Typical Ambient Concentrations Research Articles

Wildfire plume ageing in the Photochemical Large Aerosol Chamber (PHOTO-LAC).

Plumes from wildfires are transported over large distances from remote to populated areas and threaten sensitive ecosystems. Dense wildfire plumes are processed by atmospheric oxidants and complex multiphase chemistry, differing from processes at typical ambient concentrations. For studying dense biomass burning plume chemistry in the laboratory, we establish a Photochemical Large Aerosol Chamber (PHOTO-LAC) being the world's largest aerosol chamber with a volume of 1800 m3 and provide its figures of merit. While the photolysis rate of NO2 (jNO2) is comparable to that of other chambers, the PHOTO-LAC and its associated low surface-to-volume ratio lead to exceptionally low losses of particles to the walls. Photochemical ageing of toluene under high-NOx conditions induces substantial formation of secondary organic aerosols (SOAs) and brown carbon (BrC). Several individual nitrophenolic compounds could be detected by high resolution mass spectrometry, demonstrating similar photochemistry to other environmental chambers. Biomass burning aerosols are generated from pine wood and debris under flaming and smouldering combustion conditions and subsequently aged under photochemical and dark ageing conditions, thus resembling day- and night-time atmospheric chemistry. In the unprecedented long ageing with alternating photochemical and dark ageing conditions, the temporal evolution of particulate matter and its chemical composition is shown by ultra-high resolution mass spectrometry. Due to the spacious cavity, the PHOTO-LAC may be used for applications requiring large amounts of particulate matter, such as comprehensive chemical aerosol characterisation or cell exposures under submersed conditions.

The impact of local fugitive particulate matter and emission inventories on air quality and health in dry and arid areas

The arid and semi-arid regions are facing a huge brunt of fugitive Particulate Matter (fPM) pollution, usually ascribed to the natural dust generated at the regional level (>100 km). In this study, the contribution of locally generated fPM to air pollution and it's environmental risk were assessed at a typical dry-arid area in the Middle East (i.e., State of Qatar, 200 × 200 km2 domain) with the use of different emission and dispersion models. Four modelling scenarios were constructed to reflect standard practices (e.g., regional emission models and the World Health Organization's (WHO) Environmental Burden of Disease (EBD) method) and higher resolution calculations with emission models that were developed in past field campaigns. Emphasis was given to the effect on the WHO methodology beyond the typical emission estimates and ambient concentration levels. Eventually, the use of higher spatial resolution population and concentration data revealed fPM hot spots yielding up to 11.0 times higher short-term excess mortalities (an average increase of 1.8 times) compared to the baseline WHO methodology, where the whole population was exposed to a single average concentration. A difference that could be attributed to the improvement of the emission estimations for barren lands and traffic. For example, the estimated PM10 emission fluxes from barren lands, within the main metropolitan area, using the improved emissions model ranged from 0.05 to 42.0 μg m−2 s−1, which is considerably higher than the emissions predicted using just the literature models (0.03 to 2.0 μg m−2 s−1). Overall, the barren lands emissions accounted for more than 90% of the fPM emissions during the study period. Consequently, this study is one of the first to quantify the significance of locally induced fPM and highlight the need for dedicated field studies and improved emissions estimation tools.

Particle number measurements within periodic technical inspections: A first quantitative assessment of the influence of size distributions and the fleet emission reduction

The enforcement of more stringent type approval emission standards de facto mandate manufacturers to equip vehicles with particle filters, which reduces the particle number concentration in automotive emissions to levels below typical ambient concentrations. Soon, the overall automotive particle emissions will be dominated by highly emitting vehicles with malfunctioned after-treatment systems, making tests of in-service compliance with emission standards inevitable. These tests are especially relevant for diesel-powered vehicles because broken diesel particle filters can increase the particle emissions by several orders of magnitude. For spark-ignition vehicles, the possible effect is significantly lower, and the implementation of corresponding tests is technically challenging. In this paper, particle number concentration measurements at idle speed for the identification of vehicles with malfunctioned particle filters have been studied. The results from a dedicated measurement campaign indicate that low cost equipment can be used for the identification of highly emitting diesel vehicles. The effectiveness of under-discussion instrument specifications has been evaluated employing simulations based on measured particle size distributions. Finally, an assessment of the potential impact of particle number measurements during periodic technical inspections on the fleet emission was performed. The corresponding results demonstrate that the enforcement of these measurements can reduce the overall particle emissions of the actual fleet by more than 80%.

Nitrogen-Dioxide Remains a Valid Air Quality Indicator.

In epidemiological studies, both spatial and temporal variations in nitrogen dioxide (NO2) are a robust predictor of health risks. Compared to particulate matter, the experimental evidence for harmful effects at typical ambient concentrations is less extensive and not as clear for NO2. In the wake of the “Diesel emission scandal—Dieselgate”, the scientific basis of current limit values for ambient NO2 concentrations was attacked by industry lobbyists. It was argued that associations between NO2 levels and medical endpoints were not causal, as NO2 in older studies served as a proxy for aggressive particulate matter from incineration processes. With the introduction of particle filters in diesel cars, NO2 would have lost its meaning as a health indicator. Austria has a high percentage of diesel-powered cars (56%). If, indeed, associations between NO2 concentrations and health risks in previous studies were only due to older engines without a particle filter, we should expect a reduction in effect estimates over time as an increasing number of diesel cars on the roads were outfitted with particle filters. In previous time series studies from Vienna over shorter time intervals, we have demonstrated distributed lag effects over days up to two weeks and previous day effects of NO2 on total mortality. In a simplified model, we now assess the effect estimates for moving 5-year periods from the beginning of NO2 monitoring in Vienna (1987) until the year 2018 of same and previous day NO2 on total daily mortality. Contrary to industry claims of a spurious, no longer valid indicator function of NO2, effect estimates remained fairly stable, indicating an increase in total mortality of previous day NO2 by 0.52% (95% CI: 0.35–0.7%) per 10 µg/m3 change in NO2 concentration.

Assessment of black carbon concentration as a potential measure of air quality at multi-purpose facilities

Despite its potential adverse health effects, black carbon (BC) has not received much attention from the perspective of managing indoor air quality at multi-purpose facilities. In this scenario, real-time measurements of indoor BC were performed in a classroom, in parking lots, and in airplane cabins. Results showed that the average typical indoor BC concentration in a classroom is approximately 1 μg/m³, which is comparable to a typical ambient BC concentration. The indoor and ambient BC concentrations were simultaneously measured using two microAeth AE51s. The indoor BC concentrations varied during the experiments depending on the ambient BC concentrations, suggesting that both indoor and ambient concentrations show site- and/or source-specific correlative responses. The highest BC concentration was observed in parking lots, and it instantaneously reached 39 μg/m3. Our approach has important advantages for certain tasks such as the identification of hotspots and the monitoring of variations in BC concentrations as a supplementary tool.

Measurement of isoprene nitrates by GCMS

Abstract. According to atmospheric chemistry models, isoprene nitrates play an important role in determining the ozone production efficiency of isoprene; however this is very poorly constrained through observations as isoprene nitrates have not been widely measured. Measurements have been severely restricted largely due to a limited ability to measure individual isoprene nitrate isomers. An instrument based on gas chromatography/mass spectrometry (GCMS) and the associated calibration methods are described for the speciated measurements of individual isoprene nitrate isomers. Five of the primary isoprene nitrates which formed in the presence of NOx by reaction of isoprene with the hydroxyl radical (OH) in the Master Chemical Mechanism are identified using known isomers on two column phases and are fully separated on the Rtx-200 column. Three primary isoprene nitrates from the reaction of isoprene with the nitrate radical (NO3) are identified after synthesis from the already identified analogous hydroxy nitrate. A Tenax adsorbent-based trapping system allows the analysis of the majority of the known hydroxy and carbonyl primary isoprene nitrates, although not the (1,2)-IN isomer, under field-like levels of humidity and showed no impact from typical ambient concentrations of NOx and ozone.

Night-Time Ground Hyperspectral Imaging for Urban-Scale Remote Sensing of Ambient PM—Modal Concentrations Retrieval

Retrieval of aerosol loading in vertical atmospheric columns is a common product of satellite and ground instruments that measure spectral extinction of solar radiation throughout the entire atmosphere. Here we study ground hyperspectral imaging of artificial light sources as a complementary method for retrieving fine aerosol concentrations along quazi-horizontal ambient open paths. Previously, we reported hyperspectral measurements of the aerosol optical thickness in the 500-900 nm range over urban-scale distances (180 m to 4 km), measuring the extinction of radiation emitted from a halogen source. Here we confirm in a laboratory-setup the basic premise that different accumulation-size aerosols generate distinct hyperspectral signatures in this spectral range. Measured hyperspectral attenuation signatures of fine aerosols were comparable to calculated Mie scattering signatures, suggesting that modal aerosol concentrations can be retrieved. A genetic algorithm was adapted to estimate the aerosol modal concentrations from its hyperspectral extinction signature. Retrievals of aerosol concentrations from measured and synthetic hyperspectral signatures indicated a robust algorithm, with an expected retrieval error of 0.2-22% for typical ambient concentrations along an urban-scale open path. The retrieval accuracy was found to depend on the relative aerosol modal concentrations, especially when there is a substantial overlap between the modal spectral signatures.

Distribution of Cryptosporidium oocysts and Giardia cysts in water above and below the normal limit of detection

Analysis of water samples for Cryptosporidium oocysts and Giardia cysts is a specialised and demanding pursuit. Understanding and evaluating data resulting from such analyses is equally specialised and complicated by the most common result--not finding any of the target organisms. Coming to an accurate conclusion regarding such monitoring results has been hampered by a lack of pertinent information presented in the context of current monitoring requirements. The work reported here presents laboratory data demonstrating an appropriate skewed distribution model statistical framework. It is shown that the Poisson model provides for understanding how Cryptosporidium oocysts and Giardia cysts are distributed in water at typical ambient concentrations that are near or most commonly below the limit of detection of the most widely used analytical procedure, USEPA Method 1623. From three to six replicate 50-L volumes of particle-free water were seeded with Cryptosporidium oocysts and Giardia cysts each at concentrations of ca. 0.2/L, 1-2/L, and 6-8/L. The seeded 50-L volumes were analysed in five 10-L aliquots to determine the number of oocysts and cysts in each. The data conformed to the Poisson distribution. This supports the interpretation that analysis of 10-L surface water samples resulting in not finding any target organisms is the result of their presence below the limit of detection. This interpretation strongly suggests that analysing fewer larger volume samples would provide more useful information.

Determination of Volatility Distributions of Primary Organic Aerosol Emissions from Internal Combustion Engines Using Thermal Desorption Gas Chromatography Mass Spectrometry

A new technique for measuring the primary organic aerosol (POA) emissions from internal combustion engines is presented. The method combines thermal-optical OC/EC analysis and thermal desorption gas chromatography mass spectrometry (TD-GC-MS) of quartz filter samples collected using a dilution sampler to quantify the total emissions of low-volatility organics and to distribute them across the volatility basis set. These data can be used in conjunction with partitioning theory to predict the gas-particle partitioning and thus the total amount of POA over the entire range of atmospheric conditions. The approach is evaluated using POA emissions data from two gas-turbine engines and one diesel generator. To evaluate the new method, we directly measured the effects of temperature and concentration on gas-particle partitioning of the emissions from each. Predictions based on the volatility distributions derived from the filter analyses are consistent with the direct partitioning measurements. The new approach represents a major improvement over the traditional assumption of nonvolatile POA emissions, which over predicts actual POA emissions from these sources by a factor of 2–4 at typical ambient concentration and temperature. By using quartz filter samples, this new technique is designed to be applied to routine source test data. Volatility distributions derived using this new approach can also be applied directly to the large catalog of quartz filter data used by existing emission inventories and models. The emissions data derived from this approach are designed for use in the next generation of chemical transport models and emissions inventories that employ the volatility basis set approach to explicitly track the gas-particle partitioning of POA emissions. Copyright 2012 American Association for Aerosol Research

Aerosol and trace gas vehicle emission factors measured in a tunnel using an Aerosol Mass Spectrometer and other on-line instrumentation

Abstract In this study we present measurements of gas and aerosol phase composition for a mixed vehicle fleet in the Gubrist tunnel (Switzerland) in June 2008. PM1 composition measurements were made with a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (AMS) and a Multi Angle Absorption Photometer (MAAP). Gas-phase measurements of CO, CO2, NOx and total hydrocarbons (THC) were performed with standard instrumentation. Weekdays had a characteristic diurnal pattern with 2 peaks in concentrations for all traffic related species corresponding to high vehicle density (∼300 ± 30 vehicles per 5 min) in the morning rush hour between 06:00 and 09:00 and in the afternoon rush hours from approximately 15:30 to 18:30. The emission factors (EF) of OA were heavily influenced by the OA mass loading. To exclude this partitioning effect, only organic aerosol mass concentrations from 60 μg m−3 to 90 μg m−3 were considered and for these conditions the EF(OA) value for HDV was 33.7 ± 2.3 mg km−1 for a temperature inside the tunnel of 20–25 °C. This value is not directly applicable to ambient conditions because it is derived from OA mass concentrations that are roughly a factor of 10 higher than typical ambient concentrations. An even higher EF(OA)HDV value of 47.4 ± 1.6 mg km−1 was obtained when the linear fit was applied to all data points including OA concentrations up to 120 μg m−3. Similar to the increasing EF, the OA/BC ratio in the tunnel was also affected by the organic loading and it increased by a factor of ∼3 over the OA range 10–120 μg m−3. This means that also the OA emission factors at ambient concentrations of around 5–10 μg m−3 would be 2–3 times lower than the emission factor given above. For OA concentrations lower than 40 μg m−3 the OA/BC mass ratio was below 1, while at an OA concentration of 100–120 μg m−3 the OA/BC ratio was ∼1.5. The AMS mass spectra (MS) acquired in the tunnel were highly correlated with the primary organic aerosol (POA) MS from a EURO 3 diesel vehicle with a speed similar to the average tunnel speed.

Theoretical versus Observed Gas-Particle Partitioning of Carbonyl Emissions from Motor Vehicles

A state-of-the-science thermodynamic model describing gas-particle absorption processes was used to predict the gas-particle partitioning of mixtures of approximately 60 carbonyl compounds emitted from low-emission gasoline-powered vehicles, three-way catalyst gasoline-powered vehicles, heavy-duty diesel vehicles under the idle-creep condition (HDDV idle), and heavy-duty diesel vehicles under the five-mode test (HDDV 5-mode). Exhaust was diluted by a factor of 120–580 with a residence time of approximately 43 sec. The predicted equilibrium absorption partitioning coefficients differed from the measured partitioning coefficients by several orders of magnitude. Time scales to reach equilibrium in the dilution sampling system were close to the actual residence time during the HDDV 5-mode test and much longer than the actual residence time during the other vehicle tests. It appears that insufficient residence time in the sampling system cannot uniformly explain the failure of the absorption mechanism to explain the measured partitioning. Other gas-particle partitioning mechanisms (e.g., heterogeneous reactions, capillary adsorption) beyond the simple absorption theory are needed to explain the discrepancy between calculated carbonyl partitioning coefficients and observed partitioning. Both of these alternative partitioning mechanisms imply great challenges for the measurement and modeling of semi-volatile primary organic aerosol (POA) species from motor vehicles. Furthermore, as emitted particle concentrations from newer vehicles approach atmospheric background levels, dilution sampling systems must fundamentally change their approach so that they use realistic particle concentrations in the dilution air to approximately represent real-world conditions. Samples collected with particle-free dilution air yielding total particulate matter concentrations below typical ambient concentrations will not provide a realistic picture of partitioning for semi-volatile compounds.

Uptake of Aldehydes and Ketones at Typical Indoor Concentrations by Houseplants

The uptake rates of low-molecular weight aldehydes and ketones by peace lily (Spathiphyllum clevelandii) and golden pothos (Epipremnum aureum) leaves at typical indoor ambient concentrations (10(1)-10(2) ppbv) were determined. The C3-C6 aldehydes and C4-C6 ketones were taken up by the plant leaves, but the C3 ketone acetone was not. The uptake rate normalized to the ambient concentration C(a) ranged from 7 to 19 mmol m(-2) s(-1) and from 2 to 7 mmol m(-2) s(-1) for the aldehydes and ketones, respectively. Longer-term fumigation results revealed that the total uptake amounts were 30-100 times as much as the amounts dissolved in the leaf, suggesting that volatile organic carbons are metabolized in the leaf and/or translocated through the petiole. The ratio of the intercellular concentration to the external (ambient) concentration (C(i)/C(a)) was significantly lower for most aldehydes than for most ketones. In particular, a linear unsaturated aldehyde, crotonaldehyde, had a C(i)/C(a) ratio of approximately 0, probably because of its highest solubility in water.

Relative kinetic measurements of rate coefficients for the gas-phase reactions of Cl atoms and OH radicals with a series of methyl alkyl esters

Abstract Relative kinetic studies have been performed on the reactions of Cl atoms with a series of methyl alkyl esters in a 405-liter borosilicate glass chamber at (298 ± 3) K and one atmosphere of synthetic air using in situ FTIR spectroscopy to monitor the reactants. Rate coefficients (in units of cm3 molecule−1 s−1) were determined for the following compounds: methyl acetate (2.48 ± 0.58) × 10−12; methyl propanoate (1.68 ± 0.36) × 10−11; methyl butanoate (4.77 ± 0.87) × 10−11; methyl pentanoate (7.84 ± 1.15) × 10−11; methyl hexanoate (1.09 ± 0.31) × 10−10; methyl heptanoate (1.56 ± 0.37) × 10−10; methyl cyclohexane carboxylate (3.32 ± 0.76) × 10−10; methyl-2-methyl butanoate (9.41 ± 1.39) × 10−11. In addition rate coefficients (in units of 10−11 cm3 molecule−1 s−1) have been obtained for the reactions of OH radicals with the following compounds: methyl butanoate (3.55 ± 0.71), methyl pentanoate (5.41 ± 1.08), and methyl-2-methyl butanoate (4.08 ± 0.82). Using the kinetic rate data tropospheric lifetimes for the methyl alkyl esters with respect to their reactions with OH, and Cl have been estimated for typical ambient air concentrations of these oxidants.

Charge-based personal aerosol samplers

There are several good reasons to use personal monitors for exposure control and health effect studies. But current personal monitoring methods are either not sensitive enough to measure typical ambient concentrations, work offline (masking short exposures to high concentrations), and/or require trained personnel to analyze the data, which makes them difficult to use. For this reason, we propose the use of a diffusion charging sensor as an online personal monitoring method, and present a miniaturized device (45 × 80 × 200 mm, 770 g) that works on this principle. Our device has a high time resolution and covers typically encountered ambient concentration ranges. It can measure very low particle concentrations of a few hundred particles per cubic centimeter even for ultrafine particles (i.e., two to three orders of magnitude more sensitive than rival technologies), while the upper detection limit is 1 million particles/cm3, which hardly ever occurs in ambient settings. While other methods measure a fixed quantity, the response of our device can be tuned to be proportional to the particle diameter to the power of x, with at least 0.3 ≤ x ≤ 1.35. This opens up the possibility of giving more weight to smaller particles, which is a key feature, since on a per-mass basis, smaller solid particles have been shown to be more toxic than larger ones.

An Automated Analyzer to Measure Surface-Atmosphere Exchange Fluxes of Water Soluble Inorganic Aerosol Compounds and Reactive Trace Gases

Here, we present a new automated instrument for semicontinuous gradient measurements of water-soluble reactive trace gas species (NH3, HNO3, HONO, HCl, and SO2) and their related aerosol compounds (NH4+, NO3-, Cl-, SO4(2-)). Gas and aerosol samples are collected simultaneously at two heights using rotating wet-annular denuders and steam-jet aerosol collectors, respectively. Online (real-time) analysis using ion chromatography (IC) for anions and flow injection analysis (FIA) for NH4+ and NH3 provide a half-hourly averaged gas and aerosol gradients within each hour. Through the use of syringe pumps, IC preconcentration columns, and high-quality purified water, the system achieves detection limits (3sigma-definition) under field conditions of typically: 136/207,135/114, 29/ 22,119/92, and 189/159 ng m(-3) for NH3/NH4+, HNO3/NO3-, HONO/ NO2-, HCl/Cl- and SO2/SO4(2-), respectively. The instrument demonstrates very good linearity and accuracy for liquid and selected gas phase calibrations over typical ambient concentration ranges. As shown by examples from field experiments, the instrument provides sufficient precision (3-9%), even at low ambient concentrations, to resolve vertical gradients and calculate surface-atmosphere exchange fluxes undertypical meteorological conditions of the atmospheric surface layer using the aerodynamic gradient technique.

Rate Coefficients for the Gas-Phase Reactions of OH and NO3Radicals and O3with Ethyleneglycol Monovinyl Ether, Ethyleneglycol Divinyl Ether, and Diethyleneglycol Divinyl Ether

Kinetic studies have been performed on the reactions of OH and NO(3) radicals and ozone with three ethyleneglycol vinyl ethers (EGVEs), that is, ethyleneglycol monovinyl ether (EGMVE, HOCH(2)CH(2)OCH=CH(2)), ethyleneglycol divinyl ether (EGDVE, H(2)C=CHOCH(2)CH(2)OCH=CH(2)), and diethyleneglycol divinyl ether (DEGDVE, H(2)C=CHOCH(2)CH(2)OCH(2)CH(2)OCH=CH(2)). Using a relative rate technique, rate coefficients have been determined for the reactions in a 405 L borosilicate glass chamber at (298 +/- 3) K in one atmosphere of synthetic air using in situ FTIR spectroscopy to monitor the reactants. The following rate coefficients (in units of cm(3) molecule(-1) s(-1)) were obtained: (1.04 +/- 0.22) x 10(-10), (1.23 +/- 0.33) x 10(-10), and (1.42 +/- 0.30) x 10(-10) for the reaction of OH with EGMVE, EGDVE, and DEGDVE, respectively; (2.23 +/- 0.46) x 10(-12), (1.95 +/- 0.50) x 10(-12), and (6.14 +/- 1.38) x 10(-12) for the reaction of NO(3) with EGMVE, EGDVE, and DEGDVE, respectively; and (2.02 +/- 0.41) x 10(-16), (1.69 +/- 0.41) x 10(-16), and (2.70 +/- 0.56) x 10(-16) for ozonolysis of EGMVE, EGDVE, and DEGDVE, respectively. Using the kinetic rate data, tropospheric lifetimes for EGMVE, EGDVE, and DEGDVE with respect to their reactions with OH, NO(3), and ozone have been estimated for typical ambient air concentrations of these oxidants.

Formation and emissions of carbonyls during and following gas-phase ozonation of indoor materials

Ozone concentrations that are several orders of magnitude greater than typical urban ambient concentrations are necessary for gas-phase ozonation of buildings, either for deodorization or for disinfection of biological agents. However, there is currently no published literature on the interaction of building materials and ozone under such extreme conditions. It would be useful to understand, for example in the case of building re-occupation planning, what types and amounts of reaction products may form and persist in a building after ozonation. In this study, 24 materials were exposed to ozone at concentrations of 1000 ppm in the inlet stream of experimental chambers. Fifteen target carbonyls were selected and measured as building ozonation by-products (BOBPs). During the 36 h that include the 16 h ozonation and 20 h persistence phase, the total BOBP mass released from flooring and wall coverings ranged from 1 to 20 mg m −2, with most of the carbonyls being of lower molecular weight (C 1–C 4). In contrast, total BOBP mass released from wood-based products ranged from 20 to 100 mg m −2, with a greater fraction of the BOBPs being heavier carbonyls (C 5–C 9). The total BOBP mass released during an ozonation event is a function of both the total surface area of the material and the BOBP emission rate per unit area of material. Ceiling tile, carpet, office partition, and gypsum wallboard with flat latex paint often have large surface areas in commercial buildings and these same materials exhibited relatively high BOBP releases. The greatest overall BOBP mass releases were observed for three materials that building occupants might have significant contact with: paper, office partition, and medium density fiberboard, e.g., often used in office furniture. These materials also exhibited extended BOBP persistence following ozonation; some BOBPs (e.g., nonanal) persist for months or more at emission rates large enough to result in indoor concentrations that exceed their odor threshold.

The Emissions of Major Aromatic Voc as Landfill Gas from Urban Landfill Sites in Korea

In this study, concentrations of major aromatic VOCs were determined from landfill gas (LFG) at a total of five municipal landfill sites in Korea including Nan Ji (NJ), Woon Jung (WJ), Sam Poong (SP), Hoei Chun (HC), and No Hyung (NH). The concentration levels of those VOC were found to be significantly different, mainly as a function of such a parameter as landfill aging. The VOC concentrations measured from the unclosed landfill sites (e.g., WJ) were characterized by exceedingly high values above a few tens of ppm. However, the results of the abandoned site (e.g., SP) were about three orders of magnitude lower than the others so as to merely exceed the typical ambient concentration levels. It was most striking to find a systematic dominance of toluene over other aromatic VOC under most circumstances. The LFG flux values of all aromatic VOC and the four specific major ones (termed as BTEX: benzene, toluene, ethylbenzene, and xylene) were also computed for each vent pipe from all study sites using their concentrations and the concurrently determined environmental parameters. The results, if calculated in terms of the average BTEX quantity emitted per vent pipe, showed that the magnitude of their emissions can vary substantially, with the values ranging from 0.05 (SP) to 49.2 kg yr(-1) (WJ in wintertime). The LFG flux values of aromatic VOC, when compared to the contribution of non-methane hydrocarbons (NMHC), were able to explain a constant, but minor, proportion of the LFG carbon budget.

Air contaminant exposures during the operation of lawn and garden equipment

The US Environmental Protection Agency (EPA) initiated the Small Engine Exposure Study (SEES) to evaluate potential exposures among users of small, gasoline-powered, non-road spark-ignition (SI) lawn and garden engines. Equipment tested included riding tractors, walk-behind lawn mowers, string trimmers, and chainsaws. Personal and background air quality measurements were collected on equipment operators for carbon monoxide (CO), particulate matter <or=2.5 microm in aerodynamic diameter (PM(2.5)), volatile organic compounds (VOCs), and aldehydes. PM(2.5) measurements included continuous and integrated mass, elemental and organic carbon (EC/OC), and trace metals. Aldehyde measurements included speciation for formaldehyde and acetaldehyde. The results demonstrated that equipment operators can experience elevated exposures to CO, PM(2.5) and air toxics while operating these engines. Ten-second average CO personal exposures spanned over two orders of magnitude, with short-term concentrations exceeding 120 p.p.m. for some engine applications tested. PM(2.5) concentrations averaged over each engine test period also spanned two orders of magnitude. The results also suggest that health standards, such as the CO and PM(2.5) National Ambient Air Quality Standards (NAAQS), may be exceeded for certain equipment types under certain operating scenarios. Aldehyde measurements suggested exposures from primary engine emissions that exceed typical ambient concentrations, but do not exceed occupational health standards. Continuous exposure measurements illustrated the important role of the operator's activity and environmental conditions in affecting exposure levels.

Health effects of particles in ambient air

Typical ambient particle concentrations for PM10 (PM2.5) in Germany are in the range of 10-45 (10-30) microg/m3 as annual mean and 50-200 (40-150) microg/m3 as maximum daily mean. The ratio of PM2.5/PM10 generally amounts between 0.7 and 0.9. During the past 10 years many new epidemiological and toxicological studies on health effects of particulate matter (PM) have been published. In summary, long-term exposure against PM for years or decades is associated with elevated total, cardiovascular, and infant mortality. With respect to morbidity, respiratory symptoms, lung growth, and function of the immune system are affected. Short-term studies show consistant associations of exposure to daily concentrations of PM with mortality and morbidity on the same day or the subsequent days. Patients with asthma, COPD, pneumonia, and other respiratory diseases as well as patients with cardio-vascular diseases and diabetes are especially affected. The strongest associations are found for PM2.5 followed by PM10, with no indication of a threshold value for the health effects. The data base for ultra fine particles is too small for final conclusions. The available toxicological data support the epidemiological findings and give hints as to the mechanisms of the effects. The working group concludes that a further reduction of the limit values proposed for 2005 will substantially reduce health risks due to particulate air pollution. Because of the strong correlation of PM10 with PM2.5 at most German sites there is no specific need for limit values of PM2.5 for Germany in addition to those of PM10.