Atmospheric Environment (v.37, #15)

Health risk assessment of kerosene usage in an informal settlement in Durban, South Africa by E Muller; R.D Diab; M Binedell; R Hounsome (2015-2022).
In Durban, South Africa studies have shown that more than seven out of ten households in low-income metropolitan areas rely on kerosene for domestic purposes, leading to widespread problems of poor indoor air quality. In light of the known health effects of kerosene usage, this study aimed to quantify the health risk for people living in a densely populated informal settlement known as Cato Crest within the Durban metropolitan area. The pollutants investigated included nitrogen dioxide, benzene and toluene. Nitrogen dioxide is known to affect both respiratory and immune systems, benzene is carcinogenic while toluene has a neurological health end point. All three pollutants are harmful when inhaled. The United States Environmental Protection Agency (US EPA) health risk assessment (HRA) framework was applied. Information on the exposure patterns of residents in Cato Crest were acquired through questionnaires in which data on fuel use, building structure, cooking habits and time-activity patterns were collected. Air quality monitoring of nitrogen dioxide and volatile organic compounds was also conducted in the households. The time-activity pattern survey revealed that the exposure periods of individuals in Cato Crest were far greater than the default exposure periods used by the US EPA. The results of the HRA showed that the residents of Cato Crest may experience significant health risks as a result of kerosene usage in their homes. Exposure to 1-h nitrogen dioxide concentration is not likely to produce adverse health effects, whereas exposure over a 24-h period indicates a potential health risk to sensitive individuals in two of the households when US EPA exposure values are used and in all of the households when locally derived exposure values are used. Benzene poses a health risk to sensitive individuals in 50% of the households when local exposure parameters are used, whereas there is no health risk associated with exposure to toluene.
Keywords: Health risk assessment; Kerosene; Time-activity patterns; South Africa; Indoor air quality;

Model simulation of ultrafine particles inside a road tunnel by L. Gidhagen; C. Johansson; J. Ström; A. Kristensson; E. Swietlicki; L. Pirjola; H.-C. Hansson (2023-2036).
A monodispersive aerosol dynamic model, coupled to a 3D hydrodynamical grid model, has been used to study the dynamics of ultrafine particles inside a road tunnel in Stockholm, Sweden. The model results were compared to measured data of particle number concentrations, traffic intensity and tunnel ventilation rate. Coagulation and depositional losses to the tunnel walls were shown to be important processes during traffic peak hours, together contributing to losses of 77% of the particles smaller than 10 nm and 41% of the particles of size 10–29 nm. Particle growth due to water uptake or the presence of a micron-sized, resuspended particle fraction did not have any significant effect on the number of particles lost due to coagulation. Model simulation of particle number concentration response to temporal variations in traffic flow showed that constant emission factors could be used to reproduce the concentration variations of the particles larger than 29 nm, while vehicle-speed-dependent factors are suggested to reproduce the variation of the smallest fractions. The emission factors for particle number concentrations estimated from the model simulation are in general higher and show a larger contribution from light-duty vehicles than what has been reported from a tunnel in California. The model study shows that combined measurements and model simulations in road tunnels can be used to improve the determinations of vehicle emission factors for ultrafine particles under realistic driving conditions.
Keywords: Aerosol model; CFD model; Vehicle emissions; Emission factors; Field experiment;

Spatially averaged flow within obstacle arrays by Tom Bentham; Rex Britter (2037-2043).
Knowledge of the flow velocity within an array of buildings is important in modelling the dispersion of urban air pollution. In this paper a spatially averaged model is derived for U C, the characteristic in-canopy velocity. The model's predictions are compared with experimental results from various sources. The model predicts the in-canopy velocity for a broad range of building packing densities (0.01<λ f<0.44). An alternative form of the model is proposed for sparse arrays (λ f<0.2). A model is also derived for the exchange velocity U E between the in-canopy and above-canopy flows. This model for U E has the correct variation with packing density and gives predictions of the right order but has yet to be directly validated.
Keywords: Pollutant dispersion; Urban flow-field; Building array; Advection velocity; Vertical flux;

Growth of organic aerosols by biogenic semi-volatile carbonyls in the forestal atmosphere by Sou Matsunaga; Michihiro Mochida; Kimitaka Kawamura (2045-2050).
Gas and aerosol samples were collected from 13 to 15 August 2001 in Quercus and Picea mixed forest located at Uryu Experimental Forest of Hokkaido University using an annular denuder air sampling system. Gaseous concentrations of biogenic semi-volatile compounds (glycolaldehyde, hydroxyacetone, n-nonanal and n-decanal) showed a rapid increase in the morning and showed a maximum (61–105 pptv) around noontime. Then their concentrations significantly decreased in the evening, and showed a minimum at mid-night. On the other hand, these compounds in the particulate phase also showed a diurnal variation pattern similar to the gaseous compounds. However, the concentrations continued to increase until the evening and showed the maximum at nearly mid-night. The time lag of several hours in the peak of concentrations of these carbonyls in gas phase and particles indicates a gas-to-particle conversion probably through condensation and adsorption of gaseous compounds onto the pre-existing particles (growth of the aerosols).
Keywords: Oxidation products; Isoprene; Aldehydes; Condensation; Annular denuder; Benzylhydroxyl oxime derivatization;

This study developed a new semi-statistical model based on a Lagrangian approach. The overall effects on the observed pollutant levels at a receptor site were divided into two groups, one including the effects of emissions from various upwind sources and the other including all other effects (including the overall effects of atmospheric dilution, chemical transformation, and wet and dry depositions). The former effects were directly accounted for by a new parameter, an emission factor, defined as the accumulated emission uptake along the air trajectory toward the analyzed receptor site. All other effects were represented by a pollutant transfer coefficient. Meteorological parameters, excluding wind direction, were suggested to simulate this coefficient. The model was used to simulate variations in daily average NO x concentrations at a receptor site in south Taiwan during 1995–1999. Four meteorological factors, temperature, humidity, wind speed and pressure, were used to simulate the pollutant transfer coefficient. The full model successfully explained 61% of the analyzed concentration variations. The emission factor was the single most important factor in the model. When this factor was omitted, the determination coefficient of the model decreased from 61% to 48%. However, the pollutant transfer coefficient still dominated the analyzed variations of concentration.
Keywords: Statistical model; Emission; Regression model; Back trajectories; NO x ;

Characteristics of acid aerosols in the geothermal area of metropolitan Taipei, Taiwan by Mei-Lien Chen; Li-Ting Chen; Yen-Neng Wang; Sheng-Fen Yang; Huei-Chen Chen; I-Fang Mao (2061-2067).
To our knowledge, the characteristics of acid aerosols from sulfur-rich geothermal emissions and human activity have not been reported. This study determines the ambient air concentrations of such chemical components as H2S, SO2, HONO, HNO3, NO2 , NO3 , SO4 2− and H+ in the geothermal area of metropolitan Taipei. Acid aerosols were sampled using a honeycomb denuder/filter pack sampling system (HDS). The highest H2S concentration was 680.7 ppb and the mean was 185.7 ppb at the geothermal sampling site. Very high sulfate concentrations (mean concentration higher than 10 μg m−3) were also observed. The spatial variations are typical of sulfur-containing compounds and H+ aerosols; both have concentrations higher closer to the source of geothermal emissions. The daytime means of acid aerosols are generally higher than the corresponding nighttime values. Geothermal emissions, automobile combustion sources and photochemical reactions are concluded to dominate the characteristics of acid aerosols in the studied area. Direct emissions of SO4 2− and H+ with geothermal steam must be further clarified.
Keywords: Acid aerosol; H2S; Geothermal emission; Photochemical reaction; Spatial variation;

Hygroscopic behavior of atmospheric aerosol in Taipei by Lu-Yen Chen; Fu-Tien Jeng; Chih-Chieh Chen; Ta-Chih Hsiao (2069-2075).
Hygroscopic growth of particles of different sizes and the resultant size distribution changes were observed as a function of the relative humidity (RH). A particle generation device, RH module, and a Tandem Differential Mobility Analyzer system were set up to measure the particle size distributions under different RH conditions. Adopting Nafion as an RH adjusting module, the aerosol hygroscopic observations were successfully performed without the interference caused by blending sample stream with humidified air. The measured deliquescence humidity of model compounds, NaCl and (NH4)2SO4, agree with the theoretical values reported by other investigators. The particle growth factor is enhanced around the RH of 70%. In addition, particle size distribution behaves as two split groups of particles with the RH >76%. The average growth factors of hygroscopic ambient particles in Taiwan are similar to those reported elsewhere. There are several hygroscopic salt compositions in ambient aerosols, (NH4)2SO4 is the most abundant one. Observed particle deliquescence behaviors showed limited alternation of organics on particle growth at higher RH.
Keywords: Hygroscopic growth; TDMA; Aerosol size distribution; Urban aerosol;

Gas and particle phase concentrations of 26 nitro-PAHs were quantified in ambient air collected in downtown Baltimore, MD, an urban region, and in Fort Meade, MD, a suburban area 20 km south-southeast of Baltimore, during January and July 2001. Total (gas+particle) concentrations for individual nitro-PAH compounds varied by as much as five times from sample to sample within each month. 2-Nitrofluoranthene and 9-nitroanthracene were the most abundant of the nitro-PAHs quantitatively analyzed in the air at both sites, accounting for approximately half of the total nitro-PAH concentrations during January and July. Concentrations at Baltimore were on average two to three times higher than those measured at the Fort Meade site. Concentrations for most nitro-PAHs were higher in January than in July, suggesting a reduction in photodecay of nitro-PAHs during January promoted the accumulation of nitro-PAHs. Concentrations of nitro-PAHs produced from gas-phase reactions were significantly correlated with concentrations of oxides of nitrogen (NO x ) measured simultaneously at the Fort Meade site. 3-Nitrophenanthrene and 4-nitrophenanthrene were negatively correlated with NO x and were the only nitro-PAHs correlated with O3, suggesting a different formation mechanism for these compounds compared to the other nitro-PAHs found in this study. The relative contribution of gas-phase reactions and primary emission sources of nitro-PAHs were evaluated using source specific concentration ratios of 2-nitrofluoranthene and 1-nitropyrene (2-NF/1-NP). The mean ratios of 2-NF/1-NP at both sites were statistically higher in July than January, indicating gas-phase reactions were an important source of 2-nitrofluoranthene in the summer. However, in January, gas-phase reactions were reduced, the NO3-initiated reaction in particular, and primary emissions may significantly contribute to ambient nitro-PAH levels. The two dominant gas-phase production pathways of nitro-PAHs from the OH and NO3-initiated reactions were investigated using concentration ratios of 2-nitrofluoranthene and 2-nitropyrene (2-NF/2-NP). At both sites, 2-NF/2-NP ratios indicated that the daytime OH-initiated reaction was the dominant gas-phase formation pathway. The estimated contributions of nitro-PAHs produced through gas-phase reactions via the OH pathway during July were >45% and during January were >83% at both Fort Meade and Baltimore.
Keywords: Nitrated polycyclic aromatic hydrocarbons; Baltimore; Nitro-PAH; PAH; Atmospheric formation;

The relation between NO x emissions and precipitation NO3 in the eastern USA by Thomas J Butler; Gene E Likens; Francoise M Vermeylen; Barbara J.B Stunder (2093-2104).
Changes in total NO x emissions in the eastern USA have been relatively small through the 1990s, even with implementation of the Clean Air Act Amendments of 1990. The decreases in NO x emissions from the non-vehicle sectors have been significantly offset by increases from the vehicle sector.To quantify the impact of NO x emissions on precipitation NO3 , we used a random coefficient model. Regional NO x emission densities were regressed on NO3 concentrations in precipitation from 24 NADP/NTN and NADP/AIRMoN sites for precipitation chemistry in the northeastern and mid-Atlantic regions of the USA. These were areas where changes in NO x emissions have been the greatest. Total NO x , and non-vehicle NO x emissions have declined from 7% to 12% and 19% to 25%, respectively, from 1991 to 2000 in these regions.Different NO x source regions impacting particular sites were evaluated based on 12-, 24- and 36-h air mass back trajectories. A simple random coefficient model based on precipitation NO3 (dependent variable) and total NO x emissions (independent variable) showed a highly significant (P-value<0.0001) relation for the source areas based on 12-h back trajectories. Using this model, a 50% decline in total NO x emissions from the appropriate source regions predicted an overall decline in precipitation NO3 concentration of 38%. A model based on non-vehicle NO x emissions as the independent variable predicted that a 50% decline in non-vehicle emissions, which is a 23% decline in total emissions impacting the area, results in a 19% decline in precipitation NO3 concentration. Similar results are found when source areas based on 24- and 36-h back trajectories are used. The several models evaluated, using the different-sized source regions and either total or non-vehicle NO x emissions, predict that reductions in NO x emissions should reduce NO3 concentrations (and deposition) with an efficiency ranging between 75% and 95%. It can be inferred that equivalent reductions (in terms of μeq l−1) in precipitation acidity will also occur.
Keywords: Nitrogen deposition; Acid deposition; Nitrogen oxide; Acid rain; Precipitation chemistry trends; Precipitation nitrate;

The effects of diesel particulate filters (DPFs) on regulated emissions and organic species were measured for several medium-duty diesel vehicles. Vehicles were measured in three configurations: a baseline California in-use diesel fuel, a low-aromatic, low-sulfur diesel fuel, and a DPF with a low-aromatic, low-sulfur diesel and a more commercial low-sulfur diesel fuel. The organic species measurements included C1–C13 hydrocarbon species, C1–C8 carbonyls, and semi-volatile and PM-based polycyclic aromatic compounds (PACs). Tests on vehicles operating with DPFs showed reductions ranged from 89±2.3% to 98±0.7% for PM, 72±2.5% to 80±0.6% for THC, and 81±1% to 90%±1.3 for CO. Although some fuel effects were observed, they were considerably smaller than those found for the DPFs. Detailed C1–C13 organic gas measurements showed alkenes and carbonyls to be the most prominent compound classes, with formaldehyde, ethene, acetaldehyde, and ethyne having the highest emission rates. Large reductions in alkenes, alkynes, and aromatics were found for the DPF, with smaller reductions also found for alkanes and carbonyls. Total PAC emissions were 4.34, 2.25, and 0.69 mg/mi, respectively, for the baseline fuel, the low-aromatic, low-sulfur diesel fuel and DPF with low-sulfur diesel fuel. The majority of the PACs were found in the semi-volatile phase.

Using ambient concentrations of molecular markers, chemical mass balancing calculations have been performed to estimate the contribution of source categories to ambient fine particle levels at four sites in Houston, TX. Eight source profiles obtained using analytical methods equivalent to the techniques used in analysis of the ambient sample were used for the calculations. The chemical mass balancing model accurately reconstructed the measured concentrations of 24 molecular markers and three fine particle chemical components to estimate the contribution of each source to ambient fine particle loads. The results show that at three sites in the Houston urban area, diesel exhausts contribute between 1.6 and 3.7 μg m−3 to ambient fine particle levels, while at an upwind background site, diesel exhausts represent 0.5 μg m−3 of ambient fine particulate matter. Other important sources include gasoline-powered vehicles (1.1–2.8 μg m−3 at three urban sites and 0.5 μg m−3 at the background site); paved road dusts (1.0–2.8 μg m−3 urban and 0.1 μg m−3 background); meat cooking operations (0.9–1.3 μg m−3 urban and 0.7 μg m−3 background) and wood combustion (0.2–0.3 μg m−3 urban and <0.1 μg m−3 background). At one site located near the highly industrialized Houston Ship Channel, fuel oil combustion contributed an estimated 1.5 μg m−3, while fuel oil combustion was not an important contribution at the other sites. Model runs using seasonally averaged data showed a high variation in source strength between seasons for some sources (i.e. paved road dusts much higher in the spring and summer than in the winter), while other sources showed little or no seasonal variation (i.e. vehicle exhausts and meat cooking operations).
Keywords: PM2.5 source apportionment; Molecular markers; Organic speciation;

Organic aerosol growth by acid-catalyzed heterogeneous reactions of octanal in a flow reactor by Myoseon Jang; Sangdon Lee; Richard M. Kamens (2125-2138).
Octanal was chosen as a model carbonyl compound to study aerosol growth by the heterogeneous acid-catalyzed reactions. The heterogeneous reactions of octanal in the presence/absence of acidified seed aerosols were conducted in a 2 m flow reactor (2.5 cm ID) under darkness in the presence of background seed aerosols. To facilitate hemiacetal/acetal formation via the acid-catalyzed heterogeneous reaction of octanal, 1-nonanol was also co-injected with inorganic seed aerosols into the flow reactor system.The aerosol population was measured from a series of sampling ports down the flow reactor as a function of distance using a scanning mobility particle sizer (SMPS). These results were used to predict the apparent rate constants for heterogeneous reactions of octanal, optimizing experimentally observed aerosol growth from condensation and heterogeneous reactions. The aldehyde heterogeneous reactions were accelerated in the presence of an acid catalyst (H2SO4), and led to higher aerosol yields, than when H2SO4 was not present in the seed aerosol. Our results showed that the log of the organic aerosol yield is inversely related to humidity in the presence of an acid-catalyst (R 2=0.98). When aerosols were not catalyzed with an acid, aerosol growth %yields were neither sensitive nor linear with %RH (R 2=0.18). These results may be explained by the fact that acid-catalyzed heterogeneous reactions of aldehydes are significantly accelerated as the acidity increases.The SMPS was also operated in two different aerosol-sampling flow rates to characterize particle off-gassing while particles were inside the SMPS. The off-gassing of organic compounds from the particle phase was smaller with an acid catalyst than without an acid catalyst. Fourier transform infrared spectrometry (FTIR) was employed to demonstrate the direct transformation of chemical functional groups by acid-catalyzing the reactions of octanal with 1-nonanol as a thin liquid layer on a zinc selenide (ZnSe) FTIR disk. It was concluded that carbonyls, which are produced by atmospheric photochemical oxidation reactions, can significantly contribute to secondary organic aerosol formation through acid-catalyzed heterogeneous reactions.
Keywords: Aldehydes; Acetal formation; Heterogeneous reaction; Acid catalyst; Humidity effects;

Emissions of trace gases and particles from two ships in the southern Atlantic Ocean by Parikhit Sinha; Peter V Hobbs; Robert J Yokelson; Ted J Christian; Thomas W Kirchstetter; Roelof Bruintjes (2139-2148).
Measurements were made of the emissions of particles and gases from two diesel-powered ships in the southern Atlantic Ocean off the coast of Namibia. The measurements are used to derive emission factors from ships of three species not reported previously, namely, black carbon, accumulation-mode particles, and cloud condensation nuclei (CCN), as well as for carbon dioxide, carbon monoxide (CO), methane (CH4), non-methane hydrocarbons, sulfur dioxide (SO2), nitrogen oxides (NO x ), and condensation nuclei. The effects of fuel grade and engine power on ship emissions are discussed. The emission factors are combined with fuel usage data to obtain estimates of global annual emissions of various particles and gases from ocean-going ships. Global emissions of black carbon, accumulation-mode particles, and CCN from ocean-going ships are estimated to be 19–26 Gg yr−1, (4.4–6.1)×1026  particles yr−1, and (1.0–1.5)×1026  particles yr−1, respectively. Black carbon emissions from ocean-going ships are ∼0.2% of total anthropogenic emissions. Emissions of NO x and SO2 from ocean-going ships are ∼10–14% and ∼3–4%, respectively, of the total emissions of these species from the burning of fossil fuels, and ∼40% and ∼70%, respectively, of the total emissions of these species from the burning of biomass. Global annual emissions of CO and CH4 from ocean-going ships are ∼2% and ∼2–5%, respectively, of natural oceanic emissions of these species.
Keywords: Ship emissions; Particles from ships; Gases from ships; Emissions from ships; Pollution from ships;

The CALMET meteorological model and its puff dispersion model CALPUFF were used to predict dispersion of the sulfur dioxide emissions from industrial and domestic heating sources in Izmir, the third biggest province in Turkey. The modeling domain covered an area of 80×100 km centered at the metropolitan area of Izmir with grid spacing of 1000 m. Statistical analyses were carried out to evaluate the model performance by comparing the predicted and measured time series of sulfur dioxide concentrations at four monitoring stations using two main methods: root of the mean square error (RMSE) and an index of agreement (d). The index of agreement varied from 0.51 to 0.77 at four monitoring stations and the total RMSE ranged from 0.36 to 0.66 for the year 2000. The overall model performance for four monitoring stations was found good with an accuracy of about 68%. The agreement of model predictions and measurements was better for two urban monitoring stations (Karsiyaka and Bornova), compared with the other urban stations (Alsancak and Konak).
Keywords: Air quality modeling; Dispersion model; Air quality monitoring network; Statistical analysis, Emission inventory;