Atmospheric Environment (v.43, #16)

Comparative evaluation of nitrogen oxides and ozone passive diffusion tubes for exposure studies by Sotiris Vardoulakis; Julio Lumbreras; Efisio Solazzo (2509-2517).
Passive diffusion tubes are recognised as a cost-effective sampling method for characterising the spatial variability, as well as the seasonal and annual trends, of NO2 concentrations in urban areas. In addition, NOX and O3 passive diffusion tubes have been developed and deployed in urban and rural areas. Despite their many advantages (e.g. low operational and analysis cost, small size and no need for power supply), they have certain limitations mainly related to their accuracy and precision. In particular, the absorbent solution used, the length of the exposure period, the exact location and use of protective devices, and other environmental conditions (e.g. wind, ambient temperature and relative humidity) may have a significant impact on the performance of passive diffusion tubes. The aim of this study is to evaluate the performance of co-located NO2, NOX and O3 diffusion tubes in an urban environment.A one-year passive sampling campaign was carried out in Birmingham (UK) for this purpose. NO2, NOX and O3 diffusion tubes (including triplicate sets of each) were co-located at one urban background and two roadside permanent air quality monitoring stations equipped with standard gas analysers. In addition, meteorological data, such as wind speed and direction, ambient temperature and relative humidity, were obtained during the same period of time. A thorough QA/QC procedure, including storage and laboratory blanks was followed throughout the campaign. The analysis of results showed a very good agreement of NO2 passive samplers with co-located chemiluminescence analysers, but substantial underestimations of total NOX levels by the diffusion tubes. The O3 diffusion sampler appeared to marginally overestimate the automatic UV analyser results, especially during warm weather periods.
Keywords: Passive sampler; Diffusion tubes; Exposure; Urban air pollution; Nitrogen dioxide; Ozone;

We present a numerical study of scalar transport released from a line source downstream of a square obstacle to investigate the capabilities and limitations of gradient-transport modeling in predicting atmospheric dispersion. The standard kɛ and kω models and a Reynolds Stress Transport closure are employed and compared to predict the time-averaged turbulent flow field, while a standard gradient–diffusion model is initially adopted to relate the scalar flux to mean gradients of the concentration field. The analysis of two algebraic closures for turbulent scalar fluxes based on the generalized-gradient–diffusion hypothesis and its quadratic extension is also presented. In spite of the rather simple flow setup, where both the flow and the scalar fields can be assumed homogeneous in the spanwise direction, the analysis clarifies several critical issues concerning gradient-transport type models. We established the dominant role of predicted turbulent kinetic energy on scalar dispersion when a scalar diffusivity is employed, irrespectively of the Reynolds stress closure adopted for the averaged momentum equation. Moreover, the standard gradient–diffusion hypothesis failed to predict the streamwise component of the scalar flux, which is characterized by a counter-gradient-transport mechanism. Although the resulting contribution in the averaged scalar transport equation is small in the present flow configuration, this limitation can become severe for strongly inhomogeneous flows in the presence of point sources, where the spread of the scalar plume is essentially three-dimensional. The predictive capabilities of gradient-transport type modeling are found clearly improved using algebraic closures, which appear to represent a promising tool for predicting atmospheric dispersion in complex flows when unsteady transport mechanisms are not dominant.
Keywords: Scalar dispersion; Obstacle flow; RANS; Finite-volume; Eddy-diffusivity; Algebraic flux models;

To better understand the influence of sources and atmospheric processing on aerosol chemical composition, we collected atmospheric particles in Sapporo, northern Japan during spring and early summer 2005 under the air mass transport conditions from Siberia, China and surrounding seas. The aerosols were analyzed for inorganic ions, organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and the major water-soluble organic compound classes (i.e., dicarboxylic acids and sugars). SO4 2− is the most abundant inorganic constituent (average 44% of the identified inorganic ion mass) followed by NH4 + (21%) and NO3 (13%). Concentrations of OC, EC, and WSOC ranged from 2.0–16, 0.24–2.9, and 0.80–7.9 μg m−3 with a mean of 7.4, 1.0, and 3.1 μg m−3, respectively. High OC/EC ratios (range: 3.6–19, mean: 8.7) were obtained, however WSOC/OC ratios (0.23–0.69, 0.44) do not show any significant diurnal changes. These results suggest that the Sapporo aerosols were already aged, but were not seriously affected by local photochemical processes. Identified water-soluble organic compounds (diacids + sugars) account for <10% of WSOC. Based on some marker species and air mass back trajectory analyses, and using stable carbon isotopic compositions of shorter-chain diacids (i.e., C2–C4) as photochemical aging factor of organic aerosols, the present study suggests that a fraction of WSOC in OC is most likely influenced by aerosol aging, although the OC loading in aerosols may be more influenced by their sources and source regions.
Keywords: Atmospheric aerosols; Major ions; Diacids; Sugars; Water-soluble organic carbon; Organic carbon; Photochemical aging;

A wide area of air pollutant impact downwind of a freeway during pre-sunrise hours by Shishan Hu; Scott Fruin; Kathleen Kozawa; Steve Mara; Suzanne E. Paulson; Arthur M. Winer (2541-2549).
We have observed a wide area of air pollutant impact downwind of a freeway during pre-sunrise hours in both winter and summer seasons. In contrast, previous studies have shown much sharper air pollutant gradients downwind of freeways, with levels above background concentrations extending only 300 m downwind of roadways during the day and up to 500 m at night. In this study, real-time air pollutant concentrations were measured along a 3600 m transect normal to an elevated freeway 1–2 h before sunrise using an electric vehicle mobile platform equipped with fast-response instruments. In winter pre-sunrise hours, the peak ultrafine particle (UFP) concentration (∼95 000 cm−3) occurred immediately downwind of the freeway. However, downwind UFP concentrations as high as ∼40 000 cm−3 extended at least 1200 m from the freeway, and did not reach background levels (∼15 000 cm−3) until a distance of about 2600 m. UFP concentrations were also elevated over background levels up to 600 m upwind of the freeway. Other pollutants, such as NO and particle-bound polycyclic aromatic hydrocarbons, exhibited similar long-distance downwind concentration gradients. In contrast, air pollutant concentrations measured on the same route after sunrise, in the morning and afternoon, exhibited the typical daytime downwind decrease to background levels within ∼300 m as found in earlier studies. Although pre-sunrise traffic volumes on the freeway were much lower than daytime congestion peaks, downwind UFP concentrations were significantly higher during pre-sunrise hours than during the daytime. UFP and NO concentrations were also strongly correlated with traffic counts on the freeway. We associate these elevated pre-sunrise concentrations over a wide area with a nocturnal surface temperature inversion, low wind speeds, and high relative humidity. Observation of such wide air pollutant impact area downwind of a major roadway prior to sunrise has important exposure assessment implications since it demonstrates extensive roadway impacts on residential areas during pre-sunrise hours, when most people are at home.
Keywords: Vehicle-related air pollutants; Ultrafine particles; Mobile platform; Roadway; Exposure assessment;

Reactivity between PbSO4 and CaCO3 particles relevant to the modification of mineral particles and chemical forms of Pb in particles sampled at two remote sites during an Asian dust event by Takahiro Ishizaka; Susumu Tohno; Chang-Jin Ma; Atsushi Morikawa; Masaki Takaoka; Fumitaka Nishiyama; Kouhei Yamamoto (2550-2560).
During the transboundary transport of anthropogenic heavy metals by mineral particles providing reaction sites, the divalent metal salt PbSO4 can be converted to PbCO3 in the presence of water. We carried out laboratory experiments to study the transformation process under various conditions by incorporating test particles comprising CaCO3 of a particulate mineral component, PbSO4, and NaCl. After the immersion of PbSO4 particles in contact with CaCO3 particles in a water droplet, the conversion of PbSO4 into PbCO3 was confirmed by the change in morphology of the original particles to stick or needle form; the percentages of the chemical forms relative to the total Pb were determined by X-ray absorption near edge structure (XANES) analysis. Approximately 60–80% of PbSO4 was converted to PbCO3 after 24 h. A small amount of stick particles was detected when NaCl particles attached to PbSO4/CaCO3 particles were exposed to air with a relative humidity (RH) of 80–90% for 24 h. XANES measurements of the samples revealed that the molar percentage of PbCO3 relative to the total Pb content was 4%.Field experiments were also conducted to determine the chemical forms of the Pb particles during the Kosa (Asian dust storm) event. Samples were collected from two remote sites in Japan and Korea. The mass size distribution of Pb aerosols collected in Japan was bimodal with two peaks in the coarse mode; the enrichment factor of Pb suggested that its source was anthropogenic. Pb L3 edge XANES measurements of both samples indicated that they had similar shapes. These measurements also indicated that the major Pb components for the samples collected in Japan were PbO, PbSO4 PbCl2, and PbCO3, with molar percentages of 44%, 30%, 21%, and 5%, respectively. No significant differences were found between the component ratios of the samples collected in Japan and Korea, suggesting that definite transformation did not occur during the transport of the Kosa particles from Korea to Japan. On the basis of these observations, we postulate that the transformation process either occurred mainly before the particles arrived at Korea or did not take place after the particles left continental Asia.
Keywords: Mineral dust; XANES; Transformation; Deliquescent particles; PbSO4; PbCO3;

A combined model–observation approach to estimate historic gridded fields of PM2.5 mass and species concentrations by Christian Hogrefe; Barry Lynn; Richard Goldberg; Cynthia Rosenzweig; Eric Zalewsky; Winston Hao; Prakash Doraiswamy; Kevin Civerolo; Jia-Yeong Ku; Gopal Sistla; P.L. Kinney (2561-2570).
This paper introduces a methodology for estimating gridded fields of total and speciated fine particulate matter (PM2.5) concentrations for time periods and regions not covered by observational data. The methodology is based on performing long-term regional scale meteorological and air quality simulations and then integrating these simulations with available observational data. To illustrate this methodology, we present an application in which year-round simulations with a meteorological model (the National Center for Atmospheric Research/Penn State Mesoscale Model, hereafter referred to as MM5) and a photochemical air quality model (the Community Multiscale Air Quality Model, hereafter referred to as CMAQ) have been performed over the northeastern United States for 1988–2005. Model evaluation results for total PM2.5 mass and individual species for the time period from 2000 to 2005 show that model performance varies by species, season, and location. Therefore, an approach is developed to adjust CMAQ output with factors based on these three variables. The adjusted model values for total PM2.5 mass for 2000–2005 are compared against independent measurements not utilized for the adjustment approach. This comparison reveals that the adjusted model values have a lower root mean square error (RMSE) and higher correlation coefficients than the original model values. Furthermore, the PM2.5 estimates from these adjusted model values are compared against an alternate method for estimating historic PM2.5 values that is based on PM2.5/PM10 ratios calculated at co-located monitors. Results reveal that both methods yield estimates of historic PM2.5 mass that are broadly consistent; however, the adjusted CMAQ values provide greater spatial coverage and information for PM2.5 species in addition to total PM2.5 mass. Finally, strengths and limitations of the proposed approach are discussed in the context of potential uses of this method.
Keywords: Long-term air quality modeling; Aerosol model evaluation; Air quality characterization; Data integration; Community Multiscale; Air Quality (CMAQ) model;

Nitric oxides and nitrous oxide fluxes from typical vegetables cropland in China: Effects of canopy, soil properties and field management by Xiaobing Pang; Yujing Mu; Xinqing Lee; Shuangxi Fang; Juan Yuan; Daikuan Huang (2571-2578).
In China, vegetable croplands are characterized by intensive fertilization and cultivation, which produce significant nitrogenous gases to the atmosphere. In this study, nitric oxides (NOX) and nitrous oxide (N2O) emissions from the croplands cultivated with three typical vegetables had been measured in Yangtze River Delta of China from September 2 to December 16, 2006. The NO fluxes varied in the ranges of 1.6–182.4, 1.4–2901 and 0.5–487 ng Nm−2 s−1 with averages of 33.8 ± 44.2, 360 ± 590 and 76 ± 112 (mean ± SD) ngNm−2 s−1 for cabbage, garlic, and radish fields (n = 88), respectively. N2O fluxes from the three vegetable fields were found to occur in pulses and significantly promoted by tillage with average values of 5.8, 8.8, and 4.3 ng Nm−2 h−1 for cabbage, garlic, and radish crops, respectively. Influence of vegetables canopy on the NO emission was investigated and quantified. It was found that on cloudy days the canopy can only shield NO emission from croplands soil while on sunny days it cannot only prevent NO emission but also assimilate NO through the open leaves stomas. Multiple linear regression analysis indicated that soil temperature was the most important factor in controlling NO emission, followed by fertilizer amount and gravimetric soil water content. About 1.2%, 11.56% and 2.56% of applied fertilizers N were emitted as NO–N and N2O–N from the cabbage, garlic and radish plots, respectively.
Keywords: Nitrous oxide; Nitric oxide; Vegetables cropland; Yangtze River Delta of China;

In this study, a time-varying statistical model, TVAREX, was proposed for daily averaged PM10 concentrations forecasting of coastal cities. It is a Kalman filter based autoregressive model with exogenous inputs depending on selected meteorological properties on the day of prediction. The TVAREX model was evaluated and compared to an ANN model, trained with the Levenberg–Marquardt backpropagation algorithm subjected to the same set of inputs. It was found that the error statistics of the TVAREX model in general were comparable to those of the ANN model, but the TVAREX model was more efficient in capturing the PM10 pollution episodes due to its online nature, therefore having an appealing advantage for implementation.
Keywords: Air quality prediction; Artificial Neural Network; Kalman filter; Coastal city; Macau; PM10;

The relation of interannual connection between Asian dust outbreaks and stratosphere-to-troposphere transport (STT) in spring was suggested by the dust and tritium variations in the Mount Wrangell ice core, Alaska in [Yasunari, T.J., Shiraiwa, T., Kanamori, S., Fujii, Y., Igarashi, M., Yamazaki, K., Benson, C.S., Hondoh, T., 2007. Intra-annual variations in atmospheric dust and tritium in the North Pacific region detected from an ice core from Mount Wrangell, Alaska. J. Geophys. Res., 112, D10208. doi: 10.1029/2006JD008121]. However, these impacts on the ice core site in each event scale have not been investigated. Hence, the present paper focuses on the material transport and deposition processes for further understanding these impacts on the ice core. The variations in dust and tritium concentrations in spring in an ice core taken at Mt. Wrangell, Alaska are explained by meteorological analysis and simulation of trajectories associated with Asian dust outbreaks and STT. Material transport and deposition at Mt. Wrangell are examined in two contrasting years (2001 and 2002). Dust and tritium concentrations both reached peak values in the early spring of 2002, while the dust peak occurred in early spring and the tritium peak occurred in late spring in 2001. Six severe East Asian transpacific dust storms over this period are modeled by forward trajectory and meteorologically analyzed. It is found that 5 of 6 events contributed to the ice core record in Alaska. Stratospheric air is also transported to the ice core site in most cases. Tritium deposition is found to have been suppressed in the cases of the 2001 dust storms due to lack of snowfall at appropriate times. Taken the detailed transport and deposition processes after the severe dust storms with atmospheric circulations into account, we can well explain spring dust and tritium variations in the Mount Wrangell ice core.
Keywords: Asian dust; Stratosphere-to-troposphere transport (STT); Tritium; Ice core; Climate;

Can we trust odor databases? Example of t- and n-butyl acetate by William S. Cain; Roland Schmidt (2591-2601).
The US EPA has exempted t-butyl acetate from VOC regulations, which increases the likelihood that it may replace other solvents in some settings. This investigation probes its chemosensory properties. In Study 1, subjects (n = 29) sought to detect the odor of t-butyl acetate and of n-butyl acetate in forced-choice testing of stable concentrations, analytically confirmed. Subjects sniffed from cones with a high enough volumetric flow to insure against dilution by nonodorized air. A subject made hundreds of judgments, enough for a psychometric function for each material. The points of 50% detection above chance (“threshold”) occurred at 8 and 2 ppb for t-butyl acetate and n-butyl acetate, respectively. In study 2, subjects (n = 26) sought to detect vapor with the eye via chemesthesis (sensory irritation) in 10-s exposures. Detection at 50% occurred at 177 and 113 ppm for t-butyl acetate and n-butyl acetate, respectively, more than 10,000 times above that for odor detection. The protocols produced results of uncommon precision compared to those in often-misleading archival databases. The nose exhibits much higher sensitivity than the databases indicate. The collections rarely exhibit accuracy better than ±1000%. Collection of accurate data for a VOC can ironically bring on stricter regulation for just it, a situation that calls for a strategy to improve the database by collection of new data, importation of better data, and development of quantitative structure–activity modeling.
Keywords: t-Butyl acetate; n-Butyl acetate; Psychophysics; Odor threshold; Ocular irritation;

Testing Lagrangian atmospheric dispersion modelling to monitor CO2 and CH4 leakage from geosequestration by Zoë Loh; Ray Leuning; Steve Zegelin; David Etheridge; Mei Bai; Travis Naylor; David Griffith (2602-2611).
We assess the performance of an inverse Lagrangian dispersion technique for its suitability to quantify leakages from geological storage of CO2. We find the technique is accurate ( 〈 Q bLS / Q 〉 = 0.99 , σ = 0.29 ) when strict meteorological filtering is applied to ensure that Monin–Obukhov Similarity Theory is valid for the periods analysed and when downwind enrichments in tracer gas concentration are 1% or more above background concentration. Because of their respective baseline atmospheric concentrations, this enrichment criterion is less onerous for CH4 than for CO2. Therefore for geologically sequestered gas reservoirs with a significant CH4 component, monitoring CH4 as a surrogate for CO2 leakage could be as much as 10 times more sensitive than monitoring CO2 alone. Additional recommendations for designing a robust atmospheric monitoring strategy for geosequestration include: continuous concentration data; exact inter-calibration of up- and downwind concentration measurements; use of an array of point concentration sensors to maximise the use of spatial information about the leakage plume; and precise isotope ratio measurement to confirm the source of any concentration elevations detected.
Keywords: Backward Lagrangian dispersion; Greenhouse gas storage; Atmospheric monitoring of geosequestration; Carbon capture and storage; CCS;

Rapid measurement of emissions from military aircraft turbine engines by downstream extractive sampling of aircraft on the ground: Results for C-130 and F-15 aircraft by Chester W. Spicer; Michael W. Holdren; Kenneth A. Cowen; Darrell W. Joseph; Jan Satola; Bradley Goodwin; Howard Mayfield; Alexander Laskin; M. Lizabeth Alexander; John V. Ortega; Matthew Newburn; Robert Kagann; Ram Hashmonay (2612-2622).
Aircraft emissions affect air quality on scales from local to global. More than 20% of the jet fuel used in the U.S. is consumed by military aircraft, and emissions from this source are facing increasingly stringent environmental regulations, so improved methods for quickly and accurately determining emissions from existing and new engines are needed. This paper reports results of a study to advance the methods used for detailed characterization of military aircraft emissions, and provides emission factors for two aircraft: the F-15 fighter and the C-130 cargo plane. The measurements involved outdoor ground-level sampling downstream behind operational military aircraft. This permits rapid change-out of the aircraft so that engines can be tested quickly on operational aircraft. Measurements were made at throttle settings from idle to afterburner using a simple extractive probe in the dilute exhaust. Emission factors determined using this approach agree very well with those from the traditional method of extractive sampling at the exhaust exit. Emission factors are reported for CO2, CO, NO, NO x , and more than 60 hazardous and/or reactive organic gases. Particle size, mass and composition also were measured and are being reported separately. Comparison of the emissions of nine hazardous air pollutants from these two engines with emissions from nine other aircraft engines is discussed.
Keywords: Jet engine emissions; Turbine engine; Emission factor; Emission index; Hazardous air pollutants; Afterburner emissions; Military aircraft;

Municipal solid waste landfills are the significant anthropogenic sources of N2O due to the cooxidation of ammonia by methane-oxidizing bacteria in cover soils. Such bacteria could be developed through CH4 fumigation, as evidenced by both laboratory incubation and field measurement. During a 10-day incubation with leachate addition, the average N2O fluxes in the soil samples, collected from the three selected landfill covers, were multiplied by 1.75 (p < 0.01), 3.56 (p < 0.01), and 2.12 (p < 0.01) from the soil samples preincubated with 5% CH4 for three months when compared with the control, respectively. Among the three selected landfill sites, N2O fluxes in two landfill sites were significantly correlated with the variations of the CH4 emissions without landfill gas recovery (p < 0.001). N2O fluxes were also elevated by the increase of the CH4 emissions with landfill gas recovery in another landfill site (p > 0.05). The annual average N2O flux was 176 ± 566 μg N2O–N m−2 h−1 (p < 0.01) from sandy soil–covered landfill site, which was 72% (p < 0.05) and 173% (p < 0.01) lower than the other two clay soil covered landfill sites, respectively. The magnitude order of N2O emissions in three landfill sites was also coincident by the results of laboratory incubation, suggesting the sandy soil cover could mitigate landfill N2O emissions.
Keywords: Municipal solid waste landfill; N2O emissions; CH4 emissions; Methanotrophic nitrification; Cover soil type;

Characterisation of particulate matter and gaseous emissions from a large ship diesel engine by Jana Moldanová; Erik Fridell; Olga Popovicheva; Benjamin Demirdjian; Victoria Tishkova; Alessandro Faccinetto; Cristian Focsa (2632-2641).
Composition of exhaust from a ship diesel engine using heavy fuel oil (HFO) was investigated onboard a large cargo vessel. The emitted particulate matter (PM) properties related to environmental and health impacts were investigated along with composition of the gas-phase emissions. Mass, size distribution, chemical composition and microphysical structure of the PM were investigated. The emission factor for PM was 5.3 g (kg fuel)−1. The mass size distribution showed a bimodal shape with two maxima: one in the accumulation mode with mean particle diameter D P around 0.5 μm and one in the coarse mode at D P around 7 μm. The PM composition was dominated by organic carbon (OC), ash and sulphate while the elemental carbon (EC) composed only a few percent of the total PM. Increase of the PM in exhaust upon cooling was associated with increase of OC and sulphate. Laser analysis of the adsorbed phase in the cooled exhaust showed presence of a rich mixture of polycyclic aromatic hydrocarbon (PAH) species with molecular mass 178–300 amu while PM collected in the hot exhaust showed only four PAH masses.Microstructure and elemental analysis of ship combustion residuals indicate three distinct morphological structures with different chemical composition: soot aggregates, significantly metal polluted; char particles, clean or containing minerals; mineral and/or ash particles. Additionally, organic carbon particles of unburned fuel or/and lubricating oil origin were observed. Hazardous constituents from the combustion of heavy fuel oil such as transitional and alkali earth metals (V, Ni, Ca, Fe) were observed in the PM samples.Measurements of gaseous composition in the exhaust of this particular ship showed emission factors that are on the low side of the interval of global emission factors published in literature for NO x , hydrocarbons (HC) and CO.
Keywords: Ship emissions; Particulate matter; Chemical composition; Elemental composition; Microphysical characteristic; NO x ; CO; SO2; Hydrocarbons;

This study investigated the emissions of carbonyl compounds (CBCs) and regulated harmful matters (traditional pollutants) from an HDDE (heavy-duty diesel engine) at one low load steady-state condition, 24.5% of the max load (40 km h−1), using five test fuels: premium diesel fuel (D100), P100 (100% palm-biodiesel), P20 (20% palm-biodiesel + 80% premium diesel fuel), PF80P20 (80% paraffinic fuel + 20% palm-biodiesel), and PF95P05 (95% paraffinic fuel + 5% palm-biodiesel). Experimental results indicate that formaldehyde was the major carbonyl in the exhaust, accounting for 70.3–75.4% of total CBC concentrations for all test fuels. Using P100 and P20 instead of D100 in the HDDE increased CBC concentrations by 9.74% and 2.89%, respectively. However, using PF80P20 and PF95P05 as alternative fuels significantly reduced CBC concentrations by 30.3% and 24.2%, respectively. Using PF95P05 instead of D100 decreased CBCs by 30.3%, PM by 11.1%, THC by 39.0%, CO by 34.0%, NOx by 24.3%, and CO2 by 7.60%. The wide usage of paraffinic–palmbiodiesel blends as alternative fuels could protect the environment. However, it should be noted that only one engine operated at one low load steady-state condition was investigated.
Keywords: Carbonyl compounds; Emission; Biodiesel; Paraffinic fuel; Diesel engine; Regulated harmful matters;

Characterisation of soil emissions of nitric oxide at field and laboratory scale using high resolution method by P. Laville; D. Flura; B. Gabrielle; B. Loubet; O. Fanucci; M.-N. Rolland; P. Cellier (2648-2658).
Agricultural soils may account for 10% of anthropogenic emissions of NO, a precursor of tropospheric ozone with potential impacts on air quality and global warming. However, the estimation of this biogenic source strength and its relationships to crop management is still challenging because of the spatial and temporal variability of the NO fluxes.Here, we present a combination of new laboratory- and field-scale methods to characterise NO emissions and single out the effects of environmental drivers.First, NO fluxes were continuously monitored over the growing season of a maize-cropped field located near Paris (France), using 6 automatic chambers. Mineral fertilizer nitrogen was applied from May to October 2005. An additional field experiment was carried out in October to test the effects of N fertilizer form on the NO emissions. The automatic chambers were designed to measure simultaneously the NO and N2O gases. Laboratory measurements were carried out in parallel using soil cores sampled at same site to test the response of NO fluxes to varying soil N–NH4 and water contents, and temperatures. The effects of soil core thickness were also analysed.The highest NO fluxes occurred during the first 5 weeks following fertilizer application. The cumulative loss of NO–N over the growing season was estimated at 1.5 kg N ha−1, i.e. 1.1% of the N fertilizer dose (140 kg N ha−1). All rainfall events induced NO peak fluxes, whose magnitude decreased over time in relation to the decline of soil inorganic N. In October, NO emissions were enhanced with ammonium forms of fertilizer N. Conversely, the application of nitrate-based fertilizers did not significantly increase NO emissions compared to an unfertilized control. The results of the subsequent laboratory experiments were in accordance with the field observations in magnitude and time variations. NO emissions were maximum with a water soil content of 15% (w w−1), and with a NH4–N content of 180 mg NH4–N kg soil−1. The response of NO fluxes to soil temperature was fitted with two exponential functions, involving a Q 10 of 2.0 below 20 °C and a Q 10 of 1.4 above. Field and laboratory experiments indicated that most of the NO fluxes originated from the top 10 cm of soil. The characterisation of this layer in terms of mean temperature, NH4 and water contents is thus paramount to explaining the variations of NO fluxes.
Keywords: Nitric oxide emission; NO; Agriculture; Nitrification; Denitrification; Environmental factors;

Characterization of African Dust (PM2.5) across the Atlantic Ocean during AEROSE 2004 by Braulio Jiménez-Vélez; Yasmín Detrés; Roy A. Armstrong; Adriana Gioda (2659-2664).
An Aerosol and Oceanographic Science Expedition (AEROSE) on the NOAA Ship Ronald H. Brown collected PM2.5 particles from a Saharan dust storm in March 2004. High levels of PM2.5 (120 μg m−3) were measured during this Saharan storm over the Atlantic Ocean. The particles were characterized for trace element content, with Al and Fe the most abundant metals. These metals were detected in high concentrations during the Saharan event and exhibited good correlations with PM2.5, suggesting its soil origin. Other elements (Pb, Ni, Cd) did not correlate with Al and Fe, indicating their anthropogenic origin. Enrichment factor calculation conducted on these trace elements support our findings. Trace element analyses performed on particulate matter from a reference site on land in Puerto Rico (Fajardo), demonstrated similar results to those obtained in the AEROSE expedition, where high concentrations of PM2.5 and Fe were present concomitantly with Saharan events at this station.
Keywords: Saharan dust; Heavy metals; PM2.5; Arsenic; Enrichment factor;

NOX fluxes from three kinds of vegetable lands and a rice field were measured during summer–autumn in the Yangtze Delta, China. The average NO fluxes from the rice fields (RF), celery field (CE), maize field (MA) and cowpea field (CP) were 4.1, 30.8, 54 and 32.2 ng N m−2 s−1, respectively; and the average NO2 fluxes were −2.12, 0.68, 1.33 and 0.5 ng N m−2 s−1, respectively. The liquid N fertilizer (the mixture of swine excrement and urine) which is widely applied to vegetable lands by Chinese farmers was found to quickly stimulate NO emission, and have significant contribution to NO emission from the investigated vegetable lands. Apparent linearity correlations were found between NO2 fluxes and the ambient concentrations of the rice fields, with a compensation point of about 2.84 μg m−3. Total emissions of NO during summer–autumn time from this area were roughly estimated to be 4.1 and 8.4 Gg N for rice field and vegetable lands, respectively.
Keywords: NOX; Flux; Agricultural lands; Rice; Vegetable;

A tethered balloon sampling system was used to measure vertical profiles of ozone, particles, and solar radiation in the atmospheric boundary layer on the northern edge of Mexico City, in March 2006 as part of the Megacity Impact on Regional and Global Environment-Mexico experiment. Several commercial sensors, designed for surface applications, were deployed on a tethered balloon platform.Profiles indicate that for these 3 scalars the boundary layer (surface up to 700 m) was well mixed in the period 10:00–16:00 LST. Good agreement was observed for median surface and balloon ozone and particle number concentrations. For most profiles, the surface deposition of ozone was not significant compared to median profile concentrations. Particle number concentration (0.3, 0.5, 1.0 and 5.0 μm) also showed little variation with attitude. Radiatprofiles showed a monotonic increase in diffuse radiation from the maximum altitude of profiles to the surface. Consequently, it was inferred that surface measurements of these likely were representative of lower boundary layer values during this time period.
Keywords: Tethered balloon; Boundary layer; Megacity; Ozone; Radiation; Particles;

Assessment of rainwater volatile organic carbon in southeastern North Carolina, USA by G.B. Avery; J.L. Dickson Brown; J.D. Willey; R.J. Kieber (2678-2681).
Extensive production of ethanol and vehicular use of this biofuel have recently been suggested as possible sources of elevated volatile organic carbon (VOC) in rain in Brazil (Campos, M.L.A.M., Nogueira, R.F.P., Dametto, P.R., Francisco, J.G., Coelho, C.H., 2007. Dissolved organic carbon in rainwater: glassware decontamination and sample preservation and volatile organic carbon. Atmos. Environ. 41, 8924–8931; Coelho, C.H., Francisco, J.G., Nogueira, R.F.P., Campos, M.L.A.M., 2008. Dissolved organic carbon in rainwater from areas heavily impacted by sugar cane burning. Atmos. Environ. 42, 7115–7121). Furthermore, these studies suggested that the global flux of rainwater dissolved organic carbon (DOC) may be underestimated since most DOC analytical methods do not measure VOC. The current study examined rain VOC in Wilmington, North Carolina USA in order to assess the importance of rain VOC in a location that does not have the unique conditions of ethanol production and usage found in Brazil. VOC was observed in one of six whole rain events analyzed in the current study. This event had an air mass back trajectory that originated over the Midwestern USA, the primary region where ethanol is produced and used as fuel. The other five storms which had no influence from the central US prior to arrival at the rain collection site had non-detectable VOC suggesting that air mass back trajectory has a dramatic impact on the VOC content of rainwater. VOC was also observed in the initial 1 mm of rain from two of these events but was not detectable in the whole event samples suggesting VOC is efficiently washed out of the atmosphere and is not rapidly resupplied in rainwater at this location. Considering the results of the previous Brazilian studies and the current study, and the likelihood of increased global production and consumption of ethanol based biofuels, it is imperative that future measurements of rainwater DOC include measurement of VOC. Monitoring changes in the VOC contribution to rain DOC will provide an assessment of the impact of increased ethanol biofuel usage on rainwater composition and allow for future refinements of global rainwater DOC flux estimates.
Keywords: Volatile organic carbon; Dissolved organic carbon; Rainwater; Precipitation;