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Atmospheric Environment (v.40, #27)

Editorial board (pp. i).

Nominations sought for the 2006 Haagen-Smit Prize (pp. 5111-5111).

Similarities of boundary layer ventilation and particulate matter roses by Matthew Rigby; Roger Timmis; Ralf Toumi (pp. 5112-5124).

Pollution wind sector or rose analyses show that under South-Easterly winds, many areas of the UK experience an increase in mean airborne particulate matter concentration of up to 30%over the average for all directions. This is often attributed solely to long-range transport of pollutants from continental Europe. Here, we present a rose analysis that suggests an additional influence of boundary layer ventilation. The directional increase in pollutant concentration is found to coincide with a 45–55%reduction in ventilation, obtained from ECMWF reanalysis. The reduced ventilation will increase the concentration of locally emitted particulate matter. This effect is explained by low average South-Easterly wind speeds, and advection of high-level warm air from continental Europe, which stabilises the boundary layer, and reduces the boundary layer height. A similar dependence of ventilation on wind direction was found across most of the world, so that a similar effect on pollution roses may be present at most locations. The high number of particulate matter exceedance days for Easterly flow was not found to be associated with a high frequency of extremely low ventilation conditions, suggesting that ventilation alone cannot explain these events.

Keywords: Air quality; Wind sector analysis; Reanalysis; Mixing height; PM10

Vertical profiles and receptor modeling of volatile organic compounds over Southeastern Mexico City by Wohrnschimmel Henry Wöhrnschimmel; Marquez Claudia Márquez; Violeta Mugica; Werner A. Stahel; Johannes Staehelin; Cardenas Beatriz Cárdenas; Salvador Blanco (pp. 5125-5136).

Tethered balloon flights were carried out over Southeastern Mexico City in April 2003, providing vertical profiles of ozone (0–1000m above ground) and volatile organic compounds (VOCs, 0–200m above ground). The objective of this study was to provide insight into the processes that drive ozone formation in Mexico City. In this paper, we discuss the atmospheric chemistry, emission sources and transport processes that influence the observed profiles. Characteristic ozone profiles were measured in the morning with the highest concentrations recorded in the residual layer. Maximum ozone concentrations, as high as 170ppb, were measured at ground level in the afternoon. For the shape of VOC vertical profiles, no unique patterns were found. High concentrations were measured for propane, butane and toluene. Diurnal variations in VOC concentrations imply a strong effect of vertical dilution with an increasing mixing layer. Two different receptor models were used to relate observed VOC concentrations to emission sources. Results from a chemical mass balance (CMB) model suggest that the main contributors to total VOCs and the related ozone formation potential are gasoline vehicle exhaust and liquefied petroleum gas (LPG). A linear unmixing analysis reproduced satisfactorily the measured source profiles of the main sources. The relative source activities calculated by the CMB and the linear unmixing models coincide well for the LPG contribution; however, the vehicle exhaust contribution is underestimated and solvent emissions are overestimated by linear unmixing relative to the CMB model.

Keywords: Air pollution; Volatile organic compounds; Ozone; Chemical mass balance; Linear unmixing analysis

Ammonia volatilization from artificial dung and urine patches measured by the equilibrium concentration technique (JTI method) by Saarijarvi K. Saarijärvi; P.K. Mattila; Virkajarvi P. Virkajärvi (pp. 5137-5145).

The aim of this study was to investigate the dynamics of ammonia (NH₃) volatilization from intensively managed pastures on a soil type typical of the dairy production area in Finland and to clarify the effect of rainfall on NH₃ volatilization. The study included two experiments. In Experiment 1 the total amount of NH₃–N emitted was calculated based on the annual surface coverage of dung (4%) and urine (17%). The application rate of total N in the simulated dung and urine patches was approximately 47gNm⁻² and 113gNm⁻², respectively. In Experiment 1 the general level of NH₃ emissions from the urine patches was high and the peak volatilization rate was 0.54gNH₃–Nm⁻²h⁻¹. As expected, emissions from the dung pats were clearly lower with a maximum rate of 0.10gNH₃–Nm⁻²h⁻¹. The total emission calculated for the whole pasture area (stocking rate four cowsha⁻¹y⁻¹, urine coverage 17% and dung coverage 4%) was 16.1kgNH₃–Nha⁻¹. Approximately 96% of the total emission originated from urine. In Experiment 2 we measured the emissions from urine only and the treatments on the urine patches were: (1) no irrigation, (2) 5+5mm and (3) 20mm irrigation. The peak emission rates were 0.13, 0.09 and 0.04gNH₃–Nm⁻²h⁻¹ and the total emissions were 6.9, 3.0 and 1.7kgNH₃–Nha⁻¹, for treatments (1), (2) and (3), respectively. In both measurements over 80% of the total emission occurred during the first 48h and there was a clear diurnal rhythm. Increasing rainfall markedly decreased NH₃ emission. Volatilization was highest with dry and warm soil. The JTI method appeared to be suitable for measuring NH₃ volatilization in this kind of experiment. According to our results, the importance of pastures as a source of NH₃ emission in Finland is minor.

Keywords: Ammonia; Nitrogen; Pasture; Gaseous emissions; Dairy cattle; Finland

Characteristics of aerosol observed during two severe haze events over Korea in June and October 2004 by Kwon Ho Lee; Y.J. Young Joon Kim; Min Jeong Kim (pp. 5146-5155).

Satellite, ground-based sunphotometer, and real-time carbon particle analyzer data were analyzed to evaluate the causes for two severer haze events observed during 9–12 June and 5–8 October 2004 in Korea. The first event was clearly affected by long-range transported smoke from a multitude of fires in East China. Very high aerosol optical thickness (AOT) levels over 2.0 and elevated surface PM₁₀ concentrations up to 256μgm⁻³ were observed during the first haze event. Still very high PM₁₀ mass loadings were observed during the second haze event compared to the first haze event ones with different source characteristics. Due to different origin and pathway of the haze plume, wide difference in the organic/elemental carbon ratio was measured between the two events. It is believed that the aerosol in the first event was dominated by the carbon particles from burning areas in East China while that in the second event was dominated by primary carbon particles from the pollution from large urban areas in China.

Keywords: Haze; Satellite; Aerosol optical thickness; PM; ₁₀; Carbonaceous particles; Korea/China

Evaluation of the ability of indicator species ratios to determine the sensitivity of ozone to reductions in emissions of volatile organic compounds and oxides of nitrogen in northern California by Jinyou Liang; Bruce Jackson; Ajith Kaduwela (pp. 5156-5166).

Six indicator ratios were evaluated for their regulatory application in California using three-dimensional (3-D) photochemical transport modeling output for an ozone episode during 31 July–2 August 2000. The evaluation was based on four criteria with increasing usefulness for 8-h ozone controls. The four criteria can be briefly described as: (1) smooth functional behavior between ozone benefits/disbenefits and the magnitude of the indicator ratio, (2) narrow separation between beneficial and detrimental regimes for oxides of nitrogen (NO _x) emissions controls, (3) narrow transition regime between where volatile organic compound controls are more beneficial than NO _x controls and vice versa, and (4) invariance of these transition ranges in time and space. None of the indicator ratios met all criteria. We present results for five sub-regions in northern California. The transition regime for criteria (3) was found to be much wider than that for criteria (2) for all sub-regions. Hence, the indicator ratios may be of only limited usefulness in determining precursor limitations and might be more valuable in diagnosing if NO _x controls are beneficial or detrimental.

Keywords: Ozone control; Precursor limitations; Photochemical transport model; CCOS; OBM

Impact of vertical atmospheric structure on Beijing aerosol distribution by Benjamin Guinot; J.-C. Jean-Claude Roger; H Hélène Cachier; Wang Pucai; Bai Jianhui; Yu Tong (pp. 5167-5180).

In August 2004, original informations on Beijing aerosol layers were obtained downtown from experiments achieved during clear and polluted days along the IAP 325-m meteorological tower and a micro-pulse LIDAR operating at BMEMC. Beijing urban boundary layer (UBL) is seen to follow the expected diurnal pattern with low height values at night (80±50m) and much higher values (up to 3000m) at daytime. An original process of temperature profiles is shown to closely reconstruct the UBL and sub-layer evolution. UBL vertical extension becomes significant after a short transition period at 10:00 during which at all the tower levels, wind speed increases and wind direction changes dramatically from the synoptic northerly flow to almost the opposite direction (SSW). Additional data from background stations show pollution episodes that may be related to horizontal transport at low altitude during the morning or evening transition periods. Vertical profiles of black carbon (BC) and particle number concentration (N) and LIDAR signal evidence the formation of accumulation layers at 60m and 90m probably related to the urban canopy. Using the N/BC ratio, an important chemical reactivity may be observed within the accumulation layers and is still distinguishable during cloudy weather. Reactivity in the vertical column appears to increase with altitude, which might point to the significance of solar radiation shielding by particles. Chemical analyses confirm, in the morning, the presence of a very distinct layer at the top of the tower and show, in the afternoon, a significant mixing (17%) between the UBL and the regional flow above.

Keywords: Urban aerosols; Aerosol vertical distribution; Urban boundary layer; Urban canopy; Accumulation layer; Radiation shielding

Modeling of episodic particulate matter events using a 3-D air quality model with fine grid: Applications to a pair of cities in the US/Mexico border by Y.-J. Yu-Jin Choi; Peter Hyde; H.J.S. Fernando (pp. 5181-5201).

High (episodic) particulate matter (PM) events over the sister cities of Douglas (AZ) and Agua Prieta (Sonora), located in the US–Mexico border, were simulated using the 3D Eulerian air quality model, MODELS-3/CMAQ. The best available input information was used for the simulations, with pollution inventory specified on a fine grid. In spite of inherent uncertainties associated with the emission inventory as well as the chemistry and meteorology of the air quality simulation tool, model evaluations showed acceptable PM predictions, while demonstrating the need for including the interaction between meteorology and emissions in an interactive mode in the model, a capability currently unavailable in MODELS-3/CMAQ when dealing with PM. Sensitivity studies on boundary influence indicate an insignificant regional (advection) contribution of PM to the study area. The contribution of secondary particles to the occurrence of high PM events was trivial. High PM episodes in the study area, therefore, are purely local events that largely depend on local meteorological conditions. The major PM emission sources were identified as vehicular activities on unpaved/paved roads and wind-blown dust. The results will be of immediate utility in devising PM mitigation strategies for the study area, which is one of the US EPA-designated non-attainment areas with respect to PM.

Keywords: Particulate matter; 3D air quality model; Dust; High winds; US/Mexico border; Semi-arid area

Modeling retained water content in measured aerosol mass by Mizuo Kajino; Wilfried Winiwarter; Hiromasa Ueda (pp. 5202-5213).

The contribution of liquid water to measured aerosol mass was estimated using a numerical approach applied to European measurement data. Aerosol mass is determined after conditioning of the filter under dry conditions for a predefined period according to a standard procedure. After this procedure, water in aerosols is assumed to be at very low concentrations. However, we find indications that the equilibrium of aerosol is not fully established and water is not completely evaporated after the drying operation. To estimate the aerosol humidity, a mass transfer coefficient was derived for evaporation from the filters. Data from a few available measurements of aerosol humidity were applied with a numerical kinetic approach, using thermodynamic equilibrium as boundary conditions. The calculated coefficient ranged from 10⁻⁵ to 10⁻⁴ (s⁻¹), with an average value of 3.2×10⁻⁵s⁻¹. Using this average value the expected water content of aerosol was assessed for sites in Austria. Most of the samples are expected to still contain 1–5% water. In winter, the air is humid and the concentration of inorganic hygroscopic compounds is also high, resulting in high uptake of water from the air. Under such conditions, approximately 70% of unidentified non-carbonaceous components, or about 10% of PM_2.5 mass, were considered to be water.

Keywords: Aerosol water; Sampling artifacts; Drying operation; Mass transfer approach; Semi-empirical and theoretical approaches; Multi-component equilibrium model

A high-resolution NO _x emission factor model for North American motor vehicles by Rakesh B. Singh; James J. Sloan (pp. 5214-5223).

Criteria air contaminant inventories in Canada show that approximately 60% of NO _x is produced from the transportation sector alone. NO₂, which is present at higher levels in the winter than in the summer, has been identified as the main pollutant responsible for non-traumatic deaths and hospitalization in Canadian cities. Therefore, accurate emission estimates of vehicle-generated NO _x are needed, especially at the micro-scale level. The MOBILE emission model, which is widely used in Canada, provides only aggregated emission factors at very low resolution. Many studies have shown that MOBILE emission data are unreliable for many applications—particularly for air-quality modelling. In contrast to the aggregated nature of the MOBILE data, the new disaggregated model,MicroFacNO _x, uses time-dependent site-specific vehicle fleet information to calculate emission factors at high spatial and temporal resolution.MicroFacNO _x evaluation in a range of traffic fleet and meteorological conditions shows very encouraging results. Sensitivity analyses of the model reveal that its results depend on traffic fleet composition, speed and ambient temperature.MicroFacNO _x results are suitable for use in human exposure assessment and by city planners in decision making for growth management. The effect of vehicle-related NO _x on ozone in the vicinity of a large urban area is a good example of an unsolved problem that would benefit from theMicroFacNO _x modelling approach.

Keywords: Micro-scale; Emission model; Mobile sources; Air-quality model; Human exposure

Comparison of oil and fuel particle chemical signatures with particle emissions from heavy and light duty vehicles by Matthew T. Spencer; Laura G. Shields; David A. Sodeman; Stephen M. Toner; Kimberly A. Prather (pp. 5224-5235).

In order to establish effective vehicle emission control strategies, efforts are underway to perform studies which provide insight into the origin of the source of vehicle particle emissions. In this study, the mass spectral signatures of individual particles produced from atomized auto and diesel oil and fuel samples were obtained using aerosol time-of-flight mass spectrometry (ATOFMS). The major particle types produced by these samples show distinct chemistry, falling into several major categories for each sample. Lubricating oils contain calcium and phosphate based additives and although the additives are present in low abundance (∼1–2% by mass), calcium and phosphate ions dominate the mass spectra for all new and used oil samples. Mass spectra from used oil contain more elemental carbon (EC) and organic carbon (OC) marker ions when compared to new oils and exhibit a very high degree of similarity to heavy duty diesel vehicle (HDDV) exhaust particles sampled by an ATOFMS. Fewer similarities exist between the used oil particles and light duty vehicle (LDV) emissions. Diesel and unleaded fuel mass spectra contain polycyclic aromatic hydrocarbon (PAH) molecular ions, as well as intense PAH fragment ions²⁵(C₂H)⁻,⁴⁹(C₄H)⁻, and inorganic ions²³Na⁺,³⁹K⁺,⁹⁵(PO₄)⁻. Unleaded fuel produced spectra which contained Na⁺ and K⁺; likewise, LDV particle emission spectra also contained Na⁺ and K⁺. Comparing oil and fuel particle signatures with HDDV and LDV emissions enhances our ability to differentiate between these sources and understand the origin of specific marker ions from these major ambient particle sources.

Keywords: Aerosol; ATOFMS; Diesel; Oil; Climate

Tracer gas transport under mixed convection conditions in an experimental atrium: Comparison between experiments and CFD predictions by Buvaneswari Jayaraman; Elizabeth U. Finlayson; Michael D. Sohn; Tracy L. Thatcher; Phillip N. Price; Emily E. Wood; Richard G. Sextro; Ashok J. Gadgil (pp. 5236-5250).

We compare computational fluid dynamics (CFD) predictions using a steady-state Reynolds Averaged Navier–Stokes (RANS) model with experimental data on airflow and pollutant dispersion under mixed-convection conditions in a 7×9×11m high experimental facility. The Rayleigh number, based on height, was O(10¹¹) and the atrium was mechanically ventilated. We released tracer gas in the atrium and measured the spatial distribution of concentrations; we then modeled the experiment using four different levels of modeling detail. The four computational models differ in the choice of temperature boundary conditions and the choice of turbulence model. Predictions from a low-Reynolds-number k- ε model with detailed boundary conditions agreed well with the data using three different model-measurement comparison metrics. Results from the same model with a single temperature prescribed for each wall also agreed well with the data. Predictions of a standard k- ε model were about the same as those of an isothermal model; neither performed well. Implications of the results for practical applications are discussed.

Keywords: Mixed convection; Indoor pollutant dispersion; Turbulence model; Atria

A field study of visual perception of complex natural targets through atmospheric haze by naïve observers by Ronald C. Henry (pp. 5251-5261).

An air quality–visibility perception study was carried out in southern California in July and August of 2002. The study was designed to make simultaneous state-of-the-art measurements of human perception, physical light intensities from natural targets, and particle scattering coefficient of the atmosphere. The purpose of the study was to obtain data needed to estimate the probability of seeing a change in haze due to a decrease in extinction coefficient of the atmosphere. The basic results of the visibility perception study are given. The focus is on quantitative measurements of human perception of lightness, hue and chroma (or colorfulness) of natural and artificial targets determined by an advanced color matching instrument and training protocol that made it possible to use naïve observers. The lightness, chroma, and hue calculated from the CIE X, Y, and Z measured by a 16-bit industrial imaging photometer are compared to those actually reported by the observers under varying levels of haze. The results are consistent with the results of two previous visibility perception studies carried out in national parks in the USA.

Keywords: Visibility; Color; Perception; Los Angeles; California; Haze; Transparancy

Bottom-up estimate of biomass burning in mainland China by Xiaoyuan Yan; Toshimasa Ohara; Hajime Akimoto (pp. 5262-5273).

To assess the contribution of biomass burning to the emissions of atmospheric trace species in China, we estimated various biomass-burning activities using statistical data, survey data, expert estimates and a satellite data set. Fuel wood and crop residue burned as fuel and in the field are the major sources of biomass burning in China, accounting for nearly 90% of the total biomass burning on dry weight base. Field burning of crop residue estimated from satellite burned area is less than 1% of that estimated from ground survey data; because of this and because biofuel is burned indoor, the majority of biomass burning in China is not seeable from satellite. Statistical data showed that the occurrence of forest fire in China has decreased dramatically since the 1980s; however, the forest fire area detected by satellites in 2000 was 13 times that shown by statistics. Grassland fires are a minor source of biomass burning in China. We estimated carbon monoxide (CO) emission from open biomass burning (field burning of crop residue and forest and grassland fires) to be 16.5Tg in 2000, with a 90% uncertainty range of 3.4–34Tg. Uncertainties in CO emission factors, especially for field burning of crop residue, contributed much more to the variance than those in the activity data. This suggests the importance of narrowing the uncertainty range of emission factors.

Keywords: Biofuel; Forest fires; Fate of crop residue; Field burning; Emissions

Influence of the PBL scheme on high-resolution photochemical simulations in an urban coastal area over the Western Mediterranean by Perez Carlos Pérez; Jimenez Pedro Jiménez; Oriol Jorba; Michael Sicard; J.M. José M. Baldasano (pp. 5274-5297).

Planetary boundary layer (PBL) and land-surface processes have critical implications for air quality simulations. This contribution analyses the influence of three different surface/PBL schemes from the MM5 mesoscale meteorological model on the predicted photochemical pollutant concentrations using high-resolution EMICAT2000 emission model and Models-3/CMAQ chemical transport model. The Gayno–Seaman (GS), the Medium Range Forecast (MRF), and the Pleim–Chang (PC) PBL schemes are considered. The simulations focus on a complex coastal urban area (Barcelona Geographical Area) located in the Western Mediterranean for a typical summertime situation characterised by the absence of large-scale forcing. The particularities of the area require high spatial (1km) resolution. Air quality, meteorological and lidar data are used for the evaluation of the results.PBL height inputs have been considered as diagnosed by MM5 and re-diagnosed by the MCIP meteorological pre-processor of Models-3/CMAQ. Several variables playing an essential role in the concentrations of air pollutants, such as PBL height, temperature, and wind speed and direction, are analysed. Important differences are observed in GS scheme depending on the method used in the PBL height estimation. MRF and PC present similar results. Modelled daily maximum pollutants’ concentrations vary in magnitude and location in function of the PBL scheme. GS–MM5 scenario presents the lowest PBL heights, the highest surface temperatures and the weakest winds during daytime, which provokes an enhanced O₃ formation. The higher concentrations of NO _x in the GS–MM5 scheme (which are caused mainly by the lower PBL height) provokes a higher depletion of O₃, which yields to the lower concentrations of this pollutant during nighttime in Barcelona downtown.For regulatory purposes, the model tends to underestimate the photochemical formation in the area of study due to an underestimation of VOCs emissions in an VOC-limited area as Barcelona. The lower PBL height shown by GS taken from MM5, as well as the increase in the temperature and the weaker winds over coastal areas (that allow the accumulation of photochemical pollutants) promotes the O₃ concentration and improves the statistical scores of GS–MM5 scenario.

Keywords: Mixing height; Air quality modelling; MM5; Models-3/CMAQ; Complex terrain

Observation on soil water content and wind speed in Erlianhot, a dust-source area in northern China by Ning Li; Wei Gu; Zixuan Du; Zhangjun Li; Peiguo Song (pp. 5298-5303).

In this manuscript, the authors investigated the spring dust storm event in northern Inner Mongolia of China and the relationship between wind speed and soil water content in dust storm events and non-dust storm events, as well as the impact of the precipitation on the soil water content variations. The seasonal variations of precipitation are remarkable, the spring precipitations account only for 15% of the total amount in the whole year. The soil water content is fairly well consistent with precipitation amount. In addition, the soil water contents show a good relationship with wind speeds, which is supported by the significantly negative correlations. But, the non-dust storm events shows no the evident relationship. It implies that soil water content can modulate dust storm activity through influencing the wetness of land surface under the same cold highs. The obvious variation in non-dust storms was the greater increase of soil water content rather than the decrease of wind speed. Both of them had variation with a weaker swing. However, for the status of dust storm, wind speeds had larger wave and soil water content shows stability and lower value. The wetness change on land surface, at least partly, is responsible for the secular reducing dust storm events in the study area.

Keywords: Dust storms; Inner Mongolia; Wind speed; Soil water content

Comparison of spatial and temporal variations of aerosol optical thickness and particulate matter over Europe by R.B.A. Koelemeijer; C.D. Homan; J. Matthijsen (pp. 5304-5315).

To mitigate the harmful effect of particulates on human health, EU wide limit values for concentrations have been set. However, particulate matter (PM) measurements suffer from substantial uncertainty because PM is difficult to measure on a routine basis, which is necessary for monitoring compliance. Moreover, different measurement and calibration methods are used in the many air-quality networks in Europe. Consequently, the understanding of PM levels over Europe as a whole is rather limited. We aim to improve this situation by making use of additional information from satellite observations. As a first step, we present here a comparison for Europe of spatio-temporal variations of PM with those of aerosol optical thickness (AOT) measured by the MODIS satellite instrument, for 2003. The MODIS measurements clearly show the major aerosol source regions in Northern Italy, Southern Poland, and the Belgium/Netherlands/Ruhr area, as well as individual large cities and industrialised valleys (Rhone, Danube). The spatial correlation between yearly average PM10 and AOT is 0.6 for rural background stations.The seasonal variation of AOT and PM is distinctly different, however. Throughout most of Europe, the AOT as measured by MODIS has a clear minimum in the winter months. The seasonal variation in PM differs across Europe, and at many locations the seasonal variation is less marked than that of the AOT. Consequently, the correlation between one-year time-series of AOT with PM10/PM2.5 is low (0.3). The correlation between PM and AOT is improved when the AOT is divided by the boundary layer height and, to a lesser extent, when it is corrected for growth of aerosols with relative humidity. In that case, the average correlation is 0.5 (PM10) and 0.6 (PM2.5), averaged over rural and (sub) urban background stations. These results indicate that AOT measurements can be useful to improve the monitoring of PM distributions over Europe.

Keywords: Particulate matter; AIRBASE; Aerosol optical thickness; MODIS; Europe

Levoglucosan as an atmospheric tracer for woodsmoke by Timothy B. Jordan; Andrew J. Seen; Geraldine E. Jacobsen (pp. 5316-5321).

Ambient air samples collected in Launceston, Australia, were analysed for a range of organic compounds to determine a suitable tracer for assessing the contribution of woodburning to air pollution. Levoglucosan (1,6-anhydro- β-d-glucopyranose), a major constituent of smoke from biomass burning, was shown to be stable during atmospheric transport and present at expected levels, however, many other woodsmoke compounds, including methoxyphenols, were found to be severely depleted compared to that expected from woodsmoke. The average emission factor of levoglucosan from woodburning across the Launceston airshed was determined by correlation of the levoglucosan concentration in air with PM₁₀ levels and correction for the biomass content of PM₁₀ using radiocarbon (¹⁴C) measurements. Woodsmoke was estimated to comprise about 95% of wintertime air pollution in Launceston, and the resulting average levoglucosan woodburning emission factor of around 140mgg⁻¹ particulate matter was found to be consistent with previously determined woodheater emissions. This method represents a simple, cheap, and readily accessible means for quantifying the contribution of woodsmoke to atmospheric pollution.

Keywords: Biomass combustion; Radiocarbon; Carbon-14; Woodheater; Air pollution

Comment on “Measuring self-pollution in school buses using a tracer gas technique�? by Behrentz et al. by Robert Ireson; Michael Easter; Michael Lakin; Charles Lapin; Gerald Chase (pp. 5322-5324).

Reply to comment on “measuring self-pollution in school buses using a tracer gas technique�? by Eduardo Behrentz; Lisa D. Sabin; Arthur M. Winer; Dennis R. Fitz; David V. Pankratz; Steven D. Colome; Scott A. Fruin (pp. 5325-5327).

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Atmospheric Environment (v.40, #27)