Check out our New Publishers' Select for Free Articles

Atmospheric Environment (v.42, #13)

Editorial board (pp. i).

Atmospheric polycyclic aromatic hydrocarbons: Source attribution, emission factors and regulation by Khaiwal Ravindra; Ranjeet Sokhi; R. René Van Grieken (pp. 2895-2921).

There is an increasing concern about the occurrence of polycyclic aromatic hydrocarbons (PAHs) in the environment as they are ubiquitous in ambient air and some of them are among the strongest known carcinogens. PAHs and their derivatives are produced by the incomplete combustion of organic material arising, partly, from natural combustion such as forest and volcanic eruption, but with the majority due to anthropogenic emissions. The PAH concentration varies significantly in various rural and urban environments and is mainly influenced by vehicular and domestic emissions. The review serves as a database to identify and characterize the emission sources of PAHs and hence various approaches including diagnostic ratio (DR) and principal component analysis (PCA) are discussed in detail. These approaches allow individual PAHs to be associated with their origin sources. The factors that effect PAH emission and estimated emission rate are also discussed in this paper. Although the levels of low molecular weight PAHs are high in vapor phase, most of the probable human carcinogenic PAHs are found to be associated with particulate matter, especially in fine mode particles in ambient air. Many countries have proposed a non-mandatory concentration limit for PAHs, whereas the health risk studies conducted in relation to PAH exposure, urge that these pollutants should be given a high priority when considering air quality management and reduction of impacts.

Keywords: PAH formation; Emission factors; Source apportionment; Air quality standards and regulation

Elemental mercury fluxes over a sub-alpine grassland determined with two micrometeorological methods by J. Fritsche; D. Obrist; M.J. Zeeman; F. Conen; W. Eugster; C. Alewell (pp. 2922-2933).

The exchange of gaseous elemental mercury (GEM) over a sub-alpine grassland in central Switzerland was measured over a full year. Seasonal and diurnal variability were measured with two micrometeorological techniques: the aerodynamic method and the modified Bowen ratio method. With these two methods mean deposition rates of 4.3 and1.7ngm-2h-1 were calculated throughout the vegetation period. As no significant GEM exchange occurred under snow covered conditions the mean annual deposition fluxes reached 2.9 and1.1ngm-2h-1, respectively. A fair weather period in October 2005 was selected to specifically study diurnal patterns of GEM exchange. During this time vertical day-time GEM gradients averaged0.01ngm-4 and night-time gradients0.07ngm-4, but no clear diurnal pattern of the GEM fluxes was observed. The measured gradients were very small, which entailed considerable uncertainties in the calculated GEM fluxes. However, the observed exchange pattern is verified by the agreement of the applied methods regarding the direction of the flux and the pronounced seasonal trends. Complementary measurements of total mercury in precipitation during three rain events revealed that dry deposition of GEM would account for 67% of a total annual input of0.26gha-1 and would therefore constitute a major deposition pathway.

Keywords: Gaseous mercury; Micrometeorology; Aerodynamic method; Modified Bowen ratio; Background soil; Switzerland

Numerical study of the impact of urbanization on the precipitation over Taiwan by C.-Y. Chuan-Yao Lin; W.-C. Chen; Shaw C. Liu; Y. An Liou; G.R. Liu; T.H. Lin (pp. 2934-2947).

A highly developed industry and a large population density have turned the western plain of Taiwan into a mega-suburb with many cities and small towns and countless factories, and roads. As a result, the western plain is experiencing a regional heat-island effect. The MM5 mesoscale model was conducted in order to study and evaluate the impacts of the heat-island effect on regional weather, including thunderstorms, over Taiwan. According to land use data provided by the US Geological Survey (USGS), we assumed three different urban sizes in the simulation study to theoretically evaluate the impact of urbanization on the precipitation.Along with urban size increase in central Taiwan, more pronounced effects of meteorological parameters were shown in the sensitivity experiment with urban cases. For the urban case (case SA, with urban size 15×15km²), sensible heat flux is nearly 500Wm⁻² around noon-time. It is about a factor of 3 more than the non-urban case (case CT) over the western plain. The surface air temperature in case SA increased by nearly 3°C and humidity decreased with nearly 10% more than case CT. Along with the urban size increases in central Taiwan, the effects are the surrounding areas and were more pronounced not only the precipitation over downwind areas. Apparently, the unique and complex topographic features in Taiwan, including the lifting effect of the mountain bordering the western plain, are also play important roles for precipitation formation. Numerical study suggests that the heat-island effect over the western plain could perturb thermal and dynamic processes and hence affect the location of thunderstorms and precipitation over Taiwan's western plain.

Keywords: Urbanization; Simulation; Precipitation; Taiwan

Seasonal trends in vegetation and atmospheric concentrations of PAHs and PBDEs near a sanitary landfill by Annick D. St-Amand; Paul M. Mayer; Jules M. Blais (pp. 2948-2958).

Spruce needle and atmospheric (gaseous and particulate-bound) concentrations were surveyed near a sanitary landfill from February 2004 to June 2005. The influence of several parameters such as temperature, relative humidity, wind speed and direction, as well as increased domestic heating during the winter was assessed. In general, polybrominated diphenyl ethers (PBDE) and polycyclic aromatic hydrocarbons (PAH) concentrations in spruce needles increased over time and decreased following snowmelt with a minimum coinciding with bud burst of deciduous trees. Atmospheric concentrations of PBDE and PAH, both particulate-bound and gaseous phase, were linked to daily weather events and thus showed more variability than those in spruce needles. Highest PAH concentrations were encountered during the winter, likely reflecting increased emission from heating homes. Pseudo Clausius-Clapeyron plots revealed higher PBDE gaseous concentrations with increasing temperature, but showed no correlation between PAH gaseous concentrations and temperature as this effect was obscured by seasonal emission patterns. Finally, air mass back trajectories and local wind directions revealed that particulate-bound PBDEs, along with both gaseous and particulate-bound PAHs were from local sources, whereas gaseous PBDEs were likely from distant sources.

Keywords: PBDE; PAH; Sanitary landfill; Atmospheric; Vegetation; Temperature; Wind

The impacts of anthropogenic emissions on the precipitation chemistry at an elevated site in North-eastern China by Yan Wang; Ka Ming Wai; Jian Gao; Xiaohuan Liu; Tao Wang; Wenxing Wang (pp. 2959-2970).

Ninety precipitation samples were collected from 2004 to 2006 at the summit of the Mt. Tai in order to detect the impacts of regional sources of pollution on precipitation chemistry in the highly polluted North China Plains. The annual volume-weighted pH of the precipitation was found to be 4.7, in contrast to the less-acidic nature (pH>5.6) of precipitation in northern China reported in many past studies. Non-sea-salt (nss)-SO₄²⁻ (131.5μeqL⁻¹), NH₄⁺ (82.2μeqL⁻¹) and Ca²⁺ (61.4μeqL⁻¹) were the most abundant species in precipitation. The wide range of the Cl⁻/Na⁺ ratios (0.2–5.4) in precipitation implied the co-existence of Cl⁻ enrichment and depletion. The nss-SO₄²⁻, NO₃⁻, NH₄⁺, Ca²⁺ and K⁺ concentrations peaked in spring, but with the lowest acidity. The very strong correlations of Ca²⁺ with nss-SO₄²⁻ and NO₃⁻ suggested a significant uptake of nss-SO₄²⁻ and NO₃⁻ on dust aerosol during spring. Samples with the lowest pH value (4.5) are associated with the stagnant air conditions. The nss-SO₄²⁻ and NH₄⁺ concentrations at Mt. Tai were the highest compared with those at the EANET, NADP and EMEP sites of similar elevations. With relatively high rainfall amount measured at our site, the high wet deposition of the major acidic/alkaline species exerted large loadings to the ecosystem. The associated impacts on agriculture, soil and aquatic systems should be investigated.

Keywords: Mt. Tai; Precipitation chemistry; Correlation analysis; Back trajectory analysis

Observation of ozone and carbon monoxide at Cape Hedo, Japan: Seasonal variation and influence of long-range transport by Jeeranut Suthawaree; Shungo Kato; Akinori Takami; Hisayoshi Kadena; Mikiko Toguchi; Kazuo Yogi; Shiro Hatakeyama; Yoshizumi Kajii (pp. 2971-2981).

We performed continuous measurements of O₃ and CO at Cape Hedo (26.8°N, 128.2°E, 60m above sea level), a remote measurement site on Okinawa Island in Japan, in order to investigate the long-range transportation of air pollution from highly polluted regions in East Asia. The O₃ and CO concentrations, from January 2002 to May 2004, show maximum values during the winter–spring period with monthly averaged concentrations of 52 and 280ppbv, and minimum values during the summer period with concentrations of 15 and 81ppbv, respectively. Based on the transport paths identified by calculating 5-day backward trajectory, air masses are categorized into four groups as follows: “C” for China, “K” for Korea, “J” for Japan, and “O” for the Pacific Ocean. The analysis reveals similar fates for the O₃ and CO concentrations for the air masses in the C and K groups, which exhibited the highest monthly averaged concentrations along with high concentrations within the J group where the lowest concentration is found in the O group. Relationship between O₃ and CO concentrations reveals positive correlations in the spring and summer months. This suggests that the enhancements of O₃ during these seasons are likely to be resulted from the photochemical O₃ production in this region.

Keywords: Long-range transport; East Asia; Air pollution; O; ₃; CO

Ambient air pollution and annoyance responses from pregnant women by Sabrina Llop; Ferran Ballester; Marisa Estarlich; Ana Esplugues; Fernandez-Patier Rosalia Fernández-Patier; Ramon Rosa Ramón; Alfredo Marco; Amelia Aguirre; Jordi Sunyer; Iniguez Carmen Iñiguez (pp. 2982-2992).

To describe the degree of annoyance caused by air pollution and noise in pregnant women in a birth cohort; to determine the modifying factors and their relation with exposure to ambient nitrogen dioxide (NO₂).The study population was 855 pregnant women in Valencia, Spain. Annoyance caused by air pollution and noise, and explanatory factors were obtained from 786 pregnant women through a questionnaire. NO₂ levels were determined combining measurements at 93 points within the area of study and using geostatistical techniques (kriging).In all 7.9% of the women reported high annoyance caused by air pollution and 13.1% high annoyance caused by noise. There was a significant difference in the degree of annoyance due to both air pollution and noise depending on the area where the women lived and their working status. The degree of annoyance correlated better with measured NO₂ at the municipality level (air pollution: r=0.53; noise: r=0.44) than at the individual level (air pollution and noise: r=0.21). On multivariate analysis, being a housewife, higher NO₂ levels and high traffic density were associated with higher degrees of annoyance.There was a high percentage of women who perceived medium–high annoyance due to noise and air pollution. Annoyance caused by environmental pollutants could lead to some psychological effects, which impair the quality of life, or even physiological ones, which affect prenatal development.

Keywords: Human reactions; Prenatal development; Noise; Nitrogen dioxide; Nuisance

Temporal patterns of n-alkanes at traffic exposed and suburban sites in Vienna by Kotianova Petra Kotianová; Hans Puxbaum; Heidi Bauer; Alexandre Caseiro; Iain L. Marr; Cík Gabriel Čík (pp. 2993-3005).

Temporal and spatial trends of particulate n-alkanes C₂₄–C₃₃ have been investigated at urban-fringe and traffic exposed inner urban sites of a larger European city. The annual average sum of n-alkanes at the four sampling sites ranged from 21 to 31ngm⁻³. The urban impact factor was ∼30% averaged over the year. The seasonal biogenic emissions of the uneven n-alkanes cause a considerable seasonal variation in the distribution pattern of the alkanes in PM10 both in the city and at the suburban sites. The trends in the distribution pattern can be summarized using the odd carbon preference index CPI_odd and the plant wax number %WNA, both of which show clear maxima in summer pointing to important biogenic sources of n-alkanes. The biogenic contributions to the total n-alkanes were around 9% in winter (DJF), and 37% in summer (JJA) at the urban-fringe sites. At the inner city sites, the urban impact is dominated by n-alkanes from combustion sources at all seasons. A comparison of two approaches to determine the contribution of the “plant debris” source to ambient PM10 indicates two different mechanisms to form atmospheric “plant debris”. The observed relative contributions of plant debris to PM10 are well in the same range but exhibit differences in the seasonal trend. Considering the different underlying concepts, the agreement of the derived plant debris contributions to PM10 is noteworthy.

Keywords: n; -Alkanes; PM10; Particulate matter; Source analysis; Biogenic particles

Characterization of aerosol particles from grass mowing by joint deployment of ToF-AMS and ATOFMS instruments by Frank Drewnick; Manuel Dall’Osto; Roy Harrison (pp. 3006-3017).

During a measurement campaign at a semi-urban/industrial site a grass-cutting event was observed, when the lawn in the immediate surrounding of the measurement site was mowed. Using a wide variety of state-of-the-art aerosol measurement technology allowed a broad characterization of the aerosol generated by the lawn mowing. The instrumentation included two on-line aerosol mass spectrometers: an Aerodyne Time-of-Flight Aerosol Mass Spectrometer (ToF-AMS) and a TSI Aerosol Time-of-Flight Mass Spectrometer (ATOFMS); in addition, a selection of on-line aerosol concentration and size distribution instruments (OPC, APS, SMPS, CPC, FDMS-TEOM, MAAP) was deployed. From comparison of background aerosol measurements during most of the day with the aerosol measured during the lawn mowing, the grass cutting was found to generate mainly two different types of aerosol particles: an intense ultrafine particle mode (1h average: 4μgm⁻³) of almost pure hydrocarbon-like organics and a distinct particle mode in the upper sub-micrometer size range containing particles with potassium and nitrogen-organic compounds. The ultrafine particles are probably lubricating oil particles from the lawn mower exhaust; the larger particles are swirled-up plant debris particles from the mowing process. While these particle types were identified in the data from the two mass spectrometers, the on-line aerosol concentration and size distribution data support these findings. The results presented here show that the combination of quantitative aerosol particle ensemble mass spectrometry (ToF-AMS) and single particle mass spectrometry (ATOFMS) provides much deeper insights into the nature of the aerosol properties than each of the instruments could do alone. Therefore a combined deployment of both types of instruments is strongly recommended.

Keywords: Lawn mowing; Aerosol mass spectrometry; ToF-AMS; ATOFMS

Gas-phase rate coefficients for reactions of NO₃, OH, O₃ and O(³P) with unsaturated alcohols and ethers: Correlations and structure–activity relations (SARs) by Christian Pfrang; Martin D. King; Mareike Braeckevelt; Carlos E. Canosa-Mas; Richard P. Wayne (pp. 3018-3034).

Experimental difficulties sometimes force modellers to use predicted rate coefficients for reactions of oxygenated volatile organic compounds (oVOCs). We examine here methods for making the predictions for reactions of atmospheric initiators of oxidation, NO₃, OH, O₃ and O(³P), with unsaturated alcohols and ethers. Logarithmic correlations are found between measured rate coefficients and calculated orbital energies, and these correlations may be used directly to estimate rate coefficients for compounds where measurements have not been performed. To provide a shortcut that obviates the need to calculate orbital energies, structure–activity relations (SARs) are developed. Our SARs are tested for predictive power against compounds for which experimental rate coefficients exist, and their accuracy is discussed. Estimated atmospheric lifetimes for oVOCs are presented. The SARs for alkenols successfully predict key rate coefficients, and thus can be used to enhance the scope of atmospheric models incorporating detailed chemistry. SARs for the ethers have more limited applicability, but can still be useful in improving tropospheric models.

Keywords: Oxygenated VOCs; Alkenol; Ozone; Hydroxyl; Nitrate; Ether

Secondary organic aerosol formation from the gas phase reaction of hydroxyl radicals with m-, o- and p-cresol by F. Françoise Henry; Cecile Coeur-Tourneur; F. Frédéric Ledoux; Alexandre Tomas; Dominique Menu (pp. 3035-3045).

Secondary organic aerosol (SOA) formation during the atmospheric oxidation of cresols was investigated using a large smog chamber (8000L), at atmospheric pressure, 294±2K and low relative humidity (6–10%). Cresol oxidation was initiated by irradiation of cresol/CH₃ONO/NO/air mixtures. The cresol loss was measured by gas chromatography with a flame ionization detector (GC-FID) and the temporal evolution of the aerosol was monitored using a scanning mobility particle sizer (SMPS). The overall organic aerosol yield ( Y) was determined as the ratio of the suspended aerosol mass corrected for wall losses ( M_o) to the total reacted cresol concentrations assuming a particle density of 1.4gcm⁻³.Analysis of the data clearly show that Y is a strong function of M_o and that SOA formation can be expressed by a one-product gas/particle partitioning absorption model. The aerosol formation is affected by the initial cresol concentration, which leads to aerosol yields from 9% to 42%. These results are in good agreement with a recent study performed on SOA formation from the photo-oxidation of o-cresol in a smog chamber. To our knowledge, the present work represents the first investigation of SOA formation from OH reaction with m- and p-cresol.

Keywords: Cresol isomers; Hydroxyl radical; Secondary organic aerosol yields; Smog chamber

Photochemical formation of peroxides and fluorescence characteristics of the water-soluble fraction of bulk aerosols collected in Okinawa, Japan by Hitomi Nakajima; Kouichirou Okada; Yukiko Kuroki; Yoshihide Nakama; Daishi Handa; Takemitsu Arakaki; Akira Tanahara (pp. 3046-3058).

Photochemical reactions of dissolved organic compounds, fluorescent dissolved organic matter (FDOM) in particular, are implicated as an important source of peroxides, but their contribution to overall peroxide formation is not well understood. We studied the photochemical formation of peroxides (hydrogen peroxide and organic peroxides), together with changes in fluorescent properties of water-soluble fraction (WSF) solutions of bulk aerosols ( n=28) collected in Okinawa, Japan. Monochromatic wavelengths of 313, 334, 366, and 405nm were used to examine the samples, and the changes in peroxide concentrations and fluorescence intensities (FIs) during these illuminations were measured. For many samples, two peaks of fluorescence were found in the WSF solutions at excitation/emission wavelengths (Ex/Em) of 250–275/375–455 and 300–320/400–440nm, which can be signatures for fulvic acid-like compounds. Several samples collected between November and April (winter samples) showed another fluorescence peak at 260–290/305–345nm, which could be due to the presence of aromatic amines. As illumination time increased, the peroxide concentrations increased and the FI changed, but not uniformly. The FI and peroxide photo-production rates were only weakly correlated ( R<0.36), and the correlation between FI and dissolved organic carbon (DOC) concentrations was also weak ( R<0.75). These results suggest that the photochemistry of FDOM may not comprise a dominant pathway to form peroxides in the WSF solutions, but that peroxides are formed as a result of complex processes in the WSF solutions of aerosols collected in Okinawa.

Keywords: Hydrogen peroxide; FDOM; Fluorescence; Bulk aerosols; Okinawa

Size distribution of trace organic species emitted from biomass combustion and meat charbroiling by Michael J. Kleeman; Michael A. Robert; Sarah G. Riddle; Philip M. Fine; Michael D. Hays; James J. Schauer; Michael P. Hannigan (pp. 3059-3075).

Size-resolved particulate matter emissions from pine, California oak, east coast oak, eucalyptus, rice straw, cigarette smoke, and meat cooking were analyzed for trace organic species using solvent-extraction followed by GC–MS analysis. Six particle size fractions were studied between 0.056, 0.1, 0.18, 0.32, 0.56, 1.0, and 1.8μm particle diameter. The smallest particle size fraction analyzed was in the ultrafine (Dp<0.1μm) range that has been implicated as a potential health concern. Fourteen PAHs were detected in the ultrafine size fraction of wood smoke with the most abundant species (benzo[ ghi]fluoranthene) emitted at a rate of 0.2–0.4(mgkg⁻¹ wood burned). Nine PAHs were detected in the ultrafine size fraction of rice straw smoke with the most abundant compound (benzo[ a]pyrene) emitted at 0.01(mgkg⁻¹ rice straw burned). The most abundant PAH measured in the ultrafine size fraction of cigarette smoke was benzo[ ghi]fluoranthene (0.07mgcigarette⁻¹) followed closely by chrysene/triphenylene (0.06mgcigarette⁻¹).Besides PAHs, the most abundant compounds identified in the wood included levoglucosan (−1 burned), acetovanillone (0.06−0.23mgkg⁻¹ burned), coniferylaldehyde (2.7−13.21mgkg⁻¹ burned), iso-eugenol (0.07−0.53mgkg⁻¹ burned), and vanillin (0.12−0.46mgkg⁻¹ burned). The size distribution of each of these compounds was highly correlated ( R²>0.9) with the size distribution of particle-phase organic carbon (OC) and/or elemental carbon (EC). The only organic compounds besides PAHs detected in the ultrafine size fraction of rice straw and cigarette smoke were benz[ de]anthracen-7-one (0.19mgkg⁻¹ rice straw burned) and 4-methylphenylacetone (2.64mgcigarette⁻¹), respectively. Caffeine was measured in cigarette smoke size fractions >0.1μm with a total PM_1.8 emissions rate of 1(mgcigarette⁻¹). The most abundant organic species measured in meat cooking smoke was cholesterol with a size distribution that was highly correlated with both OC and EC. The concentration of each compound normalized by the concentration of total OC was relatively uniform for all particle sizes. Cholesterol and levoglucosan should prove to be useful tracers for meat cooking and wood smoke emissions in the ultrafine size range.

Keywords: Molecular marker; Size distribution; Ultrafine particle source apportionment

Scavenging of soluble gases by evaporating and growing cloud droplets in the presence of aqueous-phase dissociation reaction by Tov Elperin; Andrew Fominykh; Boris Krasovitov (pp. 3076-3086).

In this study we performed numerical analysis of simultaneous heat and mass transfer during evaporation and condensation of a cloud droplet in the presence of soluble gases. It is assumed that gas absorption is accompanied by subsequent aqueous-phase equilibrium dissociation reactions. The system of transient conjugate nonlinear energy and mass conservation equations was solved using anelastic approximation and taking into account thermal effect of gas absorption. It was shown that nonlinear behavior of different parameters, such as temperature and absorbate concentration at the droplet surface stems from the interaction of heat and mass transfer processes. We found that thermal effect of absorption and Stefan flow result in the maximum of droplet surface temperature during the transient period of droplet evaporation. It was shown that heat and mass transfer rates in water droplet–air–water vapor system at short times are considerably enhanced under the effects of Stefan flow, heat of absorption and dissociation reactions within the droplet. Comparison of the results obtained using the model of physical absorption of sulfur dioxide in water droplet with the predictions of the present model that takes into account the subsequent equilibrium dissociation reactions showed that the model of physical absorption underestimates the value of droplet surface temperature and overestimates the average concentration of [SO₂·H₂O] at the transient stage of gas absorption. The performed calculations showed that the value of pH increase with the increasing relative humidity (RH).

Keywords: Heat transfer; Mass transfer; Droplet evaporation; Gas absorption

The impact of urban street canyons on population exposure to traffic-related primary pollutants by Ying Zhou; Jonathan I. Levy (pp. 3087-3098).

The relationship between emissions and population exposures to traffic-related air pollutants is a necessary component of any assessment of mobile source control strategies. In this analysis, part of the New York Metropolitan Exposure to Traffic Study (NYMETS), we simulated atmospheric dispersion and population exposure in densely populated street canyons in mid-town Manhattan. We estimated population exposure using the concept of an intake fraction (iF), defined as the fraction of material released from a source that is eventually inhaled or ingested by a population. We applied the Operational Street Pollution Model (OSPM) for inert pollutants (e.g., CO, PM_2.5), reactive pollutants (e.g., NO and NO₂), and ultrafine particles. Concentrations were linked with different subpopulations, including residents, workers, and pedestrians, incorporating time-activity patterns and differential breathing rates. For the base case scenario, the total iF for a 100-m-long street canyon including the contribution of different subpopulations is on the order of 10⁻³. Daytime office workers and pedestrians contribute most to the overall iF, together contributing over 80% for all pollutants. Univariate sensitivity analyses show that iFs are sensitive to the street configuration and slightly sensitive to traffic volume, speed, and percent of trucks. Our iF estimates are similar in magnitude to those found for indoor environmental tobacco smoke and are substantially higher than previous mobile source estimates, mainly due to the higher population density in street canyons. Our findings emphasize the importance of controlling emissions in urban street canyons, and the need to study high-resolution near-source exposures for primary pollutants in urban settings to inform cost–benefit analyses.

Keywords: Air pollution; Exposure assessment; Intake fraction; Particulate matter; Street canyon; Traffic

Emission factors of PM species based on freeway measurements and comparison with tunnel and dynamometer studies by Zhi Ning; Andrea Polidori; James J. Schauer; Constantinos Sioutas (pp. 3099-3114).

Emission factors of various particle species from light- and heavy-duty vehicles (LDVs and HDVs, respectively), including organic and elemental carbon (OC and EC), sulfate, polycyclic aromatic hydrocarbons (PAHs), hopanes, steranes, trace metals, elements, and particle number (PN), were estimated based on roadway measurements. Sampling campaigns were conducted at two different roadways: the CA-110 highway (where only gasoline-powered vehicles are allowed), and the I-710 freeway (where about 20% of the total number of vehicles are diesel-powered trucks). The particulate matter (PM) emission factors determined in these roadways were compared to those reconstructed from recent source emission data from the Caldecott tunnel [Phuleria, H.C., Geller, M.D., Fine, P.M., Sioutas, C., 2006. Size-resolved emissions of organic tracers from light- and heavy-duty vehicles measured in a California roadway tunnel. Environmental Science and Technology 40 (13), 4109–4118], and those from previous tunnel and chassis dynamometer studies. Very good agreement between estimated and reconstructed emission factors was found for PN, EC, sulfate, high-molecular-weight (MW) PAHs, hopanes and steranes. This suggests that PM-speciated chemical data collected at roadsides can be used to calculate reliable emission factors for several important particle species at other locations characterized by a similar mix of on-road motor vehicles. The agreement between our results and other studies in the emission factors of trace elements and metals varied from very good (for species such as Cu, Mo, Ba, Pb) to poor (for species such as Mg, Fe, Ca), probably because the atmospheric concentrations of the latter elements are associated with both traffic and non-traffic sources, and the relative abundances of Mg, Ca, and Fe in road dust varies considerably across locations. The emission factors of OC and EC were clearly the highest for HDVs, and those of PAHs, hopanes, and steranes from our roadway measurements were well within the range of values reported in the literature from tunnel and dynamometer studies. The approach presented in this paper allows for a straight-forward estimation of PM emission factors from ambient, near-freeway measurements. Although the uncertainties inherent in the method proposed here must be acknowledged (e.g. assumptions were made to estimate the average fleet composition and the total carbon content in the vehicles’ exhaust), our results are generally in very good agreement with those in the available literature for most non-labile PM species.

Keywords: Emission factors; Heavy-duty vehicles; Light-duty vehicles; Freeway; Tunnel; OC and EC; Sulfate; PAHs; Hopanes; Steranes; Trace metals and elements; CO; ₂

Influence of sea-salt activated chlorine and surface-mediated renoxification on the weekend effect in the South Coast Air Basin of California by Alexander Cohan; Wayne Chang; Marc Carreras-Sospedra; Donald Dabdub (pp. 3115-3129).

High ozone mixing ratios are a serious concern of public health. While ozone concentrations are high on weekdays due to anthropogenic emissions, they are often higher on weekends. This phenomenon has been named the weekend effect. This study uses the University of California, Irvine-California Institute of Technology (UCI-CIT) air quality model to assess the weekend effect in the South Coast Air Basin (SoCAB) of California. The weekend effect is reproduced by the model using an emissions inventory that includes representative weekday and weekend emissions. Additionally, this study modifies the Caltech Atmospheric Chemistry Mechanism (CACM), used in the UCI-CIT model, by introducing new heterogeneous reactions involving nitrogen oxides and chlorine. Eight modeling scenarios that include the nitrogen oxide renoxification and heterogeneous/multiphase chlorine reactions are presented to quantify how these reactions impact the weekend effect. The renoxification reaction and chlorine chemistry are found to increase ozone levels during weekdays and weekend days. However, increases in weekdays are generally larger than these increases that occur in the weekend. As a result, renoxification and chlorine chemistry lead to a net decrease in the average weekend effect intensity. The influence of renoxification on the weekend effect depends on the reaction probability ( P), and the impact on the weekend effect is significant for P larger than 0.1. The influence of chlorine chemistry on the weekend effect depends strongly on the sea-salt source function that activates the chlorine chemistry. An amplification factor of 10 for the sea-salt source function, which produces the best agreement with observed chlorine levels in the SoCAB, leads to a basin-wide overall decrease of 29% in the weekend effect intensity with respect to the base case.

Keywords: Weekend effect; Atmospheric modeling; Chlorine; Renoxification; Ozone

Assessment of the relative importance of atmospheric aging on CCN activity derived from field observations by Hiroshi Furutani; Manuel Dall’osto; Greg C. Roberts; Kimberly A. Prather (pp. 3130-3142).

The effect of atmospheric aging on the cloud condensation nuclei (CCN) activity of atmospheric aerosols was studied by comparing different air masses with different degrees of aging along the southern coast of California over the Pacific Ocean during a research cruise on the R/V Roger Revelle from 2–19 November 2004. Activation diameters ( D_act) were calculated using the measured CCN concentrations, condensation nuclei (CN) concentrations, and particle size distributions. Measurements of single particle size and chemistry, as well as black carbon (BC) concentrations with an aethalometer, were made to provide further insight into aerosol chemistry. A gradient of aerosol concentrations was encountered: along the coast of California, the highest BC and CN concentrations (1000–6000ngm⁻³ and 2000–15,000cm⁻³) were measured which decreased as the ship moved away from shore to much lower values (<100ngm⁻³, ∼300cm⁻³). In all regions, external mixtures of organic carbon, elemental carbon, sea salt, and dust aerosols frequently associated with nitrate and sulfate were observed. A correlation plot between the CCN/CN ratio and D_act exhibits a clear linear correlation, showing a distinct relationship between the extent of anthropogenic aging and CCN activity with the most highly aged air masses showing the highest CCN activity and smallest D_act. These results show changes in aerosol chemistry due to atmospheric aging that play an important role in determining the CCN activity of atmospheric aerosols. The present study demonstrates that variations in aerosol chemistry must be taken into account in models to adequately account for the physicochemical properties of atmospheric aerosols and their CCN activity.

Keywords: Cloud condensation nuclei; Single particle chemical composition; ATOFMS; Atmospheric aerosol; Atmospheric aging

The Los Angeles International Airport as a source of ultrafine particles and other pollutants to nearby communities by Dane Westerdahl; Scott A. Fruin; Phillip L. Fine; Constantinos Sioutas (pp. 3143-3155).

Air monitoring was performed in the vicinity of the Los Angeles International Airport (LAX) during the spring of 2003. The purpose of this monitoring was to determine the extent of airport emissions on downwind ambient air in a mixed use neighborhood that includes residences. A mobile air monitoring platform was developed and deployed to measure ultrafine particle numbers (UFP), size distributions, particle length, black carbon (BC), oxides of nitrogen (NO _x), and particle-phase polycyclic aromatic hydrocarbons (PM-PAH).Pollutant levels were low at a coastal site upwind of the airport, with UFP ranging between 580 and 3800countscm⁻³, oxides of nitrogen (NO _x) from 4 to 22ppb, black carbon from 0.2 to 0.6μgm⁻³, and PM-PAH ranged from 18 to 36ngm⁻³. Markedly higher UFP counts, with average counts of approximately 50,000cm⁻³, were observed at a site 500m downwind of the airport, which was strongly influenced by aircraft landings and where the community interfaced with airport facilities. Black carbon, PM-PAH, and NO _x levels were elevated to a lesser extent at downwind locations. Transient peaks in UFP corresponding to aircraft landings and takeoffs were evident. A maximum UFP count reached 4.8 million particlescm⁻³ downwind of a runway used by jet aircraft for takeoffs. Particle size distributions differed substantially between upwind and downwind locations. The particle numbers at the upwind site were dominated by particles of approximately 90nm diameter while downwind sites were dominated by particles peaking at approximately 10–15nm. Additional data obtained from a study of UFP levels conducted subsequently by a co-author indicates that aircraft-generated UFP persist up to 900m from an LAX runway [Biswas, S., Fine, P.M., Geller, M.D., Hering, S.V., Sioutas, C., 2005. Performance evaluation of a recently developed water-based condensation particle counter. Aerosol Science and Technology 39, 419–427]. Considered together, these observations suggest that airport operations are associated with elevated levels of UFP much further downwind in the neighboring community than would have been predicted by prior studies of UFP from roadway-traffic.

Keywords: Jet; Particle size; Coastal air; Los Angeles; Black carbon

Variability of East Asia dust events and their long-term trend by Xin Wang; Jianping Huang; Mingxia Ji; Kaz Higuchi (pp. 3156-3165).

In order to examine the decadal variations of the dust events over East Asia, we analyze surface observations from 701 meteorological stations for the period 1960–2004 to obtain spatial and temporal distributions of dust events. Since the Taklamakan Desert in western China and the Gobi Desert in Inner Mongolia are the two major sources of dust storms, we have defined two dust indices, one for the Taklamakan Desert Index (TDI) and one for the Gobi Desert Index (GDI), to characterize the statistical nature of the dust events over these two regions. Both of these indices are well correlated with the Total Ozone Mapping Spectrometer (TOMS) Absorbing Aerosol Index (AAI). TDI and GDI time series exhibit a decreasing trend since the mid-1980s, and is likely caused by an enhanced geopotential height over the Mongolian plateau and the middle Siberian region, as well as by an anomalous shift in the phase and intensity of the stationary wave over.

Keywords: East Asia; Taklamakan Dust Index (TDI); Gobi Dust index (GDI)

Modeling urban and regional aerosols—Development of the UCD Aerosol Module and implementation in CMAQ model by K. Max Zhang; Anthony S. Wexler (pp. 3166-3178).

This paper presents a mechanistic, fully dynamic, internally mixed, sectional aerosol module, the UCD Aerosol Module, which evolves from the Aerosol Inorganic Model (AIM). The UCD Aerosol Module employs three gas-to-particle mass transport schemes, replacement, coupled and uncoupled, and simplified aerosol thermodynamics to predict gas–particle partitioning, aerosol phase state and water content efficiently and reasonably. Aerosol dynamics is integrated using an Asynchronous Time-Stepping (ATS) integration method, where different sized particles integrate with different time scales. CMAQ-UCD is an implementation of the UCD Aerosol Module in the CMAQ modeling system. With all of these features, CMAQ-UCD is designed to be a computationally efficient and scientifically sound air quality model that predicts particulate mass concentrations and size distributions over urban or regional scales for regulatory and scientific purposes.

Keywords: Air quality; Thermodynamics; Particulate matter; Aerosols; Size distribution; PM2.5

Modeling urban and regional aerosols—Application of the CMAQ-UCD Aerosol Model to Tampa, a coastal urban site by C.G. Christopher G. Nolte; P.V. Prakash V. Bhave; J.R. Jeff R. Arnold; R.L. Robin L. Dennis; K.M. K. Max Zhang; A.S. Anthony S. Wexler (pp. 3179-3191).

The University of California at Davis (UCD) aerosol module, an internally mixed, sectional aerosol model with dynamic mass transfer between the gas and particle phases, has been coupled to the Community Multiscale Air Quality (CMAQ) model. This paper describes the application of the CMAQ-UCD model to simulate air quality in Tampa, a large city with a population of 2M on the west coast of Florida, USA. Modeled aerosol size and composition distributions are evaluated against size-segregated ambient measurements ofSO42-,NH4+,NO3-,Na+, andCl- collected at three Tampa-area sites during May 2002, and against semi-continuous HNO₃ and total aerosolSO42-,NH4+,NO3-, andCl- measurements collected at a single site. Sea-salt emissions over the open ocean and the surf zone are parameterized as a function of modeled wind speed and relative humidity. Modeled total aerosol sulfate and ammonium concentrations and size distributions agree with measurements, with an overall normalized mean bias (NMB) of 2% and −23% and normalized mean error (NME) of 46% and 38%, respectively, and correctly identifying the size bin in which the peak concentration is observed. Sea-salt size distributions are also simulated well, with the distribution dominated by the coarse mode and total aerosol sodium and chloride NMB of −2% and 17% and NME of 32% and 38%. Though the model correctly identifies that nitrate is predominantly in the coarse(Dp>2.5μm) size sections, aerosol nitrate concentrations are underpredicted by a factor of two. The availability of highly time-resolved measurements provides a unique opportunity to evaluate the model's partitioning of total nitrate and the simulation of chloride depletion as a function of particle size.

Keywords: Aerosol modeling; Size distribution; Sea salt; BRACE; Chloride depletion

New Directions: Reactive Particles as a Source of Human Health Effects by Philip K. Hopke (pp. 3192-3194).

Sections

Personal tools

Atmospheric Environment (v.42, #13)

Sections

Personal tools

Local resources

Atmospheric Environment (v.42, #13)