and an instrumented ultralight aircraft were used to measure vertical ozone concentrations and meteorological conditions during this period. An ozone concentration of 60–90 ppb was observed in the nocturnal residual layer, 20–50 ppb of which was estimated to be produced from local photochemical reactions. Downward mixing of ozone from the residual layer to the ground level was observed in the morning of the episode day. Back air trajectory analysis was performed to locate the source region of the accumulated ozone. The results revealed that the source of high concentration of accumulated ozone was in an ozone-polluted area with an ozone concentration in the range 90–100 ppb on the previous day. About 60% of the ozone in the polluted area on the previous day persisted to the morning of the episode day.
Keywords: Ozone; Tethered ozonesonde; Ultralight; Residual layer; Taiwan;

Formation and evasion of dissolved gaseous mercury in large enclosures amended with 200HgCl2 by M Amyot; G Southworth; S.E Lindberg; H Hintelmann; J.D Lalonde; N Ogrinc; A.J Poulain; K.A Sandilands (4279-4289).
The mercury experiment to assess atmospheric loading in Canada and the United States (METAALICUS) aims at establishing the link between atmospheric deposition of mercury (Hg) and Hg concentrations in fish. As part of this initiative, we conducted an enclosure experiment in Lake 239 (ON, Canada). Our goal was to follow over time dissolved gaseous mercury (DGM) concentrations, after the addition of 200HgCl2, to assess post-depositional Hg dynamics. DGM concentrations reached very high levels in surface waters (up to 6 ng l−1) during the days following the spike. This increase in DGM levels coincided with a decrease in total Hg in the enclosure. Photoreduction rates of Hg were high after spiking (1 ng l−1  h−1) and decreased by two orders of magnitude during the summer, with low rates observed in August (0.01 ng l−1  h−1). These low rates may be caused by photobleaching of dissolved organic carbon. Water-to-air Hg fluxes (evasion) were measured with a flux chamber and modelled using DGM; both methods yielded similar fluxes when using time-averaged DGM values. Together, these results indicate that, under certain conditions, large amounts of newly deposited Hg(II) may be converted to DGM by photochemical processes and lost by evasion across the air/water interface.
Keywords: Enclosures; Mercury; Photoreduction; Evasion; METAALICUS;

Measurements of nitrous oxide emissions from light-duty motor vehicles: a pilot study by Eduardo Behrentz; Richard Ling; Paul Rieger; Arthur M. Winer (4291-4303).
Dynamometer testing in conjunction with high-resolution FTIR spectroscopy was used to measure exhaust emissions of nitrous oxide (N2O) from a fleet of 37 light-duty vehicles at the California Air Resources Board. Exhaust emissions were collected for two driving cycles: the Urban Dynamometer Driving Schedule and the Unified Cycle. The vehicles studied, including passenger cars, sport utility vehicles, and light-duty trucks, were a sub-sample of a fleet that represented California's in-use fleet. The highest correlation between the emissions of N2O and other vehicle-exhaust species was, as expected, between N2O and nitrogen oxides (r 2=0.45). The previously reported impact of catalyst aging on N2O emissions could not be verified by our data. Type of catalyst, driving cycle, and vehicle were demonstrated to be the main factors determining the magnitude of N2O emissions from gasoline-powered light-duty vehicles. The average N2O emissions factor for the 37 vehicles tested was 20±4 mg km−1, with a factor of 50 difference between the lowest (2 mg km−1) and highest (100 mg km−1) N2O emissions. The average value for N2O/NO x emissions ratios was 0.095±0.035, with a factor of 14 difference between the lowest (0.01) and the highest (0.14) ratios.
Keywords: Greenhouse gases; Dynamometer testing; Catalyst; FTIR spectroscopy; In-use fleet;

Chemical mass balance (CMB) analysis is a standard approach for apportioning observed pollutant concentrations to their various pollution sources. To use CMB analysis, the researcher must assume that all sources affecting the airshed are identifiable, and that the pollution source profile associated with each source can be speciated. We consider the performance of several solutions to the CMB equations for cases in which one or more solutions affecting the airshed are unknown. We demonstrate that the presence of unknown sources in the airshed can lead to substantial (and sometimes surprising) errors when estimating the known source contributions. A simple illustration of the effect of unknown sources on the problem is given and the vulnerability of iterative estimators (such as the effective variance estimator) in the presence of unknown sources is explained. Methods for detecting unknown sources are proposed and evaluated. We propose a test for detecting unknown sources that is based on an intercept term included in the CMB equations. The approaches considered are compared via computer simulation, and with an example using real PM2.5 data from the San Joaquin Valley Air Quality Study. We find that when unknown sources affect the airshed, a modified weighted least squares approach is superior to all other methods (including the effective variance approach).
Keywords: Receptor model; Chemical mass balance model; Unknown sources;

Moss bioconcentration of trace elements around a FeSi smelter: modelling and cellular distribution by J.A Fernández; J.R Aboal; J.A Couto; A Carballeira (4319-4329).
This article describes an evaluation of contamination by Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se and Zn in the surroundings of a FeSi smelter, by measurement of tissue levels of the elements in terrestrial mosses growing in the area. The total concentrations of As, Cu and Fe were modelled by surface response fitting. Use of the sequential elution technique (using EDTA as the extracellular displacing agent) enabled determination of the concentrations of Cu and Fe in the extra- and intracellular and insoluble particulate fractions. A gradient of exponentially decreasing contamination with increasing distance from the factory was found with all fractions except for the extracellular fraction of Zn. The advantages of using of the intracellular rather than the total fraction is discussed, i.e. the former clearly shows the dose–effect relationship and reveals the concentration-distance gradients as clearly as the latter, and the difficulties associated with toxicological risk evaluation are reduced (because of different bioavailabilities of the contaminants it is not possible to infer their concentrations from total fractions).
Keywords: Sequential elution; Bryophytes; Metals; Biomonitoring;

Size resolved traffic emission factors of submicrometer particles by Sara Janhäll; Åsa M. Jonsson; Peter Molnár; Erik A. Svensson; Mattias Hallquist (4331-4340).
Size resolved emission factors for submicrometer particles related to trace gases have been obtained from measurement data at a suburban road side, with a traffic intensity of 18,000 vehicles per day. Number of particles with diameter 10–368  nm , trace gases (NO, NO x ,O3 and SO2), traffic and meteorology parameters were measured outside of Göteborg, Sweden. Size distributions of small particles at the site are presented and their relation to meteorological and traffic related variables was evaluated. Wind speed correlated negatively with 10–368  nm particles and temperature correlated negatively with the smaller particles (10–60  nm ). Nitric oxide was shown to be a better tracer for traffic related ultrafine particles, than traffic intensity itself.The calculated emission factor, with errors at 95% confidence level, for particles in the range 10–368  nm is presented in relation to nitrogen oxides. The emission factors were 268±60 and 176±37  particles cm −3 per ppb NO and NO x , respectively. The particle emission factors for 10–100, 10–50, 50–170 and 170–368  nm were 260±70, 228±52, 41±11 and <1  particle cm −3 per ppb NO, respectively. The size distribution of the emissions is given by number of particles normalised by the width of the size bin, i.e. in units of dNd  log  Dp−1   ppb −1 . The maximum normalised emission factor was 450  cm −3 per ppb NO for 20  nm particles. The shape of the size distribution of emissions revealed one sharp peak at 20  nm , with a small shoulder at 70  nm .
Keywords: Ultrafine particles; Nitrogen oxides; Traffic; Emission factor; Urban atmosphere;

A large set of synchronous actinic flux and global irradiance data recorded in Thessaloniki (Greece) is used to determine the characteristics of the ratio of actinic flux to global irradiance as a function of global irradiance. The shape of this function is dominated by the values for clear and overcast sky conditions. Hence, model calculations carried out with the radiative transfer model UVSPEC for these two types of atmospheric conditions serve as boundary conditions. Then the ratio of actinic flux to global irradiance as a function of global irradiance is reproduced by an analytic function. This function depends on the boundary conditions and on one wavelength-dependent parameter. With the analytic function, the boundary conditions and the empirically determined parameter it is possible to convert any global irradiance data into actinic fluxes within reasonable uncertainties. This is demonstrated with data recorded in Thessaloniki (Greece), at the high mountain station Jungfraujoch (Switzerland), in Innsbruck (Austria) and in Weybourne (Great Britain). In the UVA and UVB for solar zenith angles up to about 60° the uncertainty in calculated actinic fluxes is 6% (twofold standard deviation, k=2) for the data taken from all four measurement sites. For larger solar zenith angles the uncertainties are on average 8% (k=2) in the UVB and about 12% (k=2) in the UVA. Afterwards photolysis rates for ozone and nitrogen dioxide derived from measured and calculated actinic fluxes are compared. The uncertainty in photolysis rates obtained from calculated actinic fluxes for ozone is about 7% (k=2) and for nitrogen dioxide about 12% (k=2).
Keywords: Photochemistry; Photolysis rates; Aerosol; Scattering; Climatology;

We investigated volatile nanoparticles emitted from two light-duty vehicles using a transmission electron microscope (TEM). Elemental analysis was performed with an energy dispersive system (EDS) attached to the microscope. Differences in stability of volatile nanoparticles during TEM analysis indicated two different chemical compounds. The results are consistent with the thesis that volatile nanoparticles are composed of a more volatile hydrophilic and a less volatile hydrophobic part. Sulfur and potassium were detected in volatile nanoparticles. These elements are likely to play an important role in the formation of volatile nanoparticles. Particle number size distributions derived from a scanning mobility particle sizer (SMPS) and from TEM image analysis were in good agreement.
Keywords: Nucleation; Microscopy; Exhaust; Traffic; Soot;

Spatio-temporal characterization of tropospheric ozone across the eastern United States by Jeff Lehman; Kristen Swinton; Steve Bortnick; Cody Hamilton; Ellen Baldridge; Brian Eder; Bill Cox (4357-4369).
This paper utilizes a rotated principal components approach first used by Eder, Davis, and Bloomfield (Atmos. Environ. 27a (16) (1993) 2645) to characterize non–urban daily 8-h maximum ozone (O3) concentrations within the eastern United States for the O3 seasons of 1993–2002. The analysis proceeds by selecting a spatially representative O3 database, imputing missing O3 concentrations using a spatial interpolation scheme, applying a rotated principal components analysis to delineate spatial regions of homogeneous concentrations, and investigating the temporal patterns exhibited by concentrations in each of the regions. Spatially, the analysis divides the eastern United States into five regions: a Northeast region, a Great Lakes Region, a Mid–Atlantic region, a Southwest region, and a Florida region. Concentrations are near the domain average for the Northeast, Great Lakes, and Southwest regions, are highest in the Mid–Atlantic region, and are lowest in the Florida region. Within each region the temporal patterns (e.g., seasonal trends, persistency, and annual trends) of O3 concentrations were quite different. The Northeast, Great Lakes, and Mid–Atlantic regions display a moderate amount of seasonal variability with peak concentrations occurring in late July, late June, and late July time periods, respectively. Conversely, the Southwest region exhibits a small amount of seasonal variability with peak concentrations occurring in late August, and the Florida region exhibits a relatively large amount of seasonal variability with peak concentrations occurring during the months of April and May. Ozone concentrations are most persistent in the Florida and Southwest regions (3–4 days of persistence), less persistent in the Mid–Atlantic region (2–3 days of persistence), and least persistent in the Northeast and Great Lakes regions (1 or 2 days persistence). These results demonstrate the spatial and temporal variability of O3 concentrations in the eastern United States and indicate that regional characterization (e.g., through aggregation of clusters of monitors) of O3 air quality may be a powerful yet simplifying air quality metric for determining seasonal trends, annual trends, and a variety of other O3 concentration characteristics.
Keywords: Principal component analysis; Influence regimes; Time series analysis; Persistence; Seasonality; Spatial modeling; 8-h ozone; Homogenous concentrations;

The term “accretion reactions” is introduced here to refer to the large collection of reactions by which atmospheric organic molecules can add mass, especially as by combination with other organic molecules. A general thermodynamic approach is developed for evaluating the tendency of atmospheric constituents (e.g., C10 aldehydes) to undergo accretion reactions (e.g., dimerization) and thereby form less volatile molecules (e.g., aldol condensation products) that may subsequently condense and so contribute to the levels of organic particulate matter (OPM) observed in the atmosphere. As an example, gaseous compounds A and B may contribute to OPM formation by the net overall reaction Ag+Bg=Cliq. This reaction may occur according to any of three kinetic schemes. Scheme I: (1) Ag+Bg=Cg (accretion in the gas phase): then (2) Cg=Cliq (condensation of the accretion product); Scheme II: (1) Bg=Bliq (condensation of B); then (2) Ag+Bliq=Cliq (heterogeneous accretion reaction of gaseous A with condensed B); or Scheme III: (1) Ag+Bg=Aliq+Bliq (condensation of A and B); then (2) Aliq+Bliq=Cliq (accretion of A with B within the PM phase). For all three schemes, the net overall reaction remains Ag+Bg=Cliq. The overall thermodynamic tendency of the net reaction remains the same regardless of the actual predominating kinetic mechanism.If an accretion reaction between two atmospheric components is to produce significant new OPM, appreciable amounts of the product C must form, and the vapor pressure of C must be relatively low so that a significant proportion of C can condense into the multicomponent liquid OPM phase. This study considers the thermodynamics of accretion reactions of atmospheric aldehydes including: (a) hydration, polymerization (i.e., oligomer formation), hemiacetal/acetal formation; and (b) aldol condensation. It was concluded regarding OPM formation that: (1) the reactions in the first group are not thermodynamically favored, either in the atmosphere, or in the “acid-catalyzed” chamber experiments of Jang and Kamens (Environ. Sci. Technol. 35 (2001b) 4758) with n-butanal, n-hexanal, n-octanal, and n-decanal; (2) aldol condensation is not thermodynamically favored for the conditions of the Jang and Kamens (2001b) experiments with those four aldehydes; (3) the mechanism for any observed OPM formation from n-butanal, n-hexanal, and n-octanal in those experiments remains unknown, and may also have been involved in the “acid-catalyzed” experiments with n-decanal; (4) whether Jang and Kamens (2001b) observed the consequences of aldol condensation in their n-decanal experiments remains unclear due in part to uncertainties in the free energy of formation (ΔG f 0) values for the aldol products of n-decanal; (5) analogous refinement in the quality of needed ΔG f 0 values is required to clarify the potential importance of aldol products of pinonaldehyde in the formation of ambient OPM; and (6) the possibility that photo-assisted mechanisms may compensate for unfavorable thermodyamics in the formation of accretion products in the atmosphere should be considered.
Keywords: Organic particulate matter; Particulate matter; Secondary organic aerosol; Organic aerosol formation; Accretion reactions; Acetal; Hemiacetal; Oligomers; Aldehydes; Aldol condensation;

Using an integrated assessment approach, we evaluate the impact that surface O3 in East Asia had on agricultural production in 1990 and is projected to have in 2020. We also examine the effect that emission controls and the enforcement of environmental standards could have in increasing grain production in China. We find that given projected increases in O3 concentrations in the region, East Asian countries are presently on the cusp of substantial reductions in grain production. Our conservative estimates, based on 7- and 12-h mean (M7 or M12) exposure indices, show that due to O3 concentrations in 1990 China, Japan and South Korea lost 1–9% of their yield of wheat, rice and corn and 23–27% of their yield of soybeans, with an associated value of 1990US$ 3.5, 1.2 and 0.24 billion, respectively. In 2020, assuming no change in agricultural production practices and again using M7 and M12 exposure indices, grain loss due to increased levels of O3 pollution is projected to increase to 2–16% for wheat, rice and corn and 28–35% for soybeans; the associated economic costs are expected to increase by 82%, 33%, and 67% in 2020 over 1990 for China, Japan and South Korea, respectively. For most crops, the yield losses in 1990 based on SUM06 or W126 exposure indices are lower than yield losses estimated using M7 or M12 exposure indices in China and Japan but higher in South Korea; in 2020, the yield losses based on SUM06 or W126 exposure indices are substantially higher for all crops in all three countries. This is primarily due to the nature of the cumulative indices which weight elevated values of O3 more heavily than lower values. Chinese compliance with its ambient O3 standard in 1990 would have had a limited effect in reducing the grain yield loss caused by O3 exposure, resulting in only US$ 0.2 billion of additional grain revenues, but in 2020 compliance could reduce the yield loss by one third and lead to an increase of US$ 2.6 (M7 or M12) –27 (SUM06) billion in grain revenues. We conclude that East Asian countries may have tremendous losses of crop yields in the near future due to projected increases in O3 concentrations. They likely could achieve substantial increases in future agricultural production through reduction of surface O3 concentrations and/or use of O3 resistant crop cultivars.
Keywords: Air pollution impacts; Ozone; Agriculture; East Asia; Integrated assessment;

By simultaneous sequential sampling of gas and rainwater from 1999 to 2000 in the campus of Kanagawa University in Yokohama, Japan, we investigated the wet-scavenging process of volatile organic compounds, some chlorinated hydrocarbons (CHs) and monocyclic aromatic hydrocarbons (MAHs), via rain droplets. Their volume-weighted mean concentrations in 125 rainwater were 4.98 nM for dichloromethane, 3.71 nM for toluene, 2.00 nM for benzene, 0.93 nM for 1,2-dichloroethane, 0.62 nM for o-xylene, 0.57 nM for m,p-xylene, 0.51 nM for p-dichlorobenzene, and 0.35 nM for trichloromethylene. Their rainwater concentrations did not depend on the rainfall intensity, and the temporal variation of their concentrations was similar to that of gas-phase concentrations. The dissolution of CHs and MAHs into rainwater, however, was larger than expected from their gas-phase concentrations at the ground and their temperature-corrected Henry's law constants. A simple below-cloud scavenging model, which was developed by Levine and Schwartz (Atmos. Environ. 16 (1982) 1725) could explain the independence of the rainfall intensity but not explain their enhanced dissolution in rainwater. The results of this study indicate the estimated concentrations, which were based on the Henry's law equilibrium, considerably underestimate the wet-deposition fluxes of CHs and MAHs onto the ground.
Keywords: Chlorinated hydrocarbons; Monocyclic aromatic hydrocarbons; Henry's law; Rainwater; The falling droplet approach;

Temporal/seasonal variations of size-dependent airborne fungi indoor/outdoor relationships for a wind-induced naturally ventilated airspace by Chung-Min Liao; Wen-Chang Luo; Szu-Chieh Chen; Jein-Wen Chen; Huang-Min Liang (4415-4419).
With the use of published temporal/seasonal size characteristics of fungal spores and meteorological data in the subtropical climate, we estimated the airborne fungal concentration indoor/outdoor (I/O) ratios in a wind-induced naturally ventilated home. We expanded previous size-dependent indoor air quality model based on a hygroscopic growth factor as a function of relative humidity (RH) on aerodynamic diameter and concentration of fungal spores. The average geometric mean diameters of airborne fungi decreased from outdoor 2.58±0.37 to indoor 1.91±0.12 μm in summer, whereas decreased from outdoor 2.79±0.32 to indoor 1.73±0.10 μm in winter, resulting from the effect of hygroscopicity of airborne fungi. The higher indoor airborne fungal concentrations occurred in early and late afternoon in which median values were 699.29 and 626.20 CFU m−3 in summer as well as 138.71 and 99.01 CFU m−3 in winter, respectively, at 2 a.m. and 8 p.m. In the absence of indoor sources, summer has higher mean I/O ratios of airborne fungal concentration (0.29 – 0.58) than that in winter (0.12 – 0.16). Parsimoniously, our proposed RH-corrected I/O ratio model could be used to estimate the indoor source concentrations of bioaerosols provided that the actual measured fungus-specific I/O ratios are available.
Keywords: Airborne fungus; Bioaerosol; Deposition; Hygroscopic; Humidity; Natural ventilation;