Atmospheric Environment (v.44, #23)

Characterization of carbon fractions for atmospheric fine particles and nanoparticles in a highway tunnel by Chong-Shu Zhu; Cheng-Chieh Chen; Jun-Ji Cao; Chuen-Jinn Tsai; Charles C.-K. Chou; Shaw-Chen Liu; Gwo-Dong Roam (2668-2673).
Fine particles (PM2.5) and nanoparticles (PM0.1) were sampled using Dichotomous sampler and MOUDI, respectively, in Xueshan Tunnel, Taiwan. Eight carbon fractions were analyzed using IMPROVE thermal-optical reflectance (TOR) method. The concentrations of different temperature carbon fractions (OC1–OC4, EC1–EC3) in both PM2.5 and PM0.1 were measured and the correlations between OC and EC were discussed. Results showed that the ratios of OC/EC were 1.26 and 0.67 for PM2.5 and PM0.1, respectively. The concentration of EC1 was found to be more abundant than other elemental carbon fractions in PM2.5, while the most abundant EC fraction in PM0.1 was found to be EC2. The variation of contributions for elemental carbon fractions was different among PM2.5 and PM0.1 samples, which was partly owing to the metal catalysts for soot oxidation. The correlations between char-EC and soot-EC showed that char-EC dominated EC in PM2.5 while soot-EC dominated EC in PM0.1. Using eight individual carbon fractions, the gasoline and diesel source profiles of PM0.1 and PM2.5 were extracted and analyzed with the positive matrix factorization (PMF) method.
Keywords: Elemental carbon; Organic carbon; Tunnel; Source profiles;

Comprehensive analysis of the carbon impacts of vehicle intelligent speed control by David C. Carslaw; Paul S. Goodman; Frank C.H. Lai; Oliver M.J. Carsten (2674-2680).
In recent years sophisticated technologies have been developed to control vehicle speed based on the type of road the vehicle is driven on using Global Positioning Systems and in-car technology that can alter the speed of the vehicle. While reducing the speed of road vehicles is primarily of interest from a safety perspective, vehicle speed is also an important determinant of vehicle emissions and thus these technologies can be expected to have impacts on a range of exhaust emissions. This work analyses the results from a very large, comprehensive field trial that used 20 instrumented vehicles with and without speed control driven almost 500,000 km measuring vehicle speed at 10 Hz. We develop individual vehicle modal emissions models for CO2 for 30 Euro III and Euro IV cars at a 1-Hz time resolution. Generalized Additive Models were used to describe how emissions from individual vehicles vary depending on their driving conditions, taking account of variable interactions and time-lag effects. We quantify the impact that vehicle speed control has on-vehicle emissions of CO2 by road type, fuel type and driver behaviour. Savings in CO2 of ≈6% were found on average for motorway-type roads when mandatory speed control was used compared with base case conditions. For most other types of road, speed control has very little effect on emissions of CO2 and in some cases can result in increased emissions for low-speed limit urban roads. We also find that there is on average a 20% difference in CO2 emission between the lowest and highest emitting driver, which highlights the importance of driver behaviour in general as a means of reducing emissions of CO2.
Keywords: Vehicle emissions; Intelligent speed adaptation; Emission inventory; Fuel consumption;

Influence of boundary conditions on CMAQ simulations over the Iberian Peninsula by Rafael Borge; Javier López; Julio Lumbreras; Adolfo Narros; Encarnación Rodríguez (2681-2695).
The influence of chemical boundary conditions (BC) on the response of the Community Multiscale Air Quality (CMAQ) model over the Iberian Peninsula was investigated in this study. Three strategies to supply boundary conditions in the context of the Integrated Assessment Modelling System for the Iberian Peninsula (SIMCA) were tested. Alternative methods consist in providing BC from (1) fixed, time-independent, concentration profiles, (2) concentrations predicted in a CMAQ mother domain (48 km, 1 h resolution) and (3) concentration values from the GEOS-Chem chemical-transport global model (2 × 2.5°, 3 h resolution). High resolution (3 km) simulated concentrations of the main pollutants (NO2, NO, SO2, O3, PM10 and PM2.5) were compared through a comprehensive statistical analysis including observational data from 165 monitoring stations all over the Iberian Peninsula. It was found that model sensitivity to BC for nitrogen and sulphur oxides was limited, being restricted to the vicinity of model boundaries. However, significant domain-wide differences were found when modelling ozone and PM depending on the BC provided to run the tests. Although model performance was affected by spatial and seasonal factors, the results indicate that model-derived, dynamic BC improved CMAQ predictions when compared to those based on static concentrations prescribed in the boundaries. Aggregated statistics suggest that the GEOS-Chem produced the best results for O3 and PM2.5 while NO2 and PM10 were slightly better predicted under the CMAQ nesting approach. Besides the statistical evaluation some other relevant issues in the context of Integrated Assessment Modelling (IAM) are discussed to gain a better insight into the suitability of the methods analyzed and limitations of downscaling methods. Despite being useful to get a better understanding of the role of BC in SIMCA, this study contributed to highlight model deficiencies and therefore to point out future research needs to improve IAM activities in the Iberian Peninsula.
Keywords: Air quality modelling; Boundary conditions; Sensitivity analysis; CMAQ; Iberian Peninsula;

Soil CO2 fluxes from direct seeding rice fields under two tillage practices in central China by Cheng-fang Li; Zhi-kui Kou; Jin-hua Yang; Ming-li Cai; Jin-ping Wang; Cou-gui Cao (2696-2704).
Agricultural practices affect the production and emission of carbon dioxide (CO2) from paddy soils. It is crucial to understand the effects of tillage and N fertilization on soil CO2 flux and its influencing factors for a better comprehension of carbon dynamics in subtropical paddy ecosystems. A 2-yr field study was conducted to assess the effects of tillage (conventional tillage [CT] and no-tillage [NT]) and N fertilization (0 and 210 kg N ha−1) on soil CO2 fluxes during the 2008 and 2009 rice growing seasons in central China. Treatments were established following a split-plot design of a randomized complete block with tillage practices as the main plot and N fertilizer level as the split-plot treatment. The soil CO2 fluxes were measured 24 times in 2008 and 17 times in 2009. N fertilization did not affect soil CO2 emissions while tillage affected soil CO2 emissions, where NT had similar soil CO2 emissions to CT in 2008, but in 2009, NT significantly increased soil CO2 emissions. Cumulative CO2 emissions were 2079–2245 kg CO2–C ha−1 from NT treatments, and 2084–2141 kg CO2–C ha−1 from CT treatments in 2008, and were 1257–1401 kg CO2–C ha−1 from NT treatments, and 1003–1034 kg CO2–C ha−1 from CT treatments in 2009, respectively. Cumulative CO2 emissions were significantly related to aboveground biomass and soil organic C. Before drainage of paddy fields, soil CO2 fluxes were significantly related to soil temperature with correlation coefficients (R) of 0.67–0.87 in 2008 and 0.69–0.85 in 2009; moreover, the Q10 values ranged from 1.28 to 1.55 and from 2.10 to 5.21 in 2009, respectively. Our results suggested that NT rice production system appeared to be ineffective in decreasing carbon emission, which suggested that CO2 emissions from integrated rice-based system should be taken into account to assess effects of tillage.
Keywords: CO2 fluxes; Conventional tillage; Cumulative CO2 emissions; N fertilization; No-tillage;

The seasonal cycles and photochemistry of C2–C5 alkanes at Mace Head by Emma L. Yates; Richard G. Derwent; Peter G. Simmonds; Brian R. Greally; Simon O’Doherty; Dudley E. Shallcross (2705-2713).
Continuous in-situ measurements of NMHCs at Mace Head, Ireland during two full annual cycles from January 2005 to January 2007 were used to investigate NMHC emission sources and transport including dilution and photochemical oxidation. The Mace Head research station is ideally located to sample a wide range of air masses including polluted European transport, clean North Atlantic and Arctic air masses and the ultra-clean, Southern Atlantic air masses. The variety in air mass sampling is used to investigate interaction of emissions, transport, dilution and photochemistry. Variability of long-lived hydrocarbon ratios is used to assess and estimate typical transport times from emission source to the Mace Head receptor. Seasonality in the ratios of isomeric alkane pairs (for butane and pentanes) are used to assess the effects of atmospheric transport and photochemical ageing. Finally, the natural logarithms of NMHC ratios are used to assess photochemical oxidation.
Keywords: NMHCs; Alkanes; Seasonal variation; Photochemical oxidation; Mace Head;

Anthropogenic mercury emission inventory with emission factors and total emission in Korea by Jeong-Hun Kim; Jung-Min Park; Sang-Bo Lee; Deepak Pudasainee; Yong-Chil Seo (2714-2721).
Mercury emissions concentrations, emission factors, and the total national emission from major anthropogenic sources in Korea for the year 2007 were estimated. Uncontrolled and controlled mercury emission factors and the total emission from each source types are presented. The annual national mercury emission from major anthropogenic sources for the year 2007, on average was 12.8 ton which ranged from 6.5 to 20.2 ton. Averaged emissions of elemental, oxidized, and particulate mercury were estimated at 8.25 ton, 3.69 ton, and 0.87 ton, respectively. Due to the removal of a major portion of particulate and oxidized mercury species, elemental mercury was dominant in stack emission. About 54.8% of mercury emission was contributed by industrial sources, 45.0% by stationary combustion sources and 0.02% by mobile sources. Thermal power plants, oil refineries, cement kilns and incinerators (municipal, industrial, medical, sewage sludge) were the major mercury emitters, contributing about 26%, 25%, 21% and 20%, respectively to the total mercury emission. Other sources (crematory, pulp and paper manufacturing, nonferrous metals manufacturing, glass manufacturing) contributed about 8% of the total emission. Priority should be given in controlling mercury emissions from coal-fired power plants, oil refineries, cement kilns and waste incinerators. More measurements including natural and re-emission sources are to be carried out in the future in order to have a clear scenario of mercury emission from the country and to apply effective control measures.
Keywords: Mercury emission; Anthropogenic sources; Emission factors; Mercury speciation;

Carbon dioxide fluxes over an urban park area by Klaus Kordowski; Wilhelm Kuttler (2722-2730).
From September 2006 to October 2007 turbulent fluxes of carbon dioxide were measured at an urban tower station (26 m above ground level, z/zh  = 1.73) in Essen, Germany, using the eddy covariance technique. The site was located at the border between a public park area (70 ha) in the south–west of the station and suburban/urban residential as well as light commercial areas in the north and east of the tower. Depending on the land-use two different sectors (park and urban) were identified showing distinct differences in the temporal evolution of the surface-atmosphere exchange of CO2. While urban fluxes appear to be governed by anthropogenic emissions from domestic heating and traffic (average flux 9.3 μmol m−2 s−1), the exchange of CO2 was steered by biological processes when the park contributed to the flux footprint. The diurnal course during the vegetation period exhibited negative daytime fluxes up to −10 μmol m−2 s−1 on average in summer. Nevertheless, with a mean of 0.8 μmol m−2 s−1 park sector fluxes were slightly positive, thus no net carbon uptake by the surface occurred throughout the year.In order to sum the transport of CO2 a gap-filling procedure was performed by means of artificial neural network generalisation. Using additional meteorological inputs the daily exchange of CO2 was reproduced using radial basis function networks (RBF). The resulting yearly sum of 6031 g m−2 a−1 indicates the entire study site to be a considerable source of CO2.
Keywords: Carbon dioxide; Flux; Essen; Germany; Urban surface; Park; Eddy covariance; Artificial neural networks;

Source apportionment using positive matrix factorization on daily measurements of inorganic and organic speciated PM2.5 by Steven J. Dutton; Sverre Vedal; Ricardo Piedrahita; Jana B. Milford; Shelly L. Miller; Michael P. Hannigan (2731-2741).
Particulate matter less than 2.5 microns in diameter (PM2.5) has been linked with a wide range of adverse health effects. Determination of the sources of PM2.5 most responsible for these health effects could lead to improved understanding of the mechanisms of such effects and more targeted regulation. This has provided the impetus for the Denver Aerosol Sources and Health (DASH) study, a multi-year source apportionment and health effects study relying on detailed inorganic and organic PM2.5 speciation measurements.In this study, PM2.5 source apportionment is performed by coupling positive matrix factorization (PMF) with daily speciated PM2.5 measurements including inorganic ions, elemental carbon (EC) and organic carbon (OC), and organic molecular markers. A qualitative comparison is made between two models, PMF2 and ME2, commonly used for solving the PMF problem. Many previous studies have incorporated chemical mass balance (CMB) for organic molecular marker source apportionment on limited data sets, but the DASH data set is large enough to use multivariate factor analysis techniques such as PMF.Sensitivity of the PMF2 and ME2 models to the selection of speciated PM2.5 components and model input parameters was investigated in depth. A combination of diagnostics was used to select an optimum, 7-factor model using one complete year of daily data with pointwise measurement uncertainties. The factors included 1) a wintertime/methoxyphenol factor, 2) an EC/sterane factor, 3) a nitrate/polycyclic aromatic hydrocarbon (PAH) factor, 4) a summertime/selective aliphatic factor, 5) an n-alkane factor, 6) a middle-oxygenated PAH/alkanoic acid factor and 7) an inorganic ion factor. These seven factors were qualitatively linked with known PM2.5 emission sources with varying degrees of confidence. Mass apportionment using the 7-factor model revealed the contribution of each factor to the mass of OC, EC, nitrate and sulfate. On an annual basis, the majority of OC and EC mass was associated with the summertime/selective aliphatic factor and the EC/sterane factor, respectively, while nitrate and sulfate mass were both dominated by the inorganic ion factor. This apportionment was found to vary substantially by season. Several of the factors identified in this study agree well with similar assessments conducted in St. Louis, MO and Pittsburgh, PA using PMF and organic molecular markers.
Keywords: Particulate matter; PM2.5; Organic molecular markers; Source apportionment; Positive matrix factorization; Denver;

Concentrations of PAHs, and nitro- and methyl- derivatives associated with a size-segregated urban aerosol by Patrizia Di Filippo; Carmela Riccardi; Donatella Pomata; Francesca Buiarelli (2742-2749).
Size-segregated atmospheric particles were collected in Rome, Italy, using a low-pressure impactor.Twelve sampling campaigns were conducted under different meteorological conditions over a whole year covering 155 not consecutive days. The samples were analyzed for polycyclic aromatic hydrocarbons (PAHs) and their nitro- and methyl- derivatives known for their toxicity. An assessment of the carcinogenic potency of the particles known to penetrate into lungs, liver, heart and nervous system was performed.The distribution of the classes of compounds was unimodal and centrated at 0.4 μm size fraction for PAHs and bimodal and centrated at 0.1 and 0.4 μm for methyl- and nitro- derivatives. The 18% of toxic organic compounds we analyzed was distributed into the ultrafine fraction (PM0.1) and 76% in the fine fraction; but substituted PAH distribution in the ultrafine particles shifted toward higher values during warm periods. In July, the 50% of the total nitro-PAHs was found in PM0.1 and an average of 42% of the total methyl-PAHs was found in the same fraction in summer and intermediate seasons.An evaluation of the potential toxicity of the measured compounds was tentatively assessed based on Potency Equivalency Factors (PEF).
Keywords: Size-distribution; Ultrafine particles; Low pressure impactor;

Particulate organic compounds emitted from experimental wildland fires in a Mediterranean ecosystem by C.A. Alves; C. Gonçalves; M. Evtyugina; C.A. Pio; F. Mirante; H. Puxbaum (2750-2759).
Fine (PM2.5) and coarse (PM2.5–10) smoke particles from controlled biomass burnings of a shrub-dominated forest in Lousã Mountain, Portugal, enabled the quantification by chromatographic techniques of several molecular tracers for the combustion of Mediterranean forest ecosystems, which could be conducive to source apportionment studies. The major organic components in the smoke samples were pyrolysates of vegetation cuticles, mainly comprising steradienes and sterol derivatives, carbohydrates from the breakdown of cellulose, aliphatic lipids from vegetation waxes and methoxyphenols from the lignin thermal degradation. Most of these compounds are chiefly found in fine particles. Polycyclic aromatic hydrocarbons (PAH) were also present as minor constituents. Anhydrosugar and PAH molecular diagnostic ratios were applied as source assignment tools. Some biomarkers are reported for the first time in biomass burning smoke.
Keywords: Forest fires; Smoke particles; OC; Organic speciation; Tracers;

Influence of air flow rate on emission of DEHP from vinyl flooring in the emission cell FLEC: Measurements and CFD simulation by Per Axel Clausen; Zhe Liu; Ying Xu; Vivi Kofoed-Sørensen; John C. Little (2760-2766).
The emission of di-(2-ethylhexyl)phthalate (DEHP) from one type of vinyl flooring with ∼15% (w/w) DEHP as plasticizer was measured at 22 °C in five FLECs + one blank FLEC (Field and Laboratory Emission Cell). Initially, the flow through all FLECs was 450 ml min−1. After 689 days the flows were changed to 1000 ml min−1, 1600 ml min−1, 2300 ml min−1, and 3000 ml min−1, respectively, in four FLECs, and kept at 450 ml min−1 in one FLEC. Air samples were collected from the effluent air at regular intervals. After 1190 days the experiments were terminated and the interior surfaces of all six FLECs were rinsed with methanol to estimate the internal surface concentrations of DEHP. The DEHP air concentration and specific emission rate (SER) at steady state was estimated for the five different flow rates. The steady-state concentrations decreased slightly with increasing air flow with only the two highest flow rates resulting in significantly lower concentrations. In contrast, the SERs increased significantly. Despite large variation, the internal surface concentrations appeared to decrease slightly with increasing FLEC flow. Computational fluid dynamic (CFD) simulations suggest that the interior gas and surface concentrations were roughly uniform for the low flow case (450 ml min−1), under which, the partitioning between the FLEC internal surface and chamber air was examined. Although paired t-tests showed no difference between CFD and experimental results for DEHP air concentrations and SERs at steady-state conditions, CFD indicated that the experimental DEHP surface concentrations in the FLECs were underestimated. In conclusion, the experiments showed that the emission of DEHP from vinyl flooring is subject to “external” control and that the SER is strongly and positively dependent on the air exchange rate. However, the increased SER almost compensates for the decrease in gas-phase concentration caused by the increased air exchange.
Keywords: PVC; DEHP; FLEC; Emission; Chamber; CFD;

Responses of future air quality to emission controls over North Carolina, Part II: Analyses of future-year predictions and their policy implications by Yang Zhang; Xiao-Huan Liu; Kristen M. Olsen; Wen-Xing Wang; Bebhinn A. Do; George M. Bridgers (2767-2779).
The MM5/CMAQ system evaluated in Part I paper is applied to study the impact of emission control on future air quality over North Carolina (NC). Simulations are conducted at a 4-km horizontal grid resolution for four one-month periods, i.e., January, June, July, and August 2009 and 2018. Simulated PM2.5 in 2009 and 2018 show distribution patterns similar to those in 2002. PM2.5 concentrations over the whole domain in January and July reduced by 5.8% and 23.3% in 2009 and 12.0% and 35.6% in 2018, respectively, indicating that the planned emission control strategy has noticeable effects on PM2.5 reduction in this region, particularly in summer. More than 10% and 20% of 1-h and 8-h O3 mixing ratios are reduced in July 2009 and 2018, respectively, demonstrating the effectiveness of emission control for O3 reduction in summer. However, O3 mixing ratios in January 2009 and 2018 increase by more than 5% because O3 chemistry is VOC-limited in winter and the effect of NOx reduction dominates over that of VOC reduction under such a condition. The projected emission control simulated at 4-km will reduce the number of sites in non-attainment for max 8-h O3 from 49 to 23 in 2009 and to 1 in 2018 and for 24-h average PM2.5 from 1 to 0 in 2009 and 2018 based on the latest 2008 O3 and 2006 PM2.5 standards. The variability in model predictions at different grid resolutions contributes to 1–3.8 ppb and 1–7.9 μg m−3 differences in the projected future-year design values for max 8-h O3 and 24-h average PM2.5, respectively.
Keywords: MM5/CMAQ; Impact of emissions on future air quality; Air quality standard attainment; Sensitivity to horizontal grid resolution;

Correlation of methane emissions with cattle population in Argentine Pampas by A. Huarte; V. Cifuentes; R. Gratton; A. Clausse (2780-2786).
Satellite cartography of atmospheric methane concentrations during 2003–2004 is applied to a systematic top-down methodology to quantify large scale sources and sinks of this important greenhouse gas. Patterns of methane anomalies over South America below latitude 22 S and an assessment of the emissions from the Buenos Aires Province of Argentina are reported. The latter contains the main cattle livestock of the country together with a variety of surface conditions, both natural and man-modified, influencing methane emissions. It was found that anomalies in methane concentrations may be correlated to emission rates by a simple box accumulation-sweeping model validated by recurrent weather conditions. The model shows that the methane emission rates of the Buenos Aires Province are positively correlated with the cattle livestock corresponding to values of (190 ± 40) g d−1 per cattle head.
Keywords: Methane inventory; Satellite cartography; Spatial analysis; Top-down methodology; Argentine cattle livestock;

The aim of this work is to quantify the sensitivity of shortwave radiative fluxes to changes in the vertical distribution of aerosol absorption, taken into account through the aerosol Single Scattering Albedo (SSA). The case study represents a real atmospheric situation with a desert dust layer (DDL) in the mid troposphere over an urban Boundary Layer (BL) observed at Rome on 20 June 2007. A moderately high aerosol optical depth (AOD), 0.292 at 550 nm, and low Ångström exponent of 0.30 were measured. The observed case was reconstructed with a radiative transfer model, in which the SSA of the boundary layer aerosols was varied from that of a highly absorbing aerosol type (urban) to a highly scattering one (clear marine). The SSA of the DDL is determined keeping fixed the measured SSA of the whole atmospheric column. The simulations show notable changes in the surface and top of the atmosphere (TOA) diffuse fluxes depending on the boundary layer aerosol properties. The aerosol radiative forcing (ARF) at the surface changes by 6–19 W m−2, depending on the solar zenith angle, when urban or clean marine particles are included in the boundary layer. The ARF differences observed at TOA are between 1 and 5 W m−2 when urban and clean marine aerosol types in the BL are respectively used, showing a smaller dependency on the solar zenith angle than at the surface.
Keywords: Aerosol single scattering albedo; Aerosol radiative forcing; Vertical profile;