Concentration-dependent NH3 deposition processes for mixed moorland semi-natural vegetation

Dry deposition modelling typically assumes that canopy resistance (R_c) is independent of ammonia (NH₃) concentration. An innovative flux chamber system was used to provide accurate continuous measurements of NH₃ deposition to a moorland composed of a mixture of Calluna vulgaris (L.) Hull, Eriophorum vaginatum L. and Sphagnum spp. Ammonia was applied at a wide range of concentrations (1–100 μg m⁻³). The physical and environmental properties and the testing of the chamber are described, as well as results for the moorland vegetation using the ‘canopy resistance’ and ‘canopy compensation point’ interpretations of the data.Results for moorland plant species demonstrate that NH₃ concentration directly affects the rate of NH₃ deposition to the vegetation canopy, with R_c and cuticular resistance (R_w) increasing with increasing NH₃ concentrations. Differences in R_c were found between night and day: during the night R_c increases from 17 s m⁻¹ at 10 μg m⁻³ to 95 s m⁻¹ at 80 μg m⁻³, whereas during the day R_c increases from 17 s m⁻¹ at 10 μg m⁻³ to 48 s m⁻¹ at 80 μg m⁻³. The lower resistance during the day is caused by the stomata being open and available as a deposition route to the plant. R_w increased with increasing NH₃ concentrations and was not significantly different between day and night (at 80 μg m⁻³ NH₃ day R_w=88 s m⁻¹ and night R_w=95 s m⁻¹). The results demonstrate that assessments using fixed R_c will over-estimate NH₃ deposition at high concentrations (over ∼15 μg m⁻³).     

Surface ozone and NOx concentrations at a high altitude Mediterranean site,Greece

Ozone was measured in six- and NO_x in five sampling periods in 1996–97, mostly during summer, at a 1070 m altitude site in northern Peloponnese. Mean values in each sampling period ranged from 43–48 ppb exceeding the European Union 24 h plant protection standard. The background ozone concentration of 43 ppb derived from the correlation of ozone with NO^′_x also exceeded the EU plant protection standard. Ozone exhibited maxima in the afternoon and minima during the night; in certain 24–48 h periods, however, the ozone concentrations remained practically constant; in these short periods air mass back trajectories indicated air masses which originated in north Africa. NO^′_x concentrations had maximum of 24 h around noon. Their mean concentrations ranged from 0.5–0.7 ppb, smaller than respective concentrations in north-central Europe.     

Characteristics of puff dispersion in an urban environment

Instantaneous releases of sulfur hexafluoride tracer were carried out as part of the Joint Urban 2003 field campaign in Oklahoma City. Data from 10 fast-response tracer samplers were used to examine the crosswind and along-wind spread of the tracer, the decay of tracer concentrations, and the retention of tracer within approximately 1 km of the release locations. The time variation of the median values of the tracer concentrations, normalized by the peak value observed at a given sampler, could be approximately described by an exponential decay with characteristic decay times on the order of 1–2 min. The longer times were found for early morning releases and the shorter times were associated with later morning or afternoon releases, suggesting that atmospheric stability or the depth of the mixed layer may affect puff dispersion even in urban environments. The median retention times required for 99% of the exposure to be realized at a given location were found to be correlated reasonably well with the median decay times. These characteristic time scales should be regarded as lower limits for concentration decay because the analysis excluded a number of anomalous cases in which the decaying concentrations exhibited an extended tail that indicated a very slow ventilation rate. The median values of the along-wind dispersion parameter σ_x grouped into downwind distance ranges can be described by a linear variation with distance with an initial “hold up” contribution due to building effects of about 30–45 m, but there are considerable variations about this relationship. Downwind 0.5–1 km from the release point the lateral puff dispersion (σ_y) was roughly 70% of the along-wind dispersion.     

Long range transport of fine particle windblown soils and coal fired power station emissions into Hanoi between 2001 to 2008

Fine particulate matter (PM_2.5), source fingerprints and their contributions have been measured and reported previously at Hanoi, Vietnam, from 25 April 2001 to 31 December 2008. In this study back trajectories are used to identify long range transport into Hanoi for two of these sources, namely, windblown dust (Soil) from 12 major deserts in China and emissions from 33 coal fired power plants (Coal) in Vietnam and China. There were 28 days of extreme Soil events with concentrations greater than 6 μg m^?3 and 25 days of extreme Coal with concentrations greater than 30 μg m^?3 from a total of 748 sampling days during the study period. Through the use of back trajectories it was found that long range transport of soil from the Taklamakan and Gobi desert regions (more than 3000 km to the north west) accounted for 76% of the extreme events for Soil. The three local Vietnamese power stations contributed to 15% of the extreme Coal events, while four Chinese power stations between 300 km and 1700 km to the north-east of Hanoi contributed 50% of the total extreme Coal events measured at the Hanoi sampling site.     

Spatial patterns of mobile source particulate matter emissions-to-exposure relationships across the United States

Assessing the public health benefits from air pollution control measures is assisted by understanding the relationship between mobile source emissions and subsequent fine particulate matter (PM_2.5) exposure. Since this relationship varies by location, we characterized its magnitude and geographic distribution using the intake fraction (iF) concept. We considered emissions of primary PM_2.5 as well as particle precursors SO₂ and NO_x from each of 3080 counties in the US. We modeled the relationship between these emissions and total US population exposure to PM_2.5, making use of a source–receptor matrix developed for health risk assessment. For primary PM_2.5, we found a median iF of 1.2 per million, with a range of 0.12–25. Half of the total exposure was reached by a median distance of 150 km from the county where mobile source emissions originated, though this spatial extent varied across counties from within the county borders to 1800 km away. For secondary ammonium sulfate from SO₂ emissions, the median iF was 0.41 per million (range: 0.050–10), versus 0.068 per million for secondary ammonium nitrate from NO_x emissions (range: 0.00092–1.3). The median distance to half of the total exposure was greater for secondary PM_2.5 (450 km for sulfate, 390 km for nitrate). Regression analyses using exhaustive population predictors explained much of the variation in primary PM_2.5 iF (R²=0.83) as well as secondary sulfate and nitrate iF (R²=0.74 and 0.60), with greater near-source contribution for primary than for secondary PM_2.5. We conclude that long-range dispersion models with coarse geographic resolution are appropriate for risk assessments of secondary PM_2.5 or primary PM_2.5 emitted from mobile sources in rural areas, but that more resolved dispersion models are warranted for primary PM_2.5 in urban areas due to the substantial contribution of near-source populations.     

Concentration-dependent NH3 deposition processes for moorland plant species with and without stomata

Currently, in operational modelling of NH₃ deposition a fixed value of canopy resistance (R_c) is generally applied, irrespective of the plant species and NH₃ concentration. This study determined the effect of NH₃ concentration on deposition processes to individual moorland species. An innovative flux chamber system was used to provide accurate continuous measurements of NH₃ deposition to Deschampsia cespitosa (L.) Beauv., Calluna vulgaris (L.) Hull, Eriophorum vaginatum L., Cladonia spp., Sphagnum spp., and Pleurozium schreberi (Brid.) Mitt. Measurements were conducted across a wide range of NH₃ concentrations (1–140 μg m⁻³).NH₃ concentration directly affects the deposition processes to the vegetation canopy, with R_c, and cuticular resistance (R_w) increasing with increasing NH₃ concentration, for all the species and vegetation communities tested. For example, the R_c for C. vulgaris increased from 14 s m⁻¹ at 2 μg m⁻³ to 112 s m⁻¹ at 80 μg m⁻³. Diurnal variations in NH₃ uptake were observed for higher plants, due to stomatal uptake; however, no diurnal variations were shown for non-stomatal plants. R_c for C. vulgaris at 80 μg m⁻³ was 66 and 112 s m⁻¹ during day and night, respectively. Differences were found in NH₃ deposition between plant species and vegetation communities: Sphagnum had the lowest R_c (3 s m⁻¹ at 2 μg m⁻³ to 23 at 80 μg m⁻³), and D. cespitosa had the highest nighttime value (18 s m⁻¹ at 2 μg m⁻³ to 197 s m⁻¹ at 80 μg m⁻³).     

Statistical and diagnostic evaluation of a new-generation urban dispersion modelling system against an extensive dataset in the Helsinki area

We have developed a modelling system for predicting the traffic volumes, emissions from stationary and vehicular sources, and atmospheric dispersion of pollution in an urban area. This paper describes a comparison of the NO_x and NO₂ concentrations predicted using this modelling system with the results of an urban air quality monitoring network. We performed a statistical analysis to determine the agreement between predicted and measured hourly time series of concentrations at four permanently located and three mobile monitoring stations in the Helsinki Metropolitan Area in 1996–1997 (at a total of ten urban and suburban measurement locations). At the stations considered, the so-called index of agreement values of the predicted and measured time series of the NO₂ concentrations vary between 0.65 and 0.82, while the fractional bias values range from −0.29 to +0.26. In comparison with corresponding results presented in the literature, the agreement between the measured and predicted datasets is good, as indicated by these statistical parameters. The seasonal variations of the NO₂ concentrations were analysed in terms of the relevant meteorological parameters. We also analysed the difference between model predictions and measured data diagnostically, in terms of meteorological parameters, including wind speed and direction (the latter separately for two wind speed classes), atmospheric stability and ambient temperature, at two monitoring stations in central Helsinki. The modelling system tends to overpredict the measured NO₂ concentrations both at the highest (u⩾6 m s⁻¹) and at the lowest wind speeds (u<2 m s⁻¹). For higher wind speeds, the modelling system overpredicts the measured NO₂ concentrations in certain wind direction intervals; specific ranges were found for both monitoring stations considered. The modelling system tends to underpredict the measured concentrations in convective atmospheric conditions, and overpredict in stable conditions. The possible physico-chemical reasons for these differences are discussed.     

Regional dispersion of oxidized sulfur in Central Chile

Chile has a long tradition of exploiting mineral resources, particularly copper (Cu). One of the largest Cu smelters, Caletones, located some 150 km south of the country's capital, Santiago, in Central Chile, is responsible for about 0.4% of about 70 Tg S/yr oxidized sulfur (SO_x) emitted by anthropogenic sources worldwide. Santiago, a megacity with 5 million inhabitants, stands for about 5 Gg S/yr. The average meteorological conditions are unfavorable for the dispersion of pollutants in this area. All this poses risks for human health and vegetation. Also, downwind from these polluted areas there may be large-scale impacts on cloud properties and on oxidative cycles. Here, we present the first attempt to assess the regional distribution of SO_x in Central Chile using a dispersion model (MATCH) driven with data from a limited area weather forecast model (HIRLAM). Emphasis has been given to the impact of Cu smelters upon urban air quality, particularly that of Santiago. Six 1-month long periods were simulated for the years 1997, 1998 and 1999. These periods span over a broad range of typical meteorological conditions in the area including El Niño and La Niña years. Estimates of the regional dispersion and deposition patterns were calculated. The emissions from the large Cu smelters dominate the distribution of SO_x. A budget of SO_x over an area of 200×200 km² around Santiago is presented. There is too low a number of monitoring stations to perform a detailed evaluation of MATCH. Nevertheless, the model reproduces consistently all the regional-scale characteristics that can be derived from the available observations.     

Decadal reductions of traffic emissions on a transit route in Austria – results of the Tauerntunnel experiment 1997

Real-world emissions of a traffic fleet on a transit route in Austria were determined in the Tauerntunnel experiment in October 1997. The total number of vehicles and the average speed was nearly the same on both measuring days (465 vehicles 30 min⁻¹ and 76 km h⁻¹ on the workday, 477 and 78 km h⁻¹ on Sunday). The average workday fleet contained 17.6% heavy-duty vehicles (HDV) and the average Sunday fleet 2.8% HDV resulting in up to four times higher emission rates per vehicle per km on the workday than on Sunday for most of the regulated components (CO₂, CO, NO_x, SO₂, and particulate matter-PM10). Emission rates of NMVOC accounted for 200 mg vehicle⁻¹ km⁻¹ on both days. The relative contributions of light-duty vehicles (LDV) and HDV to the total emissions indicated that aldehydes, BTEX (benzene, toluene, ethylbenzene, xylenes), and alkanes are mainly produced by LDV, while HDV dominated emissions of CO, NO_x, SO₂, and PM10. Emissions of NO_x caused by HDV were 16,100 mg vehicle⁻¹ km⁻¹ (as NO₂). Produced by LDV they were much lower at 360 mg vehicle⁻¹ km⁻¹. Comparing the emission rates to the results that were obtained by the 1988 experiment at the same place significant changes in the emission levels of hydrocarbons and CO, which accounted 1997 to only 10% of the levels in 1988, were noticed. However, the decrease of PM has been modest leading to values of 80 and 60% of the levels in 1988 on the workday and on Sunday, respectively. Emission rates of NO_x determined on the workday in 1997 were 3130 mg vehicle⁻¹ km⁻¹ and even higher than in 1988 (2630 mg vehicle⁻¹ km⁻¹), presumable due to the increase of the HD-traffic.     

HNO3 analyzer by scrubber difference and the NO–ozone chemiluminescence method

A fast response analyzer for HNO₃ in highly polluted air is described. The time resolution attainable was 12 s. The method is based on the difference in a technique for HNO₃-scrubbed and non-scrubbed air and the reduction of HNO₃ to NO with the use of a line of catalytic converters and a method for the subsequent NO-ozone chemiluminescence. A sample air stream, in which particulates are removed with a Teflon filter, is divided into two channels. CH-1 is directly connected to the converter line, and CH-2 contains a HNO₃ scrubber packed with a nylon fiber that goes to another converter line. Each converter line is composed of a hot quartz-bead converter (QBC) and a molybdenum converter (MC) in a series. A QBC reduces HNO₃ to (NO+NO₂), which is called NO_x. The MC reduces the NO_x to NO.For CH-1, the analyzer detects most compounds that typically comprise NO_y (J. Geophys. Res. 91 (1986) 9781). These CH-1 compounds are called NO_y′ hereafter (NO_y-particulate nitrate) because the particulates are removed by the filter. A difference in the detector signal for the two channels indicates HNO₃. For a blank test, atmospheric air in which HNO₃ was pre-scrubbed by an extra nylon fiber was introduced to the analyzer. Variations in the blank value were 0.38±0.42 and 0.34±0.55 ppb during the high readings (NO_y′-HNO₃ ) (called NO_y^* hereafter) (111±12 ppb, N=180), and low NO_y^* readings (62±8 ppb, N=180), respectively, indicating that the lowest detection limit of the analyzer is 1.1 ppb (2σ). When the data obtained with the analyzer is compared to the data using the denuder method, a linear correlation with the regression of Y=0.973X+0.077 (r²=0.916 (N=20)) in the range of 0–6.5 ppb HNO₃ is obtained, which is an excellent agreement. Atmospheric monitoring was carried out at Kobe. Although the average concentration of HNO₃ was 2.6±1.3 ppb, ca.10 ppb for a HNO₃ concentration was occasionally observed when the NO_y^* concentration was high, i.e., more than 100 ppb.     

Hydrophobic organic compound partitioning from bulk water to the water/air interface

Partitioning of hydrophobic organic compounds to the interface between water and air may significantly affect the distribution and transfer of many xenobiotic chemicals between vapor and aqueous phases. The fluorescent probe, 1-methylperylene, was used to investigate the affinity of hydrophobic compounds for the water–air interface by varying the ratio of interfacial surface area to water volume in a fused-quartz cuvette. We found that the water–air/water interface partitioning coefficient [K_w−awi=1.2 mol cm^-2_awi/(mol ml^-1_w)] for this polycyclic aromatic hydrocarbon (PAH) was quantitatively consistent with partitioning to the same interface but from the airside, recently reported in the literature for less hydrophobic PAHs. Our results demonstrate significant partitioning from bulk water to the water/air interface for a hydrophobicity range relevant to many xenobiotic compounds. Anticipated implications of this process for the environmental chemistry of hydrophobic compounds include retarded gas-phase transport in unsaturated soils, bubble-mediated transport in water, droplet-mediated transport in the atmosphere, and photochemical reactions.     

PM10 measurements at McMurdo Station,Antarctica

PM₁₀ aerosols at McMurdo Station, Antarctica were sampled continuously during the austral summers of 1995–1996 and 1996–1997. PM₁₀ (particles with aerodynamic diameters less than 10 μm) mass concentrations at Hut Point, located less than 1 km from downtown McMurdo, averaged 3.4 μg m⁻³, more than an order of magnitude lower than the USEPA annual average National Ambient Air Quality Standard (NAAQS) of 50 μg m⁻³. Concentrations of methanesulfonate and nitrate were similar to those measured at other Antarctic coastal sites. Non-sea-salt sulfate (NSS) concentrations on Ross Island were higher than those found at other coastal locations. The average elemental carbon concentration (129 ng m⁻³) downwind of the station was two orders of magnitude higher than those measured at remote coastal and inland Antarctic sites during summer. Average sulfur dioxide concentrations (746 ng m⁻³) were 3–44 times higher than those reported for coastal Antarctica. Concentrations of Pb and Zn were 17 and 46 times higher than those reported for the South Pole. A methanesulfonate to biogenic sulfate ratio (R) of 0.47 was derived that is consistent with the proposed temperature dependence of R.     

Kinetics of the gas-phase reactions of NO3 radicals with ethyl acrylate,n-butyl acrylate,methyl methacrylate and ethyl methacrylate

The relative rate method has been used to determine the rate constants for the gas-phase reactions of NO₃ radicals with a series of acrylate esters: ethyl acrylate (k₁), n-butyl acrylate (k₂), methyl methacrylate (k₃) and ethyl methacrylate (k₄) at 298 ± 1 K and 760 Torr. The obtained rate constants are k₁ = (1.8 ± 0.25) × 10^?16 cm³ molecule^?1 s^?1, k₂ = (2.1 ± 0.33) × 10^?16 cm³ molecule^?1 s^?1, k₃ = (3.6 ± 1.2) × 10^?15 cm³ molecule^?1 s^?1, k₄ = (4.9 ± 1.7) × 10^?15 cm³ molecule^?1 s^?1. The experimental rate constants are in good agreement with theoretical rate constants calculated by an algorithm of the correlation between the rate constants and the orbital energies for the reactions of unsaturated VOCs with NO₃ radicals. In addition, the atmospheric lifetimes of the compound against NO₃ attack are estimated and the results show that NO₃ reactions contribute little to the atmospheric losses of acrylate esters except in polluted regions.     

The effect of humidity and state of water surfaces on deposition of aerosol particles onto a water surface

Deposition processes of particles with dry diameter larger than about 10 μm are dominated by gravitational settling, while molecular diffusion and Brownian motion predominate the deposition processes of particles smaller than 0.1 μm in dry diameter. Many air pollution derived elements exhibit characteristics common to sub-micron particles. The objective of the present study is to examine the effects of meteorological conditions within the turbulent transfer layer on the deposition velocity of particles with dry diameter between 0.1 and 1 μm. It is for these sub-micron particles that particle growth by condensation in the deposition layer, the broken water surface effect and the enhanced transfer process due to atmospheric turbulence in the turbulent transfer layer play important roles in controlling the particle deposition velocity. Results of the present study show that the `dry air’ assumption of Williams’ model is unrealistic. Effects of ambient air relative humidity and water surface temperature cannot be ignored in determining the deposition velocity over a water surface. Neglecting effects of ambient air relative humidity and water surface temperature will result in defining atmospheric stability incorrectly. It is found that the largest effect of air relative humidity on deposition velocity occurs at an air–water temperature difference corresponding to the point of `displaced neutral stability'. For a given wind speed of U=5 m s⁻¹ the additive effects of water surface temperature, T_w, changes from 5 to 25°C and ambient air relative humidity variations from 85 to 60%, respectively, lead to a maximum difference in v_d of about 20%. For a higher wind speed of 10 m s⁻¹, however, the corresponding change in v_d reduces to less than 5%. This is further confirmation that wind speed is one of the strongest variables that governs the magnitude of v_d. The present study also found that the broken surface transfer coefficient, k_bs, given as a multiple of the smooth surface transfer coefficient, k_ss, is physically more meaningful than assigning it a constant value independent of particle size. The method used in this study requires only a single level of atmospheric data coupled with the surface temperature measurement. The present method is applicable for determining deposition velocity not only at the conventional measurement height of 10 m but also at any other heights that are different from the measurement height.     

Effects of biodiesel on emissions of regulated air pollutants and polycyclic aromatic hydrocarbons under engine durability testing

An 80,000-km durability test was performed on two engines using diesel and biodiesel (methyl ester of waste cooking oil) as fuel in order to examine emissions resulting from the use of biodiesel. The test biodiesel (B20) was blended with 80% diesel and 20% methyl ester derived from waste cooking oil. Emissions of regulated air pollutants, including CO, HC, NO_x, particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) were measured at 20,000-km intervals. The identical-model engines were installed on a standard dynamometer equipped with a dilution tunnel used to measure the pollutants. To simulate real-world driving conditions, emission measurements were made in accordance with the United States Environmental Protection Agency (USEPA) FTP transient cycle guidelines. At 0 km of the durability test, HC, CO and PM emission levels were lower for the B20 engine than those for diesel. After running for 20,000 km and longer, they were higher. However, the deterioration coefficients for these regulated air pollutants were not statistically higher than 1.0, implying that the emission factors do not increase significantly after 80,000 km of driving. Total (gaseous+particulate phase) PAH emission levels for both B20 and diesel decreased as the driving mileage accumulated. However, for the engine using B20 fuel, particulate PAH emissions increased as engine mileage increased. The average total PAH emission factors were 1097 and 1437 μg bhp h⁻¹ for B20 and diesel, respectively. For B20, the benzo[a]pyrene equivalence emission factors were 0.77, 0.24, 0.20, 7.48, 5.43 and 14.1 μg bhp h⁻¹ for 2-, 3-, 4-, 5-, 6-ringed and total PAHs. Results show that B20 use can reduce both PAH emission and its corresponding carcinogenic potency.     

Laboratory studies on the uptake of aromatic hydrocarbons by ice crystals during vapor depositional crystal growth

Uptake of aromatic hydrocarbons (AH) by ice crystals during vapor deposit growth was investigated in a walk-in cold chamber at temperatures of 242, 251, and 260 K, respectively. Ice crystals were grown from ambient air in the presence of gaseous AH namely: benzene (C₆H₆), toluene (methylbenzene, C₇H₈), the C₈H₁₀ isomers ethylbenzene, o-, m-, p-xylene (dimethylbenzenes), the C₉H₁₂ isomers n-propylbenzene, 4-ethyltoluene, 1,3,5-trimethylbenzene (1,3,5-TMB), 1,2,4-trimethylbenzene (1,2,4-TMB), 1,2,3-trimethylbenzene (1,2,3-TMB), and the C₁₀H₁₄ compound tert.-butylbenzene. Gas-phase concentrations calculated at 295 K were 10.3–20.8 μg m⁻³. Uptake of AH was detected by analyzing vapor deposited ice with a very sensitive method composed of solid-phase micro-extraction (SPME), followed by gas chromatography/mass spectrometry (GC/MS).Ice crystal size was lower than 1 cm. At water vapor extents of 5.8, 6.0 and 8.1 g m⁻³, ice crystal shape changed with decreasing temperatures from a column at a temperature of 260 K, to a plate at 251 K, and to a dendrite at 242 K. Experimentally observed ice growth rates were between 3.3 and 13.3×10⁻³ g s⁻¹ m⁻² and decreased at lower temperatures and lower value of water vapor concentration. Predicted growth rates were mostly slightly higher.Benzene, toluene, ethylbenzene, and xylenes (BTEX) were not detected in ice above their detection limits (DLs) of 25 pg g_ice⁻¹ (toluene, ethylbenzene, xylenes) and 125 pg g_ice⁻¹ (benzene) over the entire temperature range. Median concentrations of n-propylbenzene, 4-ethyltoluene, 1,3,5-TMB, tert.-butylbenzene, 1,2,4-TMB, and 1,2,3-TMB were between 4 and 176 pg g_ice⁻¹ at gas concentrations of 10.3–10.7 μg m⁻³ calculated at 295 K. Uptake coefficients (K) defined as the product of concentration of AH in ice and density of ice related to the product of their concentration in the gas phase and ice mass varied between 0.40 and 10.23. K increased with decreasing temperatures. Values of Gibbs energy (ΔG) were between −4.5 and 2.4 kJ mol⁻¹ and decreased as temperatures were lowered. From the uptake experiments, the uptake enthalpy (ΔH) could be determined between −70.6 and −33.9 kJ mol⁻¹. The uptake entropy (ΔS) was between −281.3 and −126.8 J mol⁻¹ K⁻¹. Values of ΔH and ΔS were rather similar for 4-ethlytoluene, 1,3,5-TMB and tert.-butylbenzene, whereas 1,2,3-TMB showed much higher values.     

Ozone response to precursor controls: comparison of data analysis methods with the predictions of photochemical air quality simulation models

Comparisons were made between the predictions of six photochemical air quality simulation models (PAQSMs) and three indicators of ozone response to emission reductions: the ratios of O₃/NO_z and O₃/NO_y and the extent of reaction. The values of the two indicator ratios and the extent of reaction were computed from the model-predicted mixing ratios of ozone and oxidized nitrogen species and were compared to the changes in peak 1 and 8 h ozone mixing ratios predicted by the PAQSMs. The ozone changes were determined from the ozone levels predicted for base-case emission levels and for reduced emissions of volatile organic compounds (VOCs) and oxides of nitrogen (NO_x). For all simulations, the model-predicted responses of peak 1 and 8 h ozone mixing ratios to VOC or NO_x emission reductions were correlated with the base-case extent of reaction and ratios of O₃/NO_z and O₃/NO_y. Peak ozone values increased following NO_x control in 95% (median over all simulations) of the high-ozone (>80 ppbv hourly mixing ratio in the base-case) grid cells having mean afternoon O₃/NO_z ratios less than 5 : 1, O₃/NO_y less than 4 : 1, or extent less than 0.6. Peak ozone levels decreased in response to NO_x reductions in 95% (median over all simulations) of the grid cells having peak hourly ozone mixing ratios greater than 80 ppbv and where mean afternoon O₃/NO_z exceeded 10 : 1, O₃/NO_y was greater than 8 : 1, or extent exceeded 0.8. Ozone responses varied in grid cells where O₃/NO_z was between 5 : 1 and 10 : 1, O₃/NO_y was between 4 : 1 and 8 : 1, or extent was between 0.6 and 0.8. The responses in such grid cells were affected by ozone responses in upwind grid cells and by the changes in ozone levels along the upwind boundaries of the modeling domains.     

Surface ozone-temperature relationships in the eastern US: A monthly climatology for evaluating chemistry-climate models

We use long-term, coincident O₃ and temperature measurements at the regionally representative US Environmental Protection Agency Clean Air Status and Trends Network (CASTNet) over the eastern US from 1988 through 2009 to characterize the surface O₃ response to year-to-year fluctuations in weather, for the purpose of evaluating global chemistry-climate models. We first produce a monthly climatology for each site over all available years, defined as the slope of the best-fit line (m_O3-T) between monthly average values of maximum daily 8-hour average (MDA8) O₃ and monthly average values of daily maximum surface temperature (T_max). Applying two distinct statistical approaches to aggregate the site-specific measurements to the regional scale, we find that summer time m_O3-T is 3–6 ppb K^?1 (r = 0.5–0.8) over the Northeast, 3–4 ppb K^?1 (r = 0.5–0.9) over the Great Lakes, and 3–6 ppb K^?1 (r = 0.2–0.8) over the Mid-Atlantic. The Geophysical Fluid Dynamics Laboratory (GFDL) Atmospheric Model version 3 (AM3) global chemistry-climate model generally captures the seasonal variations in correlation coefficients and m_O3-T despite biases in both monthly mean summertime MDA8 O₃ (up to +10 to +30 ppb) and daily T_max (up to +5 K) over the eastern US. During summer, GFDL AM3 reproduces m_O3-T over the Northeast (m_O3-T = 2–6 ppb K^?1; r = 0.6–0.9), but underestimates m_O3-T by 4 ppb K^?1 over the Mid-Atlantic, in part due to excessively warm temperatures above which O₃ production saturates in the model. Combining T_max biases in GFDL AM3 with an observation-based m_O3-T estimate of 3 ppb K^?1implies that temperature biases could explain up to 5–15 ppb of the MDA8 O₃ bias in August and September though correcting for excessively cool temperatures would worsen the O₃ bias in June. We underscore the need for long-term, coincident measurements of air pollution and meteorological variables to develop process-level constraints for evaluating chemistry-climate models used to project air quality responses to climate change.     

Fungi and bacteria in mould-damaged and non-damaged office environments in a subarctic climate

The fungi and bacterial levels of the indoor air environments of 77 office buildings were measured in winter and a comparison was made between the buildings with microbe sources in their structures and those without such sources. Penicillium, yeasts, Cladosporium and non-sporing isolates were the commonest fungi detected in the indoor air and in settled dust, in both the mould-damaged and control buildings. Aspergillus ochraceus, Aspergillus glaucus and Stachybotrys chartarium were found only in environmental samples from the mould-damaged buildings. Some other fungi, with growth requiring of water activity, a_w, above 0.85, occurred in both the reference and mould-damaged buildings, but such fungi were commoner in the latter type of buildings. The airborne concentrations of Penicillium, Aspergillus versicolor and yeasts were the best indicators of mould damage in the buildings studied. Penicillium species and A. versicolor were also the most abundant fungi in the material samples. This study showed that the fungi concentrations were very low (2–45 cfu m⁻³ 90% of the concentrations being <15 cfu m⁻³) in the indoor air of the normal office buildings. Although the concentration range of airborne fungi was wider for the mould-damaged buildings (2–2470 cfu m⁻³), only about 20% of the samples exceeded 100 cfu m⁻³. The concentrations of airborne bacteria ranged from 12 to 540 cfu m⁻³ in the control buildings and from 14 to 1550 cfu m⁻³ in the mould-damaged buildings. A statistical analysis of the results indicated that bacteria levels are generally <600 cfu m⁻³ in office buildings in winter and fungi levels are <50 cfu m⁻³. These normal levels are applicable to subarctic climates for urban, modern office buildings when measurements are made using a six-stage impactor. These levels should not be used in evaluations of health risks, but elevated levels may indicate the presence of abnormal microbe sources in indoor air and a need for additional environmental investigations.