Atmospheric Environment (v.37, #38)
Editorial board (i).
List for forthcoming papers (I-II).
Effect of ventilation systems and air filters on decay rates of particles produced by indoor sources in an occupied townhouse by Cynthia Howard-Reed; Lance A Wallace; Steven J Emmerich (5295-5306).
Several studies have shown the importance of particle losses in real homes due to deposition and filtration; however, none have quantitatively shown the impact of using a central forced air fan and in-duct filter on particle loss rates. In an attempt to provide such data, we measured the deposition of particles ranging from 0.3 to 10 μm in an occupied townhouse and also in an unoccupied test house. Experiments were run with three different sources (cooking with a gas stove, citronella candle, pouring kitty litter), with the central heating and air conditioning (HAC) fan on or off, and with two different types of in-duct filters (electrostatic precipitator and ordinary furnace filter). Particle size, HAC fan operation, and the electrostatic precipitator had significant effects on particle loss rates. The standard furnace filter had no effect. Surprisingly, the type of source (combustion vs. mechanical generation) and the type of furnishings (fully furnished including carpet vs. largely unfurnished including mostly bare floor) also had no measurable effect on the deposition rates of particles of comparable size. With the HAC fan off, average deposition rates varied from 0.3 h−1 for the smallest particle range (0.3–0.5 μm) to 5.2 h−1 for particles greater than 10 μm. Operation of the central HAC fan approximately doubled these rates for particles <5 μm, and increased rates by 2 h−1 for the larger particles. An in-duct electrostatic precipitator increased the loss rates compared to the fan-off condition by factors of 5–10 for particles <2.5 μm, and by a factor of 3 for 2.5–5.0 μm particles. In practical terms, use of the central fan alone could reduce indoor particle concentrations by 25–50%, and use of an in-duct ESP could reduce particle concentrations by 55–85% compared to fan-off conditions.
Keywords: Fine particles; Coarse particles; Deposition; Filtration; Residential indoor air quality;
Particle-associated polycyclic aromatic hydrocarbons in urban air of Hong Kong by H Guo; S.C Lee; K.F Ho; X.M Wang; S.C Zou (5307-5317).
PM2.5 and PM10 samples were collected at two sampling sites in Hong Kong in wintertime from November 2000 to March 2001 and in summertime from June to August 2001. The concentrations of 16 selected polycyclic aromatic hydrocarbons (PAHs) in aerosols were quantified. Spatial and seasonal variations of PAHs were characterized. The dominated PAHs in PM2.5 and PM10 included benzo[b]fluoranthene, pyrene, fluoranthene, indeno[1,2,3-cd]pyrene and chrysene, accounting for 50–82% of total PAHs. The sum of 16 PAHs in PM2.5 at roadside ranged from 3 to 330 ng/m3, and in PM10 between 5 and 297 ng/m3, whereas at a residential/industrial/commercial site, the total PAHs in PM2.5 was from 0.5 to 122 ng/m3, and 2–269 ng/m3 in PM10. Results indicated that most of the PAHs were in the PM2.5 fraction. Spatial variations were predominantly due to the difference of source strength. For both PM2.5 and PM10, the total PAHs at PU site was higher than that at KT site. The average concentrations of individual PAHs in aerosols at PU site were also higher than that at KT site. Higher winter PAHs concentrations and lower summer concentrations were observed at the two sites. Higher winter PAHs concentrations were mainly caused by local emission sources superimposed by highly polluted air masses from Mainland China. The lower summer PAHs concentrations were likely due to easier dispersion of air pollutants, washout effects and to a lesser extent, photo-degradation and higher percentage in the air in vapor phase. Potential sources of PAHs in aerosols were identified using the diagnostic ratios between PAHs and PCA analysis. At PU site, vehicular emissions were the main contributors of particle-associated PAHs, and stationary combustion sources may also contribute to the particulate PAHs. On the contrary, at the KT site, PAHs in aerosols were predominantly from gasoline and diesel engines.
Keywords: Polycyclic aromatic hydrocarbons; PM2.5; PM10; Diagnostic ratios; Hong Kong;
Nineteenth century Parisian smoke variations inferred from Eiffel Tower atmospheric electrical observations by R.G. Harrison; K.L. Aplin (5319-5324).
Atmospheric electrical measurements provide proxy data from which historic smoke pollution levels can be determined. This approach is applied to infer autumnal Parisian smoke levels in the 1890s, based on atmospheric electric potential measurements made at the surface and the summit of the Eiffel Tower (48.7°N, 2.4°E). A theoretical model of the development of the autumn convective boundary layer is used to determine when local pollution effects dominated the Eiffel Tower potential measurements. The diurnal variation of the Eiffel Tower potential showed a single oscillation, but it differs from the standard oceanic air potential gradient (PG) variations during the period 09–17 UT, when the model indicates that the Eiffel Tower summit should be within the boundary layer. Outside these hours, the potential changes closely follow the clean air PG variation: this finding is used to calibrate the Eiffel Tower measurements. The surface smoke pollution concentration found during the morning maximum was 60±30 μg m−3, substantially lower than the values previously inferred for Kew in 1863. A vertical smoke profile was also derived using a combination of the atmospheric electrical data and boundary layer meteorology theory. Midday smoke concentration decreased with height from 60 μg m−3 at the surface to 15 μg m−3 at the top of the Eiffel Tower. The 19th century PG measurements in both polluted and clean Parisian air present a unique resource for European air pollution and atmospheric composition studies, and early evidence of the global atmospheric electrical circuit.
Keywords: Aerosol pollution; Atmospheric potential gradient; Boundary layer; Historical data; Paris;
UCD 2001: an improved model to simulate pollutant dispersion from roadways by Tony Held; Daniel P.Y. Chang; Debbie A. Niemeier (5325-5336).
An improved dispersion model, UCD 2001, designed to estimate pollutant concentrations near roadways was developed and its performance evaluated. The UCD 2001 model internally represents a highway link as a three-dimensional array of point sources that simulates a roadway mixing zone which extends 2.5 m above a highway link. Dispersion from each point source is estimated with the Huang dispersion solution. The Huang equation is a simplified solution to the semi-empirical advection diffusion equation; its derivation permits vertical profiles of wind speed and eddy diffusivity in the boundary layer to be approximated by power law functions.The UCD 2001 model was calibrated with one-half of the General Motors (GM) SF6 tracer study data base and resulted in a selection of eddy diffusivity parameters that did not vary with ambient meteorology. This parameterization is consistent with several independent studies which indicate that the atmosphere is well-mixed and neutrally stratified immediately downwind of a roadway with significant vehicular activity.UCD 2001 model performance was evaluated and compared to the CALINE3 and CALINE4 dispersion models using the GM data base. UCD 2001 adequately simulates near parallel, low wind speed (less than 0.5 m/s) meteorological scenarios, whereas the CALINE models significantly over predict most receptor concentrations for these conditions. The UCD 2001 model results in approximately 80–90 percent reduction in squared residual error when compared to the CALINE3 and CALINE4 models. In addition, the UCD 2001 model exhibits better agreement in simulating the top forty observed concentrations than either CALINE model. Lastly, the UCD 2001 model requires less user input and modeler expertise than most roadway dispersion models, and should result in more consistent and robust pollutant field estimations.
Keywords: Intersection; Line-source; CALINE; Carbon monoxide; Dispersion; Gaussian;
Laboratory studies of ozone uptake on processed mineral dust by C.R. Usher; A.E. Michel; D. Stec; V.H. Grassian (5337-5347).
After atmospheric aging and processing, mineral dust particles are often coated with nitrates, sulfates, and organics. In this study, laboratory experiments were done to simulate possible changes in the reactivity of mineral dust particles after being processed or aged in the atmosphere. Initial uptake coefficients of ozone on processed and unprocessed dust were measured with a Knudsen cell reactor and the relative reactivities are compared. In particular, the reactive uptake of ozone with mineral oxide particles that had been pretreated by exposure to nitric acid, sulfur dioxide, and organics are compared to particles that had not been pretreated. In some cases, it was found that the reactivity of ozone with pretreated particles was significantly reduced whereas in other cases the reactivity was enhanced. For example, the reactive uptake of ozone decreased by approximately 70% for α-Al2O3 particles coated with a layer of nitrate from reaction with nitric acid compared to particles that did not have a nitrate coating, whereas pretreatment of α-Al2O3 with sulfur dioxide showed a 33% enhancement toward ozone reactivity. For organic coatings, it was determined that SiO2 particles functionalized with a C8-alkene displayed enhanced reactivity toward ozone by 40% relative to untreated SiO2, while SiO2 particles functionalized with a C8-alkane exhibited decreased reactivity by approximately 40% relative to untreated SiO2 particles. The reaction mechanism of ozone uptake with these particles is discussed, as well as the impact on the chemistry of ozone on coated mineral dust aerosol in the troposphere.
Keywords: Tropospheric ozone; Mineral aerosol; Knudsen cell; Kinetics; Heterogeneous reactions; Atmospheric processing;
The Research Triangle Park particulate matter panel study: PM mass concentration relationships by Ron Williams; Jack Suggs; Anne Rea; Kelly Leovic; Alan Vette; Carry Croghan; Linda Sheldon; Charles Rodes; Jonathan Thornburg; Ademola Ejire; Margaret Herbst; William Sanders (5349-5363).
The US Environmental Protection Agency has recently performed the Research Triangle Park Particulate Matter Panel Study. This was a 1-year investigation of PM and related co-pollutants involving participants living within the RTP area of North Carolina. Primary goals were to characterize the relationships between ambient and residential PM measures to those obtained from personal exposure monitoring and estimate ambient source contributions to personal and indoor mass concentrations. A total of 38 participants living in 37 homes were involved in personal, residential indoor, residential outdoor and ambient PM2.5 exposure monitoring. Participants were 30 non-smoking hypertensive African-Americans living in a low-moderate SES neighborhood (SE Raleigh, NC) and a cohort of eight individuals having implanted cardiac defibrillators (Chapel Hill, NC). Residential and ambient monitoring of PM10 and PM10–2.5 (coarse by differential) was also performed. The volunteers were monitored for seven consecutive days during each of four seasons (summer 2000, fall 2000, winter 2001, spring 2001). Individual PM2.5 personal exposure concentrations ranged from 4 to 218 μg m−3 during the study. The highest personal exposures were determined to be the result of passive environmental tobacco exposures. Subsequently, ∼7% of the total number of personal exposure trials were excluded to minimize this pollutant's effect upon the overall analysis. Results indicated that a pooled data set (seasons, cohorts, residences, participants) was appropriate for investigation of the basic mass concentration relationships. Daily personal PM2.5 mass concentrations were typically higher than their associated residential or ambient measurements (mean personal=23.0, indoor=19.1, outdoor=19.3, ambient=19.2 μg m−3). Mean personal PM2.5 exposures were observed to be only moderately correlated to ambient PM2.5 concentrations (r=0.39).
Keywords: Ambient air monitoring; Personal exposure monitoring; Susceptible subpopulations;
The Research Triangle Park particulate matter panel study: modeling ambient source contribution to personal and residential PM mass concentrations by Ron Williams; Jack Suggs; Anne Rea; Linda Sheldon; Charles Rodes; Jonathan Thornburg (5365-5378).
The Research Triangle Park (RTP) Particulate Matter (PM) Panel Study represented a 1-year investigation of personal, residential and ambient PM mass concentrations across distances as large as 70 km in central North Carolina. One of the primary goals of this effort was to estimate ambient PM2.5 contributions to personal and indoor residential PM mass concentrations. Analyses indicated that data from the two distinct non-smoking subject populations totaling 38 individuals and 37 residences could be pooled. This resulted in nearly 800 data points for each variable. A total of 55 measurements believed to have been potentially influenced by personal or residential exposure to passive environmental tobacco smoke were not included in the analysis database. Variables to be examined included C ig (concentration of indoor generated PM), E ig (personal exposure to indoor generated PM), F inf (ambient PM infiltration factor), and F pex (personal exposure to PM of ambient origin factor). Daily air exchange rates (AER) were measured and statistical modeling to derive estimates of particle penetration (P) and particle deposition (k) factors was performed. Seasonality, cohort grouping, participant or combinations of these variables were determined not to be significant influences in estimating group infiltration factors. The mean (±std) mixed model slope estimates were AER=0.72±0.63, P=0.72±0.21, k=0.42±0.19, and F inf=0.45±0.21. These variables were then used in a number of mixed effects models having varying features of single, random or fixed intercepts and/or slopes to determine the most appropriate means of estimating ambient source contributions to personal and residential settings. A mixed model slope for F pex (±SE) was 0.47±0.07 using the model with the highest degree of fit.
Keywords: Source contribution; Infiltration factor; Particle penetration;
Development of hourly probabilistic utility NO x emission inventories using time series techniques: Part I—univariate approach by Amr Abdel-Aziz; H.Christopher Frey (5379-5389).
Historical data regarding hourly variability in coal-fired power plant unit emissions based upon continuous emission monitoring enables estimation of the likely range of possible values in the near future for purposes of air quality modeling. Analyses were conducted for 32 units for a base case in 1995, an alternative 1998 case, and a 2007 future scenario case. Hourly inter-unit uncertainty was assumed to be independent. Univariate stochastic time series models were employed to quantify hourly uncertainty in capacity and emission factors. Ordinary least-squares regression models were used to quantify hourly uncertainty in heat rate. The models were used to develop an hourly probabilistic emission inventory for a 4-day period. There was significant autocorrelation for time lags 1, 2, 23, and 24 for the capacity and emission factor and a 24 h cyclical pattern for the capacity factor. The uncertainty ranges for hourly emissions were found to vary for different hours of the day, with 95% probability ranges of typically ±20–40% of the mean. For the 1995 case, the 95% confidence interval for the daily inventory was 510–633 t/d, representing approximately ±10% uncertainty with respect to the average value of 576 t/d. Inter-annual changes in the mean and variability were assessed by comparison of 1998 data with 1995 data. The daily inventory for the 2007 scenario had an uncertainty range of ±8% of the average value of 175 t/d. The substantial autocorrelation in capacity and emission factor, and the cyclic effect for capacity factor, indicate the importance of accounting for time series effects in estimation of uncertainty in hourly emissions. Additional work is recommended to account for inter-unit dependence, which is addressed in Part 2.
Keywords: Autocorrelation; Uncertainty; Variability; Emissions; Nitrogen oxides;
Development of hourly probabilistic utility NO x emission inventories using time series techniques: Part II—multivariate approach by Amr Abdel-Aziz; H.Christopher Frey (5391-5401).
Inter-unit dependence in the time series of capacity factors was accounted for in developing time series models for predictions of uncertainty in hourly NO x emissions for base load coal-fired power plants. Analyses were conducted for 32 units from 9 plants for a 1995 base case, and 1998 alternate case, and a future scenario in 2007. Multivariate time series models were employed in the analyses to account for the dependence between emissions from correlated units. The trade-off of using this approach is the complexity involved in the modeling process, including selection of model parameters and computational effort in the simulation process. Sufficient simultaneously recorded data for all correlated units must be available for purposes of model development. The results were compared to those of the inter-unit independent approach employed in a companion paper. Inter-unit correlations for capacity factor were as high as 0.86 and for total emissions were as high as 0.62. The total daily inventory for the 1995 case had a 95% confidence interval of 497–705 t/d which represents an uncertainty range of −15% to +20% of the average value of 587 t/d. The 2007 case had an uncertainty range of −8% to +15%. These uncertainty ranges are wider than the corresponding ranges obtained from the inter-unit independent approach. Simulations from the vector autoregressive time series approach that accounted for inter-unit correlation in capacity factor were more accurate than the inter-unit independent approach when compared to observed data.
Keywords: Autocorrelation; Uncertainty; Variability; Emissions; Nitrogen oxides;
Size distribution of acidic sulfate ions in fine ambient particulate matter and assessment of source region effect by Y Hazi; M.S.A Heikkinen; B.S Cohen (5403-5413).
Human exposure studies strongly suggested that the fine fraction of ambient particulate matter (PM) and its associated acidic sulfates are closely correlated with observed adverse health effects. Acidic sulfates are the products of atmospheric sulfur dioxide oxidation and neutralization processes.Few data are available on the amount and size distribution of acidic sulfates within the fine fraction of ambient PM. Knowledge of this distribution will help to understand their toxic mechanisms in the human respiratory tract.The goals of this research were: (1) to measure the size distribution of hydrogen ion, sulfate, and ammonium within the fine fraction of the ambient aerosol in air masses originating from different source regions; and (2) to examine the effect of the source region and the seasons on the sampled PM composition.Six size fractions within the fine ambient PM were collected using a micro-orifice impactor. Results from 30 sampling sessions demonstrated that higher total concentrations of these three ions were observed during the warm months than during the cold months of the year. Size distribution results show that the midpoint diameter of the fraction of particles with the largest fraction of hydrogen, sulfate and ammonium ions was 0.38 μm. Although most of the mass containing hydrogen and sulfate ions was measured in the fraction of particles with 0.38 μm midpoint diameter, the ultrafine fraction (<0.1 μm) was found to be more acidic. Ambient ion concentrations varied between sampling sessions and seasons, but the overall size distribution profiles are similar.Air mass back trajectories were used to identify the source region of the sampled aerosols. No apparent source region effect was observed in terms of the distribution profile of the ions. However, samples collected from air masses that originated from, or passed over, high sulfur dioxide emission areas demonstrated higher concentrations of the different ions.
Keywords: Acidic sulfate ions; Particle size distribution; Ultrafine particles; Sulfur dioxide oxidation; Air mass back trajectory;
Incineration of different types of medical wastes: emission factors for gaseous emissions by M.C.M. Alvim-Ferraz; S.A.V. Afonso (5415-5422).
Previous research works showed that to protect public health, the hospital incinerators should be provided with air pollution control devices. As most hospital incinerators do not possess such equipment, efficient methodologies should be developed to evaluate the safety of incineration procedure. Emission factors (EF) can be used for an easy estimation of legal parameters. Nevertheless, the actual knowledge is yet very scarce, mainly because EF previously published do not include enough information about the incinerated waste composition, besides considering many different waste classifications. This paper reports the first EF estimated for CO, SO2, NO x and HCl, associated to the incineration of medical waste, segregated in different types according to the classification of the Portuguese legislation. The results showed that those EF are strongly influenced by incinerated waste composition, directly affected by incinerated waste type, waste classification, segregation practice and management methodology. The correspondence between different waste classifications was analysed comparing the estimated EF with the sole results previously published for specific waste types, being observed that the correspondence is not always possible. The legal limit for pollutant concentrations could be obeyed for NO x , but concentrations were higher than the limit for CO (11–24 times), SO2 (2–5 times), and HCl (9–200 times), confirming that air pollution control devices must be used to protect human health. The small heating value of medical wastes with compulsory incineration implied the requirement of a bigger amount of auxiliary fuel for their incineration, which affects the emitted amounts of CO, NO x and SO2 (28, 20 and practically 100% of the respective values were related with fuel combustion). Nevertheless, the incineration of those wastes lead to the smallest amount of emitted pollutants, the emitted amount of SO2 and NO x reducing to 93% and the emitted amount of CO and HCl to more than 99%.
Keywords: Medical waste incinerator; Legal limits; Waste classification; Waste segregation; Emission rates;
Present scenario of air quality in Delhi: a case study of CNG implementation by P. Goyal; Sidhartha (5423-5431).
The present study discusses the ambient air quality of Delhi from the point of view of change of diesel by Compressed Natural Gas (CNG) in transportation in Delhi. Several initiatives were taken to reduce extremely high levels of pollutants present in the ambient air of urban city. One of the initiatives was to move public transport to CNG, which has been implemented in Delhi since April 2001. Delhi boasted CNG in nearly 2200 buses, 25,000 three wheelers, 6000 taxis and 10,000 cars. However, more than half of the vehicles are yet to be changed to CNG.A relative comparison of ambient air concentration of pollutants, e.g. carbon monoxide (CO), sulphur dioxide (SO2), suspended particulate matter (SPM) and oxides of nitrogen (NO X ), emitted from transport sector, during the years 1995–2000 (without CNG) and the year 2001 (with CNG) has been made in order to assess the impact of CNG vehicles on ambient air quality in Delhi. It has been found that concentration contribution of above pollutants has been reduced considerably.The annual average concentration of SPM came down to 347 from 405 μg m−3, which is still beyond the permissible limits. The concentration of annual averages of CO, SO2 and NO X decreased to 4197 from 4681 μg m−3, 14 from 18 μg m−3 and 34 from 36 μg m−3, respectively, and are well within the permissible limits. An analysis of SO2/NO X and CO/NO X concentrations, whose correlation coefficient r 2 has the values 0.7613 and 0.7903, respectively, indicates that point sources are contributing to SO2 and mobile sources are contributing to NO X concentrations.
Keywords: CNG; Diesel; Public transport; Air pollution; Vehicles;
Confined catalytic oxidation of volatile organic compounds by transition metal containing zeolites and ionizer by Teresa S.C Law; Christopher Chao; George Y.W Chan; Anthony K.Y Law (5433-5437).
Ion exchange of zeolite, NaX, at different concentrations of cobalt (II) solutions can play an important role in gaseous contaminant destruction. The performance of the resulting zeolites on acetone removal when working together with an ionizer was evaluated. It was found that the cobalt containing zeolites worked better than the original NaX in our experiments. Catalytic oxidation mechanism of the volatile organic compounds (VOCs) inside the pores of zeolite was proposed. It is believed that the octahedral coordinated cobalt (II) complexes shift to tetrahedral coordination upon entering into the pores of NaX, which then work with the reactive oxygen species released from the ionizer and catalyze the oxidation reactions of the adsorbed VOCs. The results have shown potential applications in odor removal and indoor air quality control.
Keywords: Catalytic oxidation; Zeolite; Transition metals; Volatile Organic Compounds;
Instantaneous secondary organic aerosol yields and their comparison with overall aerosol yields for aromatic and biogenic hydrocarbons by Weimin Jiang (5439-5444).
An instantaneous secondary organic aerosol yield (IAY) is a different quantity than an overall aerosol yield (OAY), both qualitatively and quantitatively. Starting from Odum's OAY equation, this paper derives and presents a new equation for the calculation of IAY values. As examples, the two-product form of the equation is applied to 10 representative aromatic and biogenic reactive organic gas (ROG) experiments in the literature. Values of IAY and OAY corresponding to wide ranges of organic aerosol mass concentrations (M 0) are calculated using the new IAY equation in this paper and the original Odum's OAY equation. These IAY and OAY values are shown through aerosol yield curves, which are the plots of IAY or OAY versus M 0. Comparative analysis of the IAY and OAY curves shows that both IAY and OAY increase monotonically with M 0 and they approach a common maximum value when M 0 becomes very high. However, when M 0 approaches zero, OAY also approaches zero but IAY approaches a fixed positive value for a given ROG. At any given M 0 value, the value of IAY is always higher than that of OAY. The relative differences between IAY and OAY are especially significant under typical ambient and experimental M 0 levels. IAY values can be orders of magnitude higher than OAY values and are much better representations of aerosol yields under these M 0 levels. When it is used for secondary organic aerosols (SOA) estimation and modelling, the new IAY equation will significantly improve the underestimation of SOA formation caused by directly using the original OAY equation. More sophisticated SOA algorithms could also be developed based on the IAY equation presented here.
Keywords: Aerosol yield; Secondary organic aerosols; Particulate matter; Reactive organic gas; Air quality modelling;
Lichens as biomonitors of uranium and other trace elements in an area of Kosovo heavily shelled with depleted uranium rounds by Luigi A. Di Lella; Luisa Frati; Stefano Loppi; Giuseppe Protano; Francesco Riccobono (5445-5449).
This paper reports the results of a study using lichens as biomonitors to investigate the small-scale environmental distribution of uranium and other trace elements in an area of Kosovo (Djakovica) heavily shelled with depleted uranium (DU) anti-tank ammunition. The results of total uranium concentrations showed great variability and species-specific differences, mainly due to differences in the exposed surface area of the lichens. The uranium concentrations in lichen samples were rather similar at a site heavily shelled with DU ammunition and at a control site. Unexpectedly, the highest uranium concentrations were found at the control site. The observed U distribution can be explained by contamination of lichen thalli by soil particles. The soil geochemistry was similar at the two sampling sites. The 235 U/238 U ratios in the soil samples suggested a modest DU contribution only at the heavily shelled site. Measurements of U isotopes in lichens did not reveal DU pollution at the control site. The U isotopic ratios in lichens at the shelled site showed variable figures; only two samples were clearly contaminated by DU. There were no signs of contamination by other trace elements.
Keywords: Biomonitoring; Kosovo; Lichens; Uranium; Trace elements;