Atmospheric Environment (v.42, #39)

Experiments were conducted on a four-cylinder direct-injection diesel engine using ultralow-sulfur diesel as the main fuel, ethanol as the oxygenate additive and dodecanol as the solvent, to investigate the regulated and unregulated emissions of the engine under five engine loads at an engine speed of 1800 rev min−1. Blended fuels containing 6.1%, 12.2%, 18.2% and 24.2% by volume of ethanol, corresponding to 2%, 4%, 6% and 8% by mass of oxygen in the blended fuel, were used.The results indicate that with an increase in ethanol in the fuel, the brake specific fuel consumption becomes higher while there is little change in the brake thermal efficiency. Regarding the regulated emissions, HC and CO increase significantly at low engine load but might decrease at high engine load, NO x emission slightly decreases at low engine load but slightly increases at high engine load, while particulate mass decreases significantly at high engine load. For the unregulated gaseous emissions, unburned ethanol and acetaldehyde increase but formaldehyde, ethene, ethyne, 1,3-butadiene and BTX (benzene, toluene and xylene) in general decrease, especially at high engine load. A diesel oxidation catalyst (DOC) is found to reduce significantly most of the pollutants, including the air toxics.
Keywords: Ethanol; Ultralow-sulfur diesel; Diesel Engine; Regulated emissions; Unregulated emissions;

Chemical characteristics of fine particles emitted from different gas cooking methods by Siao Wei See; Rajasekhar Balasubramanian (8852-8862).
Gas cooking is an important indoor source of fine particles (PM2.5). The chemical characteristics of PM2.5 emitted from different cooking methods, namely, steaming, boiling, stir-frying, pan-frying and deep-frying were investigated in a domestic kitchen. Controlled experiments were conducted to measure the mass concentration of PM2.5 and its chemical constituents (elemental carbon (EC), organic carbon (OC), polycyclic aromatic hydrocarbons (PAHs), metals and ions) arising from these five cooking methods. To investigate the difference in particle properties of different cooking emissions, the amount and type of food, and the heat setting on the gas stove were kept constant during the entire course of the experiments. Results showed that deep-frying gave rise to the largest amount of PM2.5 and most chemical components, followed by pan-frying, stir-frying, boiling, and steaming. Oil-based cooking methods released more organic pollutants (OC, PAHs, and organic ions) and metals, while water-based cooking methods accounted for more water-soluble (WS) ions. Their source profiles are also presented and discussed.
Keywords: Cooking; Natural gas; Fine particles; Organic acids; Indoor air quality;

Particulate matter, CO and NO as well as 16 polycyclic aromatic hydrocarbons (PAHs) in both gaseous and particulate phases were measured in the stack of a woodchip-fired 50 kW boiler used for domestic heating. The concentrations of ΣPAHs in both gas and particle phases varied from 1.3 to 1631.7 μg m−3. Mean CO and NO concentrations varied from 96 to 6002 ppm and from 28 to 359 ppm, respectively. The effects of fuel parameters (moisture content (MC) and tree species) and boiler operating conditions on pollutant concentrations were investigated. A relationship was established between ΣPAHs in gaseous and particulate phases and CO concentrations. The species of tree used for woodchip was less important than MC and boiler operating conditions in affecting pollutant concentrations. It is recommended that in order to minimise PAH release woodchip fuel should have a low MC, and the boiler should be operated with a load demand (high/moderate heat requirement). Slumber modes when the boiler has no load demand and is effectively a smouldering flame should be avoided. This can be achieved by increasing automatic operation capability of wood-fired boilers, for example, by automatically varying fire rates and having auto-start capabilities. The PAH data obtained from this study is particularly useful in contributing to emissions inventories, modelling, and predictions of ambient air quality.
Keywords: Polycyclic aromatic hydrocarbons; Biomass boiler; Biomass fuels; Combustion; Particulate matter; Moisture content;

Quantification of Saharan and local dust impact in an arid Mediterranean area by the positive matrix factorization (PMF) technique by Jose Nicolás; Massimo Chiari; Javier Crespo; Isabel Garcia Orellana; Franco Lucarelli; Silvia Nava; Carlos Pastor; Eduardo Yubero (8872-8882).
Particle composition data for PM10 samples collected at an urban background location in Elche in southeastern Spain from December 2004 to November 2005 were analysed to provide source identification and apportionment. A total of 120 samples were collected and analysed by Particle Induced X-ray Emission (PIXE) and ion chromatography. Positive matrix factorization (PMF) was used to estimate sources profiles and their mass contributions. The PMF modelling identified six sources: PM10 mass was apportioned to secondary nitrate (26%), secondary sulphate (22%), local soil dust (21%), traffic (13%), sea-salt (11%) and African dust (7%). It is worth noting that PMF was able to identify a Saharan dust source even in the presence of a weighty local dust source, and to quantitatively estimate the contributions of these two sources. The African dust contribution varies, depending on the intrusion days, within a range of 5–40% of the total PM10 concentration. Without the contribution of Saharan dust, 50% of the total exceedances of the PM10 50 μg m−3 EC limit during the studied period would not have taken place.
Keywords: Atmospheric aerosol; Saharan dust; PM10; PIXE; PMF;

The Henry's law constant (K H) of perfluorooctanoic acid (PFOA, C7F15C(O)OH) was determined at 298 K in aqueous sulfuric acid solutions and in aqueous sodium chloride and sulfuric acid mixtures by an inert-gas stripping method in which a helical plate was used to increase the residence time of the gas bubbles in the solutions. The partial pressures of C7F15C(O)OH in the purge gas (P PFOA) were determined by means of Fourier-transform infrared spectroscopy. Time-courses of P PFOA and concentrations of PFOA in the test solutions (C PFOA) differed from those typically obtained by an inert-gas stripping, indicating both the presence of C7F15C(O)OH aggregates, even at low concentrations of C7F15C(O)OH in aqueous sulfuric acid solutions, and the adsorption of gaseous C7F15C(O)OH on the walls of the experimental apparatus. We derived overall gas-to-water partition coefficients (K H′) by simulating the time-courses of P PFOA and C PFOA simultaneously to optimize parameters of the model relating to the partitioning, the aggregation, and the adsorption. The K H′ value for 0.31 mol dm−3 sulfuric acid solutions at 298 K was determined at 3.8 ± 0.1 mol dm−3  atm−1. From the relationship between K H′ and the ionic strength of aqueous sulfuric acid solutions, the K H values of C7F15C(O)OH at 298 K were determined at 9.9 ± 1.5 mol dm−3  atm−1 for pK a  = 2.8 and 5.0 ± 0.2 mol dm−3  atm−1 for pK a  = 1.3. The pK a value of 1.3 seems to be most probable among the reported three values for C7F15C(O)OH, taking into account dependence of K H′ on sulfuric acid concentrations for aqueous sodium chloride and sulfuric acid mixtures. Despite the low pK a value, the relatively small K H of C7F15C(O)OH obtained at 298 K suggests a substantial partitioning of C7F15C(O)OH in air in the environment.
Keywords: Perfluorocarboxylic acids; Column stripping method; Gas-to-water partition; Salting-out effect; Global transport process;

Deposition of fine particles on building internal surfaces by S. El Hamdani; K. Limam; M.O. Abadie; A. Bendou (8893-8901).
The present experimental study aims to measure the deposition of fine particles on building internal surface coverings. A 125-liter experimental chamber has been built in order to evaluate the loss-rate coefficients of 0.35, 0.53, 0.7, 1 and 2 μm particles on eight coverings commonly found in buildings (two sheet vinyl, two wallpapers, two woods, one custom- made plaster and one custom- made concrete) under three airflow intensity levels. Results show that, if particle deposition clearly increases with near-wall airflow velocity, the role of the surface three-dimensional roughness is less evident because of the complex topography of real coverings.
Keywords: Deposition; Particle; Surface covering; Indoor pollution;

A novel approach to investigating indoor/outdoor pollution links: Combined magnetic and PAH measurements by C.J. Halsall; B.A. Maher; V.V. Karloukovski; P. Shah; S.J. Watkins (8902-8909).
In a preliminary study, paired indoor and outdoor air sampling was conducted at three locations around the city of Lancaster, UK to examine the influence of combustion sources on air quality by measuring particulate concentrations, particulate magnetic properties and polyaromatic hydrocarbons (PAHs). With one exception (an indoor suburban air sample), outdoor air samples had higher total suspended particulates (TSP), particle-bound PAH concentrations and magnetic remanence (IRM) values. IRM values were highest for the week-day, outdoor city centre samples and then declined in the sequence: Sunday, city centre > suburban/residential > Lancaster University campus. These data indicate traffic as the major particle-bound PAH, particulates and magnetic source, particularly as sampling was conducted during July in the absence of any space heating. The indoor air samples revealed a wide variation in pollutant concentrations, characterised by higher vapour levels of 2–3 ring PAHs, variable TSP concentrations and variable but generally low IRMs. The differences in PAH concentrations, TSP and IRMs between outdoor and indoor environments indicate limited ingress of outdoor air pollutants to the indoor environment in this study. Our combined PAH and magnetic data identify specific and distinctive indoor pollution signals for each of our sampled sites, reflecting distinct sources. One site, the suburban house, has anomalously high IRM, TSP and particle-bound PAHs. A possible source for these is a cast-iron, wood-burning stove (even though not lit). The city centre indoor site is characterised by high TSP and very low IRMs but high values of the magnetic ratio of anhysteretic remanence:saturation remanence, indicative of ultrafine (sub-micrometre) magnetic grain sizes. The source for this city centre indoor signature is unidentified but may reflect the occupant smoking and/or lighting candles. The indoor campus sample was affected by loss-on-ignition procedures carried out in a teaching laboratory. The combined PAH and magnetic analyses thus provide a sensitive and discriminatory means of identifying outdoor, traffic-derived pollution, and of discriminating between different types of indoor pollution.
Keywords: Pollution; Particulate; PAHs; Magnetic discrimination;

In May 2003, intense forest fires occurred over Siberia, which were the largest fires in the past decade. In order to quantify the effects of these fires on regional air quality in East Asia, we used a global chemical transport model (CTM) with a biomass burning emission inventory constrained by satellite. Our focus was mainly on the enhancements of the ozone and aerosol concentrations due to these fires over East Asia. We first evaluated the model extensively by comparing the simulated and the observed ozone and aerosol concentrations at the EANET sites and found that the simulation reproduced the observed variability of those species. However, some discrepancies were found in the model when compared with the MODIS AOD observations. We tested the sensitivity of the model AOD to different injection heights of fire emissions and found that the model with an injection height of 4.5 km was in better agreement with the observations. We then used our model results to quantify the influences of Siberian forest fires on ozone and aerosols concentrations which were computed using the differences between the simulations with and without Siberian forest fire emissions. The peak increases in the surface PM10 and ozone concentrations were up to 90 μg m−3 and 33 ppbv, respectively, over Siberia. In the downwind regions, the increases ranged from 5 to 30 μg m−3 and from 3 to 20 ppbv for PM10 and ozone concentrations, respectively, having an important implication for air quality over East Asia. Finally, we computed the radiative forcing of aerosols and ozone from the Siberian forest fires as a measure of climate impact. Siberian forest fires were found to act mainly as a cooling agent resulting in a negative radiative forcing of −5.8 W m−2 at the surface over East Asia. The value at the TOA was −1.5 W m−2, indicating that a considerable absorption of radiation occurred in the atmosphere. This result implies that the Siberian forest fires may affect the regional climate over East Asia by intensifying atmospheric stability.
Keywords: Chemical transport model; Biomass burning; Forest fire aerosols; Radiative forcing; Tropospheric ozone;

Impacts of sulfur dioxide from Miyakejima on precipitation chemistry in Japan by Kyo Kitayama; Takashi Simizu; Hiroshi Hara (8923-8933).
Precipitation chemistry data of Japanese Acid Deposition Survey (JADS) by Japan Ministry of the Environment was analyzed to evaluate the influence of SO2 emitted from the volcano of Miyakejima located in the Pacific Ocean 200 km south of Tokyo. Precipitation samples were collected with wet-only samplers on a daily basis at eight sites over Japan. The sampling periods (1997–2005) were divided into three periods in consideration of the start of the eruption, August 2000: 1997–1999 (Period A), 2000–2002 (Period B), 2003–2005 (Period C). The influence was evaluated in terms of the ratio before-to-after the eruption, B/A and C/A. The B/A ratios for mean nss-SO4 2− concentration ranged from 1.1 to 2.3. The average pH decreased at most sites in Period B. The ratios for annual deposition were the same level as those of the concentration. The influence was also assessed for daily concentration and deposition at Tanzawa and Tsukuba, the two closest sites to Miyakejima. The cumulative frequency distributions of the daily nss-SO4 2− concentration shifted to higher concentration for both sites in Period B. Daily pH cumulative frequency distributions shifted to lower values at both sites in Period B. The monthly fraction, nss-SO4 2−/(nss-SO4 2−  + NO3 ), increased immediately after the eruption onset. The eruption was found to have influenced concentrations and deposition of nss-SO4 2− and pH on a national scale, and the sites closest to Miyakejima showed the largest influence.
Keywords: Miyakejima; Precipitation chemistry; Volcano; Sulfate; Japan;

We report on a 1-year continuous precipitation sampling record from an alpine site and a rural site in the Urumqi River Valley, East Tien Shan, China. The 128 samples, collected from April 2003 to February 2004, at two sites were analyzed for the major inorganic ions, pH, electrical conductivity and insoluble microparticles. The precipitation was typically alkaline with a volume-weighted mean pH of 6.99 and 7.27 at the alpine site and the rural site, respectively. Ca2+ was the dominant cation, and SO4 2− was the dominant anion. The precipitation chemistry in this region was mainly controlled by regional Asian dust storms, local dust and anthropogenic activities. The relative impact of anthropogenic activities, specifically uncontrolled coal combustion, was larger at the rural site compared to the alpine monitoring site.
Keywords: Precipitation chemistry; Seasonal variability; Deposition fluxes; Urumqi River Valley;

First continuous measurements of CO2 mixing ratio in central London using a compact diffusion probe by Matthew Rigby; Ralf Toumi; Rebecca Fisher; David Lowry; Euan G. Nisbet (8943-8953).
We present one year of data from the first continuous measurements of carbon dioxide mixing ratio in central London. Measurements were made at an 87 m tower site using the new Vaisala CARBOCAP GMP343 instrument, which was found to provide a compact and inexpensive method for mixing ratio monitoring, in an environment where conventional CO2 sensors could not be accommodated. Measurements were compared with a monitoring site outside London, showing that the city's CO2 “dome” was an order of magnitude smaller than measured at lower levels in other cities. During the night time in the summer, the mixing ratio in central London was found to be significantly lower than at the rural site. This was thought to be explained by the proximity of biogenic sources to the rural sensor, differences between urban and rural mixing heights and/or the interception of a vertical mixing ratio gradient at two different measurement heights. Estimation of the CO2 loading of the air entering the city therefore proved problematic during the summer. As a result, we propose that monitoring of CO2 emission rate using this type of measurement may only be possible in the winter when the influence of these factors is minimal.
Keywords: Urban; Pollution; Boundary layer; Flux;

A comprehensive air quality modeling project was carried out to simulate size and composition resolved airborne particulate matter concentrations in northern and central California using the pollutant concentration and meteorological data collected during the California Regional PM10/PM2.5 Air Quality Study (CRPAQS) from December 15, 2000 to January 7, 2001. Measured 24-h average PM2.5 concentrations during this time period exceeded 180 μg m−3 at Bakersfield, making it the most severe PM2.5 air quality episode ever recorded in the United States with a rigorous measurement database to support modeling. In this paper, the UCD/CIT source-oriented air quality model is used to predict the concentrations of O3, NO, NO2, CO, elemental carbon (EC), organic compounds (OC), nitrate and PM2.5 mass concentration over a 24-day period using a horizontal resolution of 4 km × 4 km to cover all of central California. This is the first extensive evaluation of an air quality model in central California using the fine spatial resolution appropriate for the mountain–valley topography of the region combined with the relatively long multi-week time scales associated with winter stagnation events.Fractional bias (FB) values were calculated at all sites on each day of the study to quantify model performance. The CO (FB = −0.5 to +0.3), O3 (FB = −0.5 to +0.25), NO (FB = −0.9 to −0.1) and NO2 (FB = 0 to +0.4) concentrations predicted by the UCD/CIT model are in general agreement with observations at most monitoring stations throughout the Valley. The predicted PM2.5 concentrations (FB = −0.5 to +0.75) generally agree with observations at Bethel Island, Sacramento, Fresno and Bakersfield spanning the entire length of the model domain. PM2.5 concentrations are over-predicted at the remote monitoring site Angiola in the central portion of the domain. Part of the over-prediction is due to excess fugitive dust emissions. CO, NO, EC and OC were all under-predicted at Angiola, indicating possible missing combustion sources in the emission inventory. The regional nitrate (FB = −1.5 to +1.25) formation dynamics were correctly reproduced by the model simulation but imperfect wind fields cause differences between the predicted vs. measured spatial distribution of nitrate during the last several days of simulation leading to the broader range of fraction bias. Overall, the results of the current study confirm the ability of the air quality model to capture the major features of a severe particulate air pollution event in northern and central California providing a foundation for future studies on source apportionment and emissions control.
Keywords: Source-oriented model; particulate matter; San Joaquin Valley;

A comprehensive air quality modeling project was carried out to simulate regional source contributions to primary airborne particle concentrations in California's central Valley. A 3-week stagnation episode lasting from December 15, 2000 to January 7, 2001, was chosen for study using the air quality and meteorological data collected during the California Regional PM10/PM2.5 Air Quality Study (CRPAQS). The UCD/CIT source oriented air quality model was applied to this episode using both the source-oriented external mixture configuration and an internal mixture with artificial tracers so that source contribution information could be retrieved in less time.The majority of the predicted and measured primary airborne particulate matter mass was composed of elemental carbon (EC) and organic carbon (OC). Previous work has shown that base case EC and OC predictions made by the UCD/CIT model are in good agreement with observations. Model results from the current study show that the highest EC and OC concentrations occur in urban areas and along transportation corridors where primary emissions are largest. Lower concentrations of primary EC and OC are predicted at rural locations in the San Joaquin Valley (SJV).Source contributions predicted by the UCD/CIT air quality model were compared to receptor-oriented source apportionment results produced by the Chemical Mass Balance (CMB) model at Fresno and Angiola. The relative contributions from major sources predicted by the UCD/CIT model agree with the CMB model results, building confidence in the accuracy of the UCD/CIT model predictions at locations where the CMB results are not available. Wood smoke was identified as the major regional source of primary OC in airborne particles in the winter SJV episode, accounting for approximately 50% of the total PM2.5. Diesel engines were also found to be a significant contributor to primary PM2.5 OC and the largest contributor to the predicted PM2.5 EC averaged over a typical day. EC contributions from wood smoke increased at night and sometimes reached as high as 40% of the total PM2.5 EC. The contribution of fugitive dust to primary PM2.5 mass was also predicted to be significant, especially in rural areas, but this result is likely biased high by the lack of an appropriate diurnal profile for dust emissions.The results of the current study suggest that reductions in wood burning and diesel engine activity would reduce the regional concentration of primary PM2.5 during severe winter stagnation events in the SJV.
Keywords: Regional source apportionment; Primary particulate matter; Central California; CRPAQS;