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Atmospheric Environment (v.45, #11)

Editorial board (pp. i).

Temporal trends and spatial patterns of heavy metal concentrations in mosses in Bulgaria and Switzerland: 1990–2005 by Lotti Thöni; Lilyana Yurukova; Ariel Bergamini; Ilia Ilyin; Daniela Matthaei (pp. 1899-1912).

Owing to their ability to accumulate heavy metals, mosses are especially suitable to monitor heavy metal airborne pollution. In Europe, starting in 1990 within the framework of UNECE ICP-Vegetation, the monitoring of background heavy metal deposition based on concentrations found in mosses were performed every five years in Switzerland, and, since 1995 also Bulgaria. Here we compare spatial and temporal trends of heavy metal depositions in these two countries and we assess to what extent a large scale European deposition model (MSCE-HM model) can be applied on these two countries.Highly significant differences in concentrations in mosses between the two countries were found for Cd, Cu, Ni, V, Cr, Fe, Pb. For Zn the differences were less clear, but still significant in 2000 and 2005. In Bulgaria, with the exception of Cr, heavy metal concentrations decreased between 1995 and 2005 (−14% to −29%). In Switzerland, Cd (−38%), Pb (−63%) and V (−23%) showed the strongest decrease between 1995 and 2005. For Fe, Ni and Zn no or only small concentration changes were found, whereas a considerable rise was recorded for Cr (+65%) and Cu (+15%). In comparison to median heavy metal concentrations in Europe, concentrations in Bulgaria were nearly always higher, while concentrations in Switzerland were always lower. For both Pb and Cd, relationships between modelled and moss-derived values for all of the years were highly significant, but explained variances were rather low. Overall, relationships between moss-derived depositions and modelled depositions were rather close to a 1:1-relationship in Switzerland. In Bulgaria the modelled depositions were considerably lower than the moss-derived depositions.Although deposition levels in Bulgaria also decreased, heavy metal concentrations in mosses were still high. In contrast to Switzerland, Bulgaria has a strong non-ferrous and ferrous heavy industry. New technologies must be implemented in order to reduce deposition levels in Bulgaria. Continuing the moss monitoring is crucial for future evaluations of environmental measures.► We compare the atmospheric accumulation of metals in mosses between Bulgaria (BG) and Switzerland (CH). ► Spatial and temporal trends between 1990 and 2005 were surveyed. ► Significantly higher concentrations were found in BG for Cd, Cu, Ni, V, Cr, Fe and Pb. ► In BG most metal concentrations decreased between 2000 and 2005, in CH between 1990 and 1995. ► EMEP-modelled Pb deposition fitted well to moss-derived in CH, but not in BG.

Keywords: Atmospheric deposition; EMEP modelling; Moss survey

Comparison of two thermal-optical methods for the determination of organic carbon and elemental carbon: Results from the southeastern United States by Yuan Cheng; Mei Zheng; Ke-bin He; Yingjun Chen; Bo Yan; Armistead G. Russell; Wenyan Shi; Zheng Jiao; Guoying Sheng; Jiamo Fu; Eric S. Edgerton (pp. 1913-1918).

A total of 333 PM_2.5 samples were collected at four sites in the southeastern Aerosol Research and Characterization Study (SEARCH) network during four seasons from 2003 to 2005 and were simultaneously analyzed by two common thermal-optical methods, the National Institute of Occupational Safety and Health (NIOSH) method and the Interagency Monitoring of Protected Visual Environments (IMPROVE) method. The concentrations of total carbon measured by the two methods were comparable, whereas the split of organic carbon (OC) and elemental carbon (EC) was significantly different. The NIOSH-defined EC was lower (up to 80%) than that defined by IMPROVE since the NIOSH method applied the transmittance charring correction and a much higher peak inert mode temperature. The discrepancy between NIOSH- and IMPROVE-defined EC showed distinct seasonal and spatial variations. Potential factors contributing to this discrepancy besides the analytical method were investigated. The discrepancy between NIOSH- and IMPROVE-defined EC was larger in the spring compared to winter due to the influence of biomass burning, which is known to emit significant amount of brown carbon that would complicate the split of OC and EC. The NIOSH-defined EC to IMPROVE-defined EC ratio reached its minimum (0.2–0.5) in the summer, when the largest discrepancy was observed. This was most likely to be attributed to the influence of secondary organic aerosol (SOA). Moreover, the discrepancy between NIOSH- and IMPROVE-defined EC was larger in the coastal and the rural sites where the presence of abundant SOA was found based on previous studies in this region, providing supporting evidence that SOA could contribute to the observed discrepancy in summer.► EC_NIOSH to EC_IMPROVE ratio shows distinct seasonal and spatial variations. ► Biomass burning might increase the discrepancy between EC_NIOSH and EC_IMPROVE. ► Secondary organic aerosol might also increase the discrepancy between EC_NIOSH and EC_IMPROVE.

Keywords: Carbonaceous aerosol; TOT; TOR; Brown carbon; Secondary organic aerosol

Sources of Cu, Zn, Cd and Pb in rainwater at a subtropical islet offshore northern Taiwan by Miao-Ching Cheng; Chen-Feng You; Fei-Jan Lin; Kuo-Fang Huang; Chuan-Hsiung Chung (pp. 1919-1928).

Pollutants derived from long-range transport and local emission impact significantly of heavy metal compositions in rainwater and aerosols. To identify their sources and relative contributions in rainwater, 47 monthly rainwater samples from January 1998 to December 2001, collected at Peng Chia Yu (PCY), a non-residential islet offshore Taiwan, were analyzed for heavy metals (i.e. Cu, Zn, Cd, and Pb) and Pb isotopic compositions.The dissolved metals concentrations of Al, Mn, Fe, Cu, Zn, Rb, Ba, and Pb in PCY rains are high in spring and winter, but low in summer. This can be understood in terms of pollutant source changes due to wind direction shifted seasonally. The average EF_crust and EF_seawater values calculated for Cu, Zn, Cd and Pb are far greater than 1500, suggesting their strong anthropogenic sources, also supported by the PCA results. The pollutants derived from long-range transport are the predominated heavy metals sources during the winter monsoon season, whereas local traffic emissions play the most important role during the summer monsoon period. Unique Pb isotopic fingerprints, similar to those of iron ore sinter dusts and oil combustion dusts from Shanghai and the traffic emissions from Taiwan were identified in PCY rainwater. A mixing model based on three typical end-member Pb isotopic compositions derived from Taiwan and China was applied to evaluate the pollutant sources variations.► The EF values show that metals in PCY rain originate from anthropogenic sources. ► The PCA results show that metals are derived from local traffic emissions in summer. ► Pollution sources from Asian countries impact Pb concentrations by model calculations.

Keywords: Heavy metals; Pb isotopes; Principal component analysis; Rainwater

Vehicle emissions in congestion: Comparison of work zone, rush hour and free-flow conditions by Kai Zhang; Stuart Batterman; François Dion (pp. 1929-1939).

Traffic congestion frequently occurs during rush hour periods and in work zones, and can account for a significant share of vehicle emissions and air quality impacts. This study estimates vehicle emissions from light- and heavy-duty vehicles (LDVs, HDVs) in work zone and rush hour congestion, which are compared to emissions under free-flow traffic conditions. Field experiments collected second-by-second vehicle speed and acceleration data on typical weekdays along a freeway segment that experienced both rush hour and work zone congestion. The collected data were smoothed and used in the Comprehensive Modal Emissions Model (CMEM) to generate second-by-second emissions. For LDVs and when expressed as g mi⁻¹ vehicle⁻¹, the highest emission rates of hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxide (NO_x) occurred during the transitional period when traffic changed from free-flow to congested conditions and vice-versa; the lowest rates occurred during low speed work zone congestion periods. However, the highest fuel consumption rates and the highest carbon dioxide (CO₂) emissions occurred under work zone congestion, while the lowest fuel consumption and CO₂ emissions occurred with rush hour congestion. On a link or emission density basis (e.g., g mi⁻¹ s⁻¹), rush hour congestion had the highest emission and fuel consumption rates. Results for HDVs differed in that work zone congestion was associated with the highest emissions of HC, CO and CO₂, and the highest fuel consumption, while NO_x emission rates under the different traffic conditions were similar. On an emission density basis, however, the rush hour congestion again was associated with the highest emissions of CO, NO_x and CO₂ (but not HC). The differences between congestion and free-flow conditions highlight the importance of accounting for congestion in emission, exposure and health risk evaluations, as well as transportation planning.► Emission rates depend on the type of congestion, e.g., work zone or rush hour. ► Microscopic models provide a way to estimate emissions in congestion. ► Congestion is generally associated with the highest emission intensity. ► Predictions of instantaneous emissions are sensitive to smoothing of speed data.

Keywords: Air quality; Comprehensive Modal Emissions Model; Congestion; Fuel consumption; Vehicle emissions; Work zone

Aerosol acidity and secondary organic aerosol formation during wintertime over urban environment in western India by R. Rengarajan; A.K. Sudheer; M.M. Sarin (pp. 1940-1945).

Atmospheric mass concentration of ambient PM_2.5, its chemical composition and aerosol acidity have been studied during the wintertime from an urban site in a semi-arid region of western India. The concentration of PM_2.5 ranged from 32 to 106 μg m⁻³ during the 30-day sampling period; and carbonaceous species (EC, OC) and water-soluble inorganic constituents (WSIC) account for ∼58% and ∼29% of the mass, respectively. The contribution of SO₄²⁻ to PM_2.5 is significant (Average: 17.5%) and that of NO₃⁻ is minor (Average: ∼2%). The ratio of water soluble to particulate organic carbon (WSOC/OC) varies from 0.26 to 0.52 (Average: 0.41) and provides evidence for the significant role of secondary organic aerosol (SOA) in an urban environment. Measured concentration of [H⁺]_air, used as an index of aerosol acidity, varies from 0.25 to 11 μmol m⁻³ and exhibits linear increase with the secondary organic carbon (SOC). Our field-based data provide the direct evidence for enhanced SOA formation at high level of acidity, consistent with laboratory studies.► In a semi-arid urban site from western India, PM_2.5 mass ranged from 32 to 106 μg m⁻³ during winter. ► (EC + OC) and water-soluble inorganic constituents (WSIC) account for ∼58% and ∼29%, respectively. ► Contribution of SO₄²⁻ is significant (Average: 17.5%) in WSIC and that of NO₃⁻ is minor (∼2%). ► Concentration of [H⁺]_aerosol, an index of aerosol acidity, exhibits linear increase with SOC.

Keywords: Urban aerosol; Elemental and organic carbon; Aerosol acidity; Secondary organic aerosol

A study of surface ozone variability over the Iberian Peninsula during the last fifty years by M.I. Fernández-Fernández; M.C. Gallego; J.A. García; F.J. Acero (pp. 1946-1959).

There is good evidence for an increase in the global surface level of ozone in the past century. In this work we present an analysis of 18 surface ozone series over the Iberian Peninsula, considering the target values of ozone for the protection of human health and for the protection of vegetation, as well as the information and alert thresholds established by the current European Directive on ambient air quality and cleaner air for Europe (Directive 2008/50/EC). The results show that the stations located on the Cantabrian coast exceeded neither the target value for the protection of human health nor the target value for the protection of vegetation. The information threshold was exceeded in most of the stations, while the alert threshold was only exceeded in one. The seasonal and daily evolution of ozone concentrations were as expected. A trend analysis of three surface ozone concentration indices (monthly median and 98th percentile, and monthly maximum of the daily maximum 8-h mean) was performed both for the whole period of each station and for the common period from 2001 to 2007 for all the months of the year. It was noted that generally the south of the Iberian Peninsula presented increasing trends for the three indices, especially in the last six months of the year, and the north decreasing trends. Finally, a correlation analysis was performed between the daily maximum 8-h mean and both daily mean temperature and daily mean solar radiation for the whole and the common periods. For all stations, there was a significant positive association at a 5% significance level between the daily maximum 8-h mean and the two meteorological variables of up to approximately 0.5. The spatial distribution of these association values from 2001 to 2007 showed a positive northwest to southeast gradient over the Iberian Peninsula.► Analysis of the Directive 2008/50/EC for surface ozone to EMEP series over the Iberian Peninsula (IP). ► Spatial distribution of surface ozone concentrations trends over the IP (2001–2007). ► Correlation between surface ozone concentrations and temperature and solar radiation.

Keywords: Tropospheric ozone; Ozone variability; Ozone trends; Iberian Peninsula

Applications of optical spectroscopy and stable isotope analyses to organic aerosol source discrimination in an urban area by N. Mladenov; L. Alados-Arboledas; F.J. Olmo; H. Lyamani; A. Delgado; A. Molina; I. Reche (pp. 1960-1969).

Understanding the chemical character of organic aerosols is extremely important for evaluating their role in climate forcing and human respiratory health. Aerosol columnar properties retrieved by sun photometry represent a large dataset of information about the physical and light absorbing and scattering properties of the total aerosol, but lack more detailed chemical information about the organic fraction of atmospheric particulate matter. To obtain additional information about relationships between organic aerosol sources and columnar properties, we simultaneously examined stable isotope properties of PM₁₀ aerosols from urban (Granada, Spain) and remote (Sierra Nevada, Spain) sites and diesel exhaust, spectroscopic properties of water soluble organic carbon (WSOC) of PM₁₀ aerosols, and sun photometry measurements. We demonstrated that C and N stable isotopes and parameters from UV–vis and fluorescence spectroscopy are able to discriminate between aerosols receiving substantial fossil fuel pollution and those influenced by Saharan dust in an urban area. More depleted δ¹³C was associated with low asymmetry parameter, g_λ, and high values of the spectral slope ratio, S_R, were associated with high effective radius, typical of pollution situations. The humification index (HIX), used predominantly to evaluate the degree of organic matter humification, was significantly related to g_λ and the radius of fine mode particles, r_f, and may reflect aging of the Saharan dust-influenced aerosols. Parallel factor analysis (PARAFAC) modeling identified a fluorescent component (C3) with a spectrum similar to that of naphthalene, which was significantly related to g_λ and r_f. The diesel exhaust sample represented a pollution end-member, with the lightest δ¹³C value (−26.4‰), lowest S_R (0.95), lowest HIX (2.77) and highest %C3 (20%) of all samples.► Optical spectroscopy, stable isotopes differentiate dust and urban organic aerosols. ► A fluorescent component was identified that may be used to track diesel pollution. ► Optical spectroscopy reflects aerosol aging and high molecular weight compounds. ► Optical spectroscopy characterization supports columnar aerosol physical properties.

Keywords: Fluorescence; Absorbance; PARAFAC; Diesel; Sun photometry; African dust

Sources and fluxes of Pt, Ir and REE in the Seoul metropolitan area through wet scavenging processes by Tseren-Ochir Soyol-Erdene; Yeongcheol Han; Borom Lee; Youngsook Huh (pp. 1970-1978).

Platinum group elements (PGEs: Pt and Ir) and rare earth elements (REEs) were analyzed in rainwater samples collected in Seoul during the summer of 2008 to identify their sources and quantify their wet-deposition fluxes to the Earth’s surface environment. Major (Na, K, Mg, Ca, NH₄⁺, SO₄²⁻, NO₃⁻, Cl⁻ and F⁻) and minor (Fe, Ba, Y and Hf) elements were also measured to facilitate interpretation. Evaluation of elemental correlations, crustal enrichment factors, Ir/Pt ratios and REE patterns indicated meteoric/volcanic sources for Pt and Ir and additional anthropogenic sources for Pt. REEs were predominantly of crustal origin. The relationship between concentrations and rainfall indicated that below-cloud scavenging (wash-out) was the main scavenging mechanism for most elements. The wet-deposition fluxes in Seoul were higher than those recorded in polar ice cores for Pt and Ir and were comparable to those from other rainwater studies of REEs in East Asia.► We identify the sources and quantify the wet-deposition fluxes of Pt, Ir and REE. ► Pt and Ir had meteoric/volcanic sources and additional anthropogenic sources for Pt. ► REEs were predominantly of crustal origin. ► Ir and REE were removed by below-cloud scavenging (wash-out). ► The wet-deposition fluxes in Seoul were higher than in polar ice cores for Pt and Ir.

Keywords: Rainwater; Platinum group elements; Wet-deposition flux; Enrichment factor

Ozone concentration forecast method based on genetic algorithm optimized back propagation neural networks and support vector machine data classification by Yu Feng; Wenfang Zhang; Dezhi Sun; Liqiu Zhang (pp. 1979-1985).

Multi Artificial Neural Network (ANN) models are used to forecast ozone concentration on single-site for a better forecast accuracy in huge dataset condition. Support Vector Machine (SVM) is used to accurately classify the data into its corresponding categories. Back Propagation neural network (BPNN) was optimized using Genetic Algorithm (GA) to achieve higher forecast stability. SVM classification and GA optimized BPNN (GABPNN) were combined to forecast ozone concentrations in Beijing. The ozone measurements of XiDan sampling site in Beijing were used to test the effectiveness of this method. The modeling dataset used were the records of temperature (T), humidity (H), wind velocity (WV) and UV radiation (UV) from Mar 2009 to Jul 2009. The models were tested using the records of Aug 2009. High accuracy was achieved using this forecast method. Correlation coefficient ( R) of the final models on the test stage ranged from 0.86 to 0.90, with an average of 0.87. The predictions of the final models represented a great forecasting capability that could be applied to the real-life ozone forecast in Beijing.► We introduced parallel computing theory to solve overfitting problem of Artificial Neural Networks in huge data condition in ozone prediction. ► We used model structure that the O₃ concentration at particular time point can be predicted after entering the predicted value of meteorological conditions obtained from weather report for that time point. ► We used GA to optimize BP Neural Network to increase forecast accuracy. ► We compared the outcome of BPNN, GABPNN and SVM-GABPNN, and concluded SVM-GABPNN is successful.

Keywords: Ozone forecast; Artificial neural networks; Genetic algorithm; Support vector machine; Meteorological conditions

Determining contributions of biomass burning and other sources to fine particle contemporary carbon in the western United States by Amanda S. Holden; Amy P. Sullivan; Leigh A. Munchak; Sonia M. Kreidenweis; Bret A. Schichtel; William C. Malm; Jeffrey L. Collett Jr. (pp. 1986-1993).

Six-day integrated fine particle samples were collected at urban and rural sampling sites using Hi-Volume samplers during winter and summer 2004–2005 as part of the IMPROVE (Interagency Monitoring of PROtected Visual Environments) Radiocarbon Study. Filter samples from six sites (Grand Canyon, Mount Rainier, Phoenix, Puget Sound, Rocky Mountain National Park, and Tonto National Monument) were analyzed for levoglucosan, a tracer for biomass combustion, and other species by High-Performance Anion-Exchange Chromatography with Pulsed Amperometric Detection (HPAEC-PAD). Contemporary carbon concentrations were available from previous carbon isotope measurements at Lawrence Livermore National Laboratory. Primary contributions of biomass burning to measured fine particle contemporary carbon were estimated for residential wood burning (winter) and wild/prescribed fires (summer). Calculated contributions ranged from below detection limit to more than 100% and were typically higher at rural sites and during winter. Mannitol, a sugar alcohol emitted by fungal spores, was analyzed and used to determine contributions of fungal spores to fine particle contemporary carbon. Contributions reached up to 13% in summer samples, with higher contributions at rural sites. Concentrations of methyltetrols, oxidation products of isoprene, were also measured by HPAEC-PAD. Secondary organic aerosol (SOA) from isoprene oxidation was estimated to contribute up to 22% of measured contemporary carbon. For each sampling site, a substantial portion of the contemporary carbon was unexplained by primary biomass combustion, fungal spores, or SOA from isoprene oxidation. This unexplained fraction likely contains contributions from other SOA sources, including oxidation products of primary smoke emissions and plant emissions other than isoprene, as well as other primary particle emissions from meat cooking, plant debris, other biological aerosol particles, bio-diesel combustion, and other sources. Loss of levoglucosan during atmospheric aging of biomass burning emissions likely also results in an underestimate of apportioned primary smoke contributions.► Biomass burning is an important source of particulate contemporary carbon. ► Levoglucosan degradation can bias biomass combustion estimates. ► Fungal spores contribute to summertime particulate contemporary carbon.

Keywords: Biomass burning; Source apportionment; Smoke; Levoglucosan; Methyltetrol; Mannitol

Impact of regulation on indoor volatile organic compounds in new unoccupied apartment in Korea by Soogil Lim; Kiyoung Lee; Sooyun Seo; Seongki Jang (pp. 1994-2000).

The Indoor Air Quality (IAQ) Control in Public Use Facilities Act in Korea, which came into effect on January 1, 2006, set standards of indoor environmental concentrations for benzene, toluene, ethylbenzene, xylenes, styrene, and formaldehyde. This study aimed to determine the impact of the Act on levels of volatile organic compounds (VOCs) and to identify factors associated with indoor VOCs levels. VOCs and formaldehyde levels were measured in 228 new, unoccupied apartments from 2005 to 2007. In 2005, the mean total VOC (TVOC) concentration in 108 unoccupied apartments was 1606 μg m⁻³. After 2006, mean TVOC concentration in 120 unoccupied apartments was 645 μg m⁻³, significantly lower than the 2005 level. In 2005, the percentages of apartments exceeding standards were 14% for xylenes, 5% for ethylbenzene, 3% for toluene, and 1% for formaldehyde. After 2006, no apartment exceeded standards. When other building characteristics were controlled, the concentrations of TVOC, toluene, ethylbenzene, xylenes, and formaldehyde after 2006 were significantly lower than 2005 levels. However, benzene and styrene levels did not change. The reduction in VOCs levels was significantly associated with flooring materials, adhesive, and paint. These findings demonstrate that regulation can reduce VOC concentrations in new apartments through the use of low-emission building materials.► IAQ regulation can reduce VOCs concentrations in new apartments. ► Concentrations of TVOC, VOCs and formaldehyde were reduced with implementation of regulation. ► IAQ is associated with use of low-emission building materials.

Keywords: Indoor air quality (IAQ); Regulation; VOCs; Formaldehyde; New apartments

Effect of fumigation methanol and ethanol on the gaseous and particulate emissions of a direct-injection diesel engine by Z.H. Zhang; K.S. Tsang; C.S. Cheung; T.L. Chan; C.D. Yao (pp. 2001-2008).

Experiments were conducted on a four-cylinder direct-injection diesel engine with methanol or ethanol injected into the air intake of each cylinder, to compare their effect on the engine performance, gaseous emissions and particulate emissions of the engine under five engine loads at the maximum torque speed of 1800 rev/min. The methanol or ethanol was injected to top up 10% and 20% of the engine loads under different engine operating conditions.The experimental results show that both fumigation methanol and fumigation ethanol decrease the brake thermal efficiency (BTE) at low engine load but improves it at high engine load; however the fumigation methanol has higher influence on the BTE. Compared with Euro V diesel fuel, fumigation methanol or ethanol could lead to reduction of both NOx and particulate mass and number emissions of the diesel engine, with fumigation methanol being more effective than fumigation ethanol in particulate reduction. The NOx and particulate reduction is more effective with increasing level of fumigation. However, in general, fumigation fuels increase the HC, CO and NO₂ emissions, with fumigation methanol leading to higher increase of these pollutants. Compared with ethanol, the fumigation methanol has stronger influence on the in-cylinder gas temperature, the air/fuel ratio, the combustion processes and hence the emissions of the engine.► Comparison emissions from a CI engine operating with fumigation methanol and ethanol. ► Investigation in the number concentration and size distribution of particles. ► Investigation in the variation of nano and ultrafine particles.

Keywords: Diesel engine; Methanol; Ethanol; Particulate emissions; Nano-particles

Setting maximum emission rates from ozone emitting consumer appliances in the United States and Canada by Glenn Morrison; Richard Shaughnessy; Shi Shu (pp. 2009-2016).

A Monte Carlo analysis of indoor ozone levels in four cities was applied to provide guidance to regulatory agencies on setting maximum ozone emission rates from consumer appliances. Measured distributions of air exchange rates, ozone decay rates and outdoor ozone levels at monitoring stations were combined with a steady-state indoor air quality model resulting in emission rate distributions (mg h⁻¹) as a function of % of building hours protected from exceeding a target maximum indoor concentration of 20 ppb. Whole-year, summer and winter results for Elizabeth, NJ, Houston, TX, Windsor, ON, and Los Angeles, CA exhibited strong regional differences, primarily due to differences in air exchange rates. Infiltration of ambient ozone at higher average air exchange rates significantly reduces allowable emission rates, even though air exchange also dilutes emissions from appliances. For Houston, TX and Windsor, ON, which have lower average residential air exchange rates, emission rates ranged from −1.1 to 2.3 mg h⁻¹ for scenarios that protect 80% or more of building hours from experiencing ozone concentrations greater than 20 ppb in summer. For Los Angeles, CA and Elizabeth, NJ, with higher air exchange rates, only negative emission rates were allowable to provide the same level of protection. For the 80th percentile residence, we estimate that an 8-h average limit concentration of 20 ppb would be exceeded, even in the absence of an indoor ozone source, 40 or more days per year in any of the cities analyzed. The negative emission rates emerging from the analysis suggest that only a zero-emission rate standard is prudent for Los Angeles, Elizabeth, NJ and other regions with higher summertime air exchange rates. For regions such as Houston with lower summertime air exchange rates, the higher emission rates would likely increase occupant exposure to the undesirable products of ozone reactions, thus reinforcing the need for zero-emission rate standard.► We propose maximum ozone emission rates from consumer appliances. ► We simulate indoor ozone in 4 cities based on building parameters and emission rates. ► Emission rates are <3 mg h⁻¹ and many are negative, suggesting zero-emission rate limits. ► Emission rate limits are driven by air exchange and outdoor ozone infiltration rates.

Keywords: Ozone; Monte Carlo analysis; Air cleaners; Regulation; Emission rates; Indoor air quality; Ventilation; Air exchange rate; Deposition velocity

Use of mixed ion exchange resin and the denitrifier method to determine isotopic values of nitrate in atmospheric deposition and canopy throughfall by P.H. Templer; K.C. Weathers (pp. 2017-2020).

The objective of this study was to test a technique that utilizes mixed bed resins and the denitrifier method to determine δ¹⁵N and δ¹⁸O of nitrate inputs under varying conditions found in the field. Temperature increases and greater loading of nitrogen led to significant increases in δ¹⁸O values and longer incubation times led to significant increases in δ¹⁵N values, but the changes were relatively small. Results of our study confirm that mixed ion exchange resin can be used to accurately measure natural abundance isotopic values of nitrate in samples of atmospheric deposition and throughfall. However, we also conclude that caution should be applied when using these mixed bed resins in the field if they will be exposed to high temperatures (e.g., >40 °C). This method can increase the feasibility of conducting high density sampling of stable isotopes in atmospheric deposition and canopy throughfall samples with the goal of identifying sources of nitrate, and thus represents an important methodological advance for ecosystem science.

Keywords: Ecological samples; Natural abundance; Stable isotopes; Partitioning sources of nitrate

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Atmospheric Environment (v.45, #11)