Atmospheric Environment (v.40, #28)

Modeling the impacts of emission events on ozone formation in Houston, Texas by Junsang Nam; Yosuke Kimura; William Vizuete; Cynthia Murphy; David T. Allen (5329-5341).
The Houston/Galveston region has a large number of industrial point sources of volatile organic compounds (VOCs) and NO x , and observational data have shown that high concentrations of ozone are formed rapidly in the plumes of these industrial facilities. Some of the highly reactive VOC emissions from these facilities can be episodic, so in this work, photochemical air quality models, capable of simulating hundreds of possible types of emission events, have been developed and used to assess the impact of event magnitude, duration, timing and composition on ozone formation and accumulation. Simulations showed that ozone formation varied from nearly zero to up to 30 ppb per 1000 lb of release and that ozone formation depended strongly on the time of day of the release. The time of day that leads to maximum increases in ozone varies from day to day, depending on meteorology and NO x availability. On days and times that were conducive to ozone formation, the maximum additional ozone formation due to emission events was linearly related to emission magnitude, but the slope of that dependence varied based on the composition of the events. Overall, only a small percentage of emission events have the potential to lead to substantial ozone formation. Approximately 1.5% of emission events were projected to produce more than 10 ppb of additional ozone, and 0.5% of emission events were projected to produce more than 70 ppb of additional ozone, compared to base case simulations with no emission events.
Keywords: Photochemical Grid Model; Highly reactive volatile organic compounds (HRVOC); Ozone; Ethylene; Propylene;

The productivity responses of four barley (Hordeum vulgare L.) cultivars (Haider-93, Haider-91, Jou-87, Jou-85) to air pollution were investigated during 2004–2005 season using open-top chambers with charcoal-filtered air (FA), unfiltered air (UFA) and unchambered field plots (AA) at a semi-urban site in Lahore, Pakistan. The 8 h daily mean O3, NO2 and SO2 in UFA remained 71, 30 and 16 ppb, respectively. In UFA, seed yield was drastically reduced in all the cultivars, 13% for Haider-93, 30% for Haider-91, 34% for Jou-87 and 44% for Jou-85 compared with FA plants. This impact in UFA was due to combined effects of reductions in number of ears per plant, seeds per ear and 1000-seed weight. A mid-season harvest of 9-weeks-old plants has revealed 16–25% and 7–15% reductions in plant fresh and dry weights, respectively, in UFA compared with counterparts grown in FA. Plants grown in UFA also showed significant reductions in stomatal conductance (6–12%), transpiration rate (20–27%), net photosynthetic rate (13–21%) and photosynthetic efficiency (8–9%). Nutritional quality of seeds was, however, not altered with respect to some minerals (Ca, Mg, K, P), and protein in all treatments, except for higher starch contents found in FA than both UFA and AA treatments. The yield losses attributable to the mix of pollutants and experienced in the urban fringe of Lahore are appreciably larger than expected. Their significance more widely in Pakistan needs to be assessed as a matter of priority, as population growth rates and emission levels are both rapidly increasing in the country.
Keywords: Air pollution; Ozone; Yield; Photosynthesis; Open-top chamber; Nutritional quality; Pakistan;

Evolution of the urban aerosol during winter temperature inversion episodes by Sara Janhäll; K. Frans G. Olofson; Patrik U. Andersson; Jan B.C. Pettersson; Mattias Hallquist (5355-5366).
Winter temperature inversions are for Nordic urban sites a major cause for exceeding air-quality legislation thresholds for most primary pollutants. In this study, number particle size distributions have been measured and compared to other tracers for traffic emissions. Concentrations during winter days with and without morning temperature inversion were compared. Morning temperature inversion resulted in high concentrations of traffic-related pollutants, including CO, NO and NO2 together with ultrafine particles, while the pollution levels where considerably lower during mornings without temperature inversion. The specific time trends of NO x species could be well understood when considering the reaction with O3. The two different particle measures used in this study, i.e. the number concentration of ultrafine particles (10–100 nm) and the mass of particles below 10 μm (PM10), both increased during morning rush hours. When the morning inversion broke up and ground-level air mixed with air aloft, the number of particles decreased more rapidly than PM10 concentrations. LIDAR measurements were used to follow the vertical distribution of particles, and they clearly showed how the mixing processes started after the morning inversion and resulted in rising of the inversion followed by a relatively well-mixed boundary layer with a height of 1 km around 14:00.
Keywords: Winter inversion; Submicrometer particles; Traffic; Urban atmosphere; LIDAR;

Aerosol variability over Thessaloniki using ground based remote sensing observations and the TOMS aerosol index by M.E. Koukouli; D.S. Balis; V. Amiridis; S. Kazadzis; A. Bais; S. Nickovic; O. Torres (5367-5378).
The main aim of this work is to assess the performance of the Total Ozone Mapping Spectrometer (TOMS) on board the Earth Probe satellite aerosol index (AI) version 8.0 retrieved from the daily measurements of the TOMS instrument as an indicator of the presence of absorbing aerosols in the atmosphere. The analysis is carried out over the region of Northern Greece, an area exposed to various aerosol types from different sources. The aerosol optical depth (AOD) measured by a Brewer spectroradiometer situated in the centre of the city of Thessaloniki, at 40.6°N, 22.9°E, was employed as a measure of the aerosol loading in the atmosphere during the Earth Probe overpass. Discrete aerosol episodes that affect the area, such as biomass burning and Saharan dust events, have been isolated and studied in order to assess the effectiveness of using the TOMS AI in this highly complex atmospheric environment. The yearly values for the AOD measured at 355 nm range from 0.03 to 1.97 with a mean of 0.58±0.32 and for the AI from −1.67 to 3.06, with a mean of 0.22±0.73. This wide range of values results from the co-existence of urban, continental, marine and dust aerosols over Thessaloniki, a fact that makes it complicated to segregate optical effects on the observed radiation depending on different aerosol types. A total of 223 biomass burning events that affected Thessaloniki showed a correlation of 0.67 between the AOD and AI values whereas a correlation of 0.57 was deduced for the 37 cases of Saharan dust loading. A cluster analysis on the back-trajectories was performed in order to study the origins of the air masses over Thessaloniki, which permitted that the optical depth and AI were analysed depending on the possible source of the aerosols. The highest AOD values coupled with the highest AI values were seen for trajectories that transport air from the Saharan desert over Thessaloniki and those that bring polluted air from Eastern Europe and the Balkan regions. Even though some deductions were made vis-à-vis the origin and importance of different aerosol types over the city corroborating the usefulness of the AI in climatological or global climate studies, auxiliary information is essential for studying in detail the effects of the atmospheric aerosol loading over a local point of interest.
Keywords: Aerosol index; Aerosol optical depth; TOMS; Saharan dust; Brewer; Spectrometer;

Agricultural burning smoke in Eastern Washington: Part II. Exposure assessment by Chang-Fu Wu; Jorge Jimenez; Candis Claiborn; Tim Gould; Christopher D. Simpson; Tim Larson; L.-J. Sally Liu (5379-5392).
Several studies have documented potential health effects due to agricultural burning smoke. However, there is a paucity of literature characterizing community residents’ exposure to agricultural burning smoke. This study assesses personal exposures to particulate matter (PM) with aerodynamic diameters <2.5 μm (PM2.5) from agriculture burning smoke (E b) for 33 asthmatic adults in Pullman, WA. PM2.5 concentrations were measured on 16 subjects, inside of all but four residences, outside of 6 residences, and at a central site. The mean±standard deviation of personal exposure to PM2.5 was 13.8±11.1 μg m−3, which was on average 8.0 μg m−3 higher during the agricultural burning episodes (19.0±11.8 μg m−3) than non-episodes (11.0±9.7 μg m−3). The levoglucosan (LG, a unique marker for biomass burning PM) on personal filter samples also was higher during the episodes than non-episodes (0.026±0.030 vs. 0.010±0.012 μg m−3). We applied the random component superposition model on central-site and home indoor PM measurements, and estimated a central-site infiltration factor between 0.21 and 2.05 for residences with good modeling performance. We combined the source apportionment and total exposure modeling results to estimate individual E b, which ranged from 1.2 to 6.7 μg m−3 and correlated with personal LG with an r of 0.51. The sensitivity analysis of applying the infiltration efficiency estimated from the recursive model showed that the E b (range: 1.3–4.3 μg m−3) obtained from this approach have a higher correlation with personal LG ( r = 0.75 ). Nevertheless, the small sample size of personal LG measurements prevents a comparative and conclusive assessment of the model performance. We found a significant between-subject variation between episodes and non-episodes in both the E b estimates and subjects’ activity patterns. This suggests that the LG measurements at the central site may not always represent individual exposures to agricultural burning smoke. We recommend collecting more microenvironmental samples to model the E b and more personal samples to validate the E b estimates.
Keywords: Biomass burning; Smoke impact; Personal exposure; Random component superposition model; Recursive model; Spatial variation;

Lead isotope ratios in ambient aerosols from Taipei, Taiwan: Identifying long-range transport of airborne Pb from the Yangtze Delta by Shih-Chieh Hsu; Shaw Chen Liu; Woei-Lih Jeng; Charles C. K. Chou; Ru-Ting Hsu; Yi-Tang Huang; Yun-Wen Chen (5393-5404).
A total of 142 sets of PM10 and PM2.5 aerosol particles collected from Taipei during a period from April 2003 to February 2004 were determined for atmospheric Pb concentrations. Among these samples, 77 sets of samples representing four seasons were selected for measuring Pb isotopic compositions to determine the relative contributions of various pollution sources. Results reveal an evident seasonality of high winter and low summer Pb concentrations, resembling those observed in Shanghai, China as well as many East Asian countries. Together with synoptic atmospheric conditions analysis, the seasonal pattern is attributable to the impact of long-range transport of Pb-rich anthropogenic aerosols from the Chinese pollution outflows in the northeast monsoon and to the effective removal by wet deposition in summer. Results of 206Pb/207Pb and 208Pb/207Pb isotope ratios show a minimum in summer, thereafter increasing progressively to fall to winter and reaching a maximum in spring. The summer values are similar to that of tunnel particles for 206Pb/207Pb ratio but dissimilar to that of tunnel particles for 208Pb/207Pb ratio. Here summer aerosols may represent a local pollution-influenced case, and tunnel particles represent a vehicle exhaust source for atmospheric Pb. Therefore apart from vehicle emissions of Pb for Taipei aerosols, other sources such as incineration, metalliferous industry and coal combustion of fire power plants need to be taken into account. The winter and spring Pb isotope ratios are quite comparable with those measured in China, especially Shanghai in the Yangtze Delta. Again this demonstrates northern Taiwan has already been affected by continental pollution of long-range transport during the northeast monsoon season beginning in early fall and ending in late spring. By employing a two end-member mixing model based on the assumption that the summer case represents the local source end-member, the relative contributions of long-range transport for anthropogenic Pb have been estimated to be 40% in fall, 50% in winter, and 75–85% in spring.
Keywords: Lead isotope composition; Source apportionment; Asian pollution outflow; Cross-boundary transport; Shanghai;

The Regional Haze Rule of the US Environmental Protection Agency mandates reduction in US anthropogenic emissions to achieve linear improvement of visibility in wilderness areas over the 2004–18 period toward an endpoint of natural visibility conditions by 2064. Linear improvement is to apply to the mean visibility degradation on the statistically 20% worst days, measured as a Haze Index in units of deciviews (log of aerosol extinction). We use a global chemical transport model (GEOS-Chem) with 1°×1° horizontal resolution to simulate present-day visibility statistics in the USA, compare them to observations from the Interagency Monitoring of Protected Visual Environments (IMPROVE) surface network, and provide natural and background visibility statistics for application of the Regional Haze Rule. Background is defined by suppression of US anthropogenic emissions but allowance for present-day foreign emissions and associated import of pollution. Our model is highly successful at reproducing the observed variability of visibility statistics for present-day conditions, including the low tail of the frequency distribution that is most representative of natural or background conditions. We find considerable spatial and temporal variability in natural visibility over the USA, especially due to fires in the west. A major uncertainty in estimating natural visibility is the sensitivity of biogenic organic aerosol formation to the availability of preexisting anthropogenic aerosol. Background visibility is more variable than natural visibility and the 20% worst days show large contributions from Canadian and Mexican pollution. Asian pollution, while degrading mean background visibility, is relatively less important on the worst days. Recognizing the influence of uncontrollable transboundary pollution in the Regional Haze Rule would substantially decrease the schedule of emission reductions required in the 2004–18 implementation phase. Meaningful application of the Rule in the future will require projections of future trends in foreign anthropogenic emissions, wildfire frequency, and climate variables.
Keywords: Aerosols; Regional Haze Rule; Visibility degradation; Transboundary pollution transport; IMPROVE;

Plans to build a third runway at London Heathrow (LHR) airport have been held back because of concerns that the development would lead to annual mean concentrations of nitrogen dioxide (NO2) in excess of the EU Directive limit value, which must be met by 2010. The dominant effect of other sources of NO x close to the airport, primarily from road traffic, makes it difficult to detect and quantify the contribution made by the airport to local NO x and NO2 concentrations. This work presents approaches that aim to detect and quantify the airport contribution to NO x concentrations for a network of seven measurement sites close to the airport. Two principal approaches are used. First, a graphical technique using bivariate polar plots that develops the idea of a pollution rose is used to help discriminate between different source types. The sampling uncertainties associated with the technique have been calculated through a randomised re-sampling approach. Second, the unique pattern of aircraft activity at LHR enables data filtering techniques to be used to statistically verify the presence of aircraft sources. It is shown that aircraft NO x sources can be detected to at least 2.6 km from the airport, even though the airport contribution at that distance is very small. Using these approaches, estimates have been made of the airport contribution to long-term mean concentrations of NO x and NO2. At the airfield boundary we estimate that approximately 27% of the annual mean NO x and NO2 is due to airport operations. At background locations 2–3 km downwind of the airport we estimate that the upper limit of the airport contribution to be less than 15% (<10 μg m−3). This work also provides approaches that would help validate and refine dispersion modelling studies used for airport assessments.
Keywords: London; Urban air quality; Heathrow airport; Aircraft emissions; Source apportionment;

Atmospheric concentrations of trace metals over the oceans are investigated through analysis of aerosol samples collected during cruises from the UK to the Falkland Islands and from South Africa to Australia. The readily soluble concentrations of Cu (4–256 pmol m−3), Ni (0.1–54 pmol m−3), Ba (0.2–60 pmol m−3), Zn (6–316 pmol m−3), Cd (0.01–0.29 pmol m−3) and Pb (0.4–22 pmol m−3) were measured in the aerosols, along with total concentrations of crustal elements (Fe, Al and Mn) to evaluate the crustal contributions. Air mass back trajectories suggested most of the aerosol samples had spent several days over the ocean prior to collection. The highest metal concentrations were observed in aerosols close to South Africa, Australia and major cities in South America, although these concentrations were lower than had been reported previously in the literature. Apart from Ba, which had a major crustal source, the trace metals were enriched relative to crustal sources in most samples, including some collected thousands of kilometers from emission sources. The mean trace metal concentrations in the remote Indian Ocean were lower than those measured in the Atlantic Ocean. Even lower concentrations are reported in the literature for the remote Pacific Ocean. In contrast to previous studies, no clear north–south gradient is observed in the concentrations of the trace metals in the aerosols.Lead isotope measurements were also carried out on aerosol samples using a multicollector inductively coupled plasma mass spectrometer to assist in source apportionment. Clear differences were noted in the isotope ratios collected on either side of the Indian Ocean with Australian lead ore dominating over much of the eastern and mid-southern Indian Ocean. Samples collected over the western Indian Ocean and Atlantic Ocean under South African influence had lead isotopes quite different from those seen in South African cities in the past, and are closer in ratio to the coal signature of the region.
Keywords: Pb; Isotope signature; Enrichment factor; Aerosols; Trajectories;

Fluxes of reactive gaseous mercury measured with a newly developed method using relaxed eddy accumulation by Henrik Skov; Steven B. Brooks; Michael E. Goodsite; Steve E. Lindberg; Tilden P. Meyers; Matthew S. Landis; Michael R.B. Larsen; Bjarne Jensen; Glen McConville; Jesper Christensen (5452-5463).
There is a qualitative understanding that gaseous elemental mercury (GEM) is oxidized during Arctic spring to reactive gaseous mercury (RGM) that afterwards is removed by fast deposition to snow surfaces.The conditional sampling or relaxed eddy accumulation (REA), technique represents the first opportunity to directly measure fluxes of reactive gaseous mercury (RGM) to the snow pack in the Arctic. Using a micrometeorological method REA system, with a heated sampling system specifically designed for Arctic use, the dry deposition of RGM is measured after polar sunrise, in Barrow, Alaska. Heated KCl-coated manual RGM annular denuders were used as the accumulators with an inlet allowing only fine particles to pass (Cut off diameter 2.5 μm). At 3 m above the snow pack significant RGM fluxes were measured each spring in 2001–2004. Both depositions and emissions were observed. The emissions were attributed to chemical formation of RGM at or near the snow surface. The surface resistance, R c, for RGM was found to be very small and set to zero as a first estimate.
Keywords: Arctic; Atmospheric mercury depletion episodes; Conditional sampling; Deposition; Reactive gaseous mercury; Emission; Micrometeorology; Snow–air exchange;

Examination of pollution trends in Santiago de Chile with cluster analysis of PM10 and Ozone data by E. Gramsch; F. Cereceda-Balic; P. Oyola; D. von Baer (5464-5475).
Because of the high levels of pollution that Santiago de Chile experiences every year in winter, the government has set up an air quality monitoring network. Information from this network is employed to alert people about the quality of air and to enforce several control strategies in order to limit pollution levels. The monitoring network has 8 stations that measure PM10, carbon monoxide (CO), sulphur dioxide (SO2), ozone (O3) and meteorological parameters. Some stations also measure nitrogen mono- and dioxide (NO x ), fine particles (PM2.5) and carbon. In this study we have examined the PM10 and O3 data generated by this network in the year 2000 in order to determine the seasonal trends and spatial distribution of these pollutants over a year's period. The results show that concentration levels vary with the season, with PM10 being higher in winter and O3 in summer. All but one station, show a peak in PM10 at 8:00 indicating that during the rush hour there is a strong influence from traffic, however, this influence is not seen during the rest of the day. In winter, the PM10 maximum occurs at 24:00 h in all stations but Las Condes. This maximum is related to decreased wind speed and lower altitude of the inversion layer. The fact that Las Condes station is at a higher altitude than the others and it does not show the PM10 increase at night, suggest that the height of the inversion layer occurs at lower altitude. Cluster analysis was applied to the PM10 and O3 data, and the results indicate that the city has four large sectors with similar pollution behavior. The fact that both pollutants have similar distribution is a strong indication that the concentration levels are primarily determined by the topographical and meteorological characteristics of the area and that pollution generated over the city is redistributed in four large areas that have similar meteorological and topographical conditions.
Keywords: Particulate matter; Ozone; Cluster analysis;

Uptake of gaseous aromatic hydrocarbons by non-growing ice crystals by Elke Fries; Werner Haunold; Wolfgang Jaeschke; Ines Hoog; Subir K. Mitra; Stephan Borrmann (5476-5485).
Laboratory studies were performed in a walk-in cold chamber to investigate the uptake of aromatic hydrocarbons by non-growing ice crystals at −20 °C. Dendritic ice crystals were grown by vapor deposition and exposed to organic gases (benzene, toluene, ethylbenzene, m/p-xylene, o-xylene, n-propylbenzene, 4-ethyltoluene, 1,3,5-trimethylbenzene, tert-butylbenzene, 1,2,4-trimethylbenzene, and 1,2,3-trimethylbenzene) at gas-phase concentrations between 2.8 and 33.1 μg m−3. During all exposure experiments, the gas/air stream was maintained at ice saturation to avoid ice crystal growth or evaporation. An analytical method comprising of solid-phase-micro-extraction followed by gas chromatography/mass spectrometry (SPME/GC–MS) was applied, which allows detection of organic compounds in melted ice at 0.025 ng gice −1. The SPME/GC–MS method was an appropriate tool to determine the uptake of organic compounds by ice crystals at the applied gas-phase concentrations. However, it was not possible to detect any of the test substances in ice samples after exposure. No adsorption could be detected by increasing gas-phase concentrations. Neither increasing exposure time nor lowering flow rate of the carrier gas caused detectable adsorption effects of aromatic compounds on ice. Our results indicate that adsorption of aromatic hydrocarbons is either insignificant or highly reversible at −20 °C. These findings are consistent with reversible adsorption processes reported already for many oxygenated organic compounds like alcohols, acids, and aldehydes. Although the specific surface area of dendritic ice crystals is large, the results of our study demonstrate that gas uptake by ice surfaces is negligible for the removal of aromatic hydrocarbons in the atmosphere. This is an indication that the occurrence of aromatic hydrocarbons in precipitation cannot be explained by surface adsorption. There must be another accumulation process leading to concentrations of aromatic hydrocarbons found in field studies which is still unknown.
Keywords: Aromatic hydrocarbons; Ice crystals; Uptake; SPME; Adsorption;

Atmospheric isoprene and other selected hydrocarbons were measured continuously at a suburban site and an urban site in order to study their possible effects on ozone formation in different seasons. The summer measurements at both the urban and suburban sites revealed that atmospheric mixing ratios of isoprene were synchronous with solar radiation, concentrations reaching a maximum at noon and decreasing to near zero in the evening. In contrast, wintertime atmospheric abundance of isoprene showed little concurrency with solar radiation. As the biogenic source subsided in winter, the anthropogenic source started to play a dominant role in controlling the atmospheric abundance of isoprene. Using propane as a reference compound, the source characteristics of isoprene were able to be deconvoluted from meteorological modulation confirming the insignificant biogenic contribution in winter.Implication of isoprene on noontime ozone formation was discussed not only from the aspect of reactivity but also from the time characteristics of the diurnal cycle. This study demonstrates that although the reactivity is important, the timing of the flux, which has been shown to have drastic difference between the cold and warm seasons, could play an even more critical role in shaping the daily ozone profile. This investigation shows that the midday emissions of isoprene in warm seasons could produce a much larger photochemical loss and therefore, a stronger ozone formation ability than emitted in other hours of a day due to the coherence of isoprene and OH diurnal cycles, both of which are sunlight driven.
Keywords: Ozone precursors; Isoprene; Volatile organic compounds (VOCs); Automated GC;

Environmental control of profiles of ozone concentration in a grassland canopy by M. Jäggi; C. Ammann; A. Neftel; J. Fuhrer (5496-5507).
In multi-species grassland communities, ozone exposure of individual species may differ due to their location inside the canopy. In this study, it was tested how the ozone profile inside a grassland canopy is influenced by the vertical distribution of leaf area (LAI) and by meteorological parameters, specifically by the turbulence intensity quantified by the friction velocity (u *). Multi-level ozone profiles were measured continuously during the first growth period of intensively managed grassland, and stomatal conductance (g s) was measured in the two dominant species, i.e. white clover (Trifolium repens) at 0.25 m and meadow foxtail (Alopecurus pratensis) at 0.50 m. In the two-layer structure of the canopy, with <20% of LAI located in the upper half, radiation (PAR) was only moderately reduced throughout the canopy thus favouring high g s also in the lower part. Daytime ozone concentration at 0.25 m, where white clover was dominant, was reduced on average by 36% of the value at the reference height of 0.90 m. When scaled with canopy height, this reduction was considerably larger than most comparable published data for other vegetation types. The shape of the ozone profile in the canopy was not affected by increasing LAI from 4.7 to 6.8 m2  m−2 or by the changing vertical distribution of LAI during the observation period. The main environmental influence on the shape of the profile could be attributed to u *. Generally, relative in-canopy concentrations of ozone increased with u *. This could explain the stronger and more variable ozone depletion during nighttimes. The different levels of ozone exposure of species predominantly located in the upper and lower parts of the canopy supports a multi-layer approach to modelling uptake of ozone, which is important for the assessment of ozone risks for individual plants growing in grasslands.
Keywords: Grass–clover mixture; In-canopy profiles; LAI distribution; Stomatal conductance; Turbulence intensity;

Air quality impacts of distributed power generation in the South Coast Air Basin of California 1: Scenario development and modeling analysis by M.A. Rodriguez; M. Carreras-Sospedra; M. Medrano; J. Brouwer; G.S. Samuelsen; D. Dabdub (5508-5521).
Distributed generation (DG) is generally defined as the operation of many small stationary power generators throughout an urban air basin. Although DG has the potential to supply a significant portion of the increased power demands in California and the rest of the United States, it may lead to increased levels of in-basin pollutants and adversely impact urban air quality. This study focuses on two main objectives: (1) the systematic characterization of DG installation in urban air basins, and (2) the simulation of potential air quality impacts using a state-of-the-art three-dimensional computational model. A general and systematic approach is devised to construct five realistic and 21 spanning scenarios of DG implementation in the South Coast Air Basin (SoCAB) of California. Realistic scenarios reflect an anticipated level of DG deployment in the SoCAB by the year 2010. Spanning scenarios are developed to determine the potential impacts of unexpected outcomes. Realistic implementations of DG in the SoCAB result in small differences in ozone and particulate matter concentrations in the basin compared to the baseline simulations. The baseline accounts for population increase, but does not consider any future emissions control measures. Model results for spanning implementations with extra high DG market penetration show that domain-wide ozone peak concentrations increase significantly. Also, air quality impacts of spanning implementations when DG operate during a 6-h period are larger than when the same amount of emissions are introduced during a 24-h period.
Keywords: Distributed power generation; Air quality modeling; Ozone; PM2.5; South Coast Air Basin of California;

Littoral zones as the “hotspots” of nitrous oxide (N2O) emission in a hyper-eutrophic lake in China by Hongjun Wang; Weidong Wang; Chengqing Yin; Yuchun Wang; Jinwei Lu (5522-5527).
N2O emissions were measured monthly for 1 year using the static chamber method along the littoral and pelagic zones of Meiliang Bay in hyper-eutrophic Taihu Lake. The results indicated that littoral zones were the “hotspots” of N2O emissions (−278∼2 101 μg N2O m−2  h−1). While the littoral zone accounted for only 5.4% of the area of Meiliang Bay, the N2O emissions from the littoral zones were about 43.6% of total emissions from the bay. The importance of spatial variation on N2O emissions was demonstrated by dividing the lake into four unique zones through cluster analysis. The eulittoral zone was the key area of N2O emissions with an annual 5% trimmed mean 429.5 μg N2O m−2  h−1, following by supralittoral (138.8 μg N2O m−2  h−1), infralittoral (98.9 μg N2O m−2  h−1), and pelagic zones (15.7 μg N2O m−2  h−1). Further, N2O emissions showed a seasonal trend. Excessive N2O emissions during algal bloom periods suggested that algae played a significant role in the emission of N2O.
Keywords: Lakeshore; Greenhouse gas; Trace gas; Denitrification; Aquatic system;

Methane emission patches in riparian marshes of the inner Mongolia by Zhi-Ping Wang; Xing-Guo Han; Ling-Hao Li (5528-5532).
Natural wetlands are an important methane (CH4) source. However, emission inventories of them are rather uncertain. One reason for this is the existence of ubiquitous wetland patches. Using a static-chamber technique, we performed field measurements in the inner Mongolia marshes to compare the CH4 fluxes between a sandy marsh and an organic marsh, and between a patch and the vicinity, and determine the seasonal variation of CH4 fluxes. For each marsh, the CH4 flux in the patch was significantly higher than that in the vicinity. Both marshes presented the similar patch pattern of CH4 emissions. Another remarkable result was the very high CH4 fluxes in the organic marsh, which averaged 1817.3 and 517.4 mg CH4  m−2  d−1 in the patch and the vicinity, respectively, during July–September 2004. The very high fluxes mainly resulted from the dense plants. It could be proposed that CH4 emission patches need to be accounted for in developing an accurate estimate of the global source strength of wetlands.
Keywords: CH4 flux; Heterogeneity; Hot spots; Wetland; Xilin River basin;