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Atmospheric Environment (v.42, #18)

Editorial board (pp. i).

Experimental evaluation of hybrid vehicle fuel economy and pollutant emissions over real-world simulation driving cycles by Georgios Fontaras; Panayotis Pistikopoulos; Zissis Samaras (pp. 4023-4035).

The reduction of transport-generated CO₂ emissions is currently a problem of global interest. Hybrid electric vehicles (HEVs) are considered as one promising technological solution for limiting transport-generated greenhouse gas emissions. Currently, the number of HEVs in the market remains limited, but this picture will change in the years to come as HEVs are expected to pave the way for cleaner technologies in transport. In this paper, results are presented regarding fuel economy and pollutant emissions measurements of two hybrid electric production vehicles. The measurements were conducted on a Prius II and a Honda Civic IMA using both the European legislated driving cycle (New European Driving Cycle, NEDC) and real-world simulation driving cycles (Artemis). In addition to the emissions measurements, other vehicle-operating parameters were studied in an effort to better quantify the maximum CO₂ reduction potential. Data from real-world operation of a Prius II vehicle were also used in the evaluation. Results indicate that in most cases both vehicles present improved energy efficiency and pollutant emissions compared to conventional cars. The fuel economy benefit of the two HEVs peaked under urban driving conditions where reductions of 60% and 40% were observed, respectively. Over higher speeds the difference in fuel economy was lower, reaching that of conventional diesel at 95kmh⁻¹. The effect of ambient temperature on fuel consumption was also quantified. It is concluded that urban operation benefits the most of hybrid technology, leading to important fuel savings and urban air quality improvement.

Keywords: Hybrid electric vehicles; Fuel consumption; Vehicle emissions; Artemis

Correlation of aerosol mass near the ground with aerosol optical depth during two seasons in Munich by Schafer Klaus Schäfer; Andreas Harbusch; Stefan Emeis; Peter Koepke; Matthias Wiegner (pp. 4036-4046).

Relations of the aerosol optical depth (AOD) with aerosol mass concentration near the ground, particulate matter (PM), have been studied on the basis of measurements. The objective is with respect to possible remote sensing methods to get information on the spatial and temporal variation of aerosols which is important for human health effects. Worldwide the AOD of the atmospheric column is routinely monitored by sun-photometers and accessible from satellite measurements also. It is implied here that the AOD is caused mainly by attenuation processes within the mixing layer because this layer includes nearly all atmospheric aerosols. Thus the mixing layer height (MLH) is required together with the AOD, measured by ground-based sun-photometers (around 560nm), to get information about aerosols near the ground. MLH is determined here from surface-based remote sensing. Investigations were performed during two measurement campaigns in and near Munich in May and November/December 2003 on the basis of daily mean values. Using AOD and MLH measurements the aerosol extinction coefficient of the mixing layer has been calculated. This quantity was correlated with the measured PM₁₀, PM_2.5 and PM₁ mass concentrations near the ground by performing a linear regression and thus providing a mass extinction efficiency giving squares of the correlation coefficients ( R²) between 0.48 (PM₁ during summer campaign) and 0.90 (PM_2.5 during winter campaign). These correlations suggest that the derived mass extinction efficiencies represent a statistically significant relation between the aerosol extinction coefficients and the surface-based PM mass concentrations mainly during winter conditions.

Keywords: Optical depth; Air pollution; Particulate matter; Mixing layer height

Spatio-temporal modeling of chronic PM₁₀ exposure for the Nurses’ Health Study by Jeff D. Yanosky; Christopher J. Paciorek; Joel Schwartz; Francine Laden; Robin Puett; Helen H. Suh (pp. 4047-4062).

Chronic epidemiological studies of airborne particulate matter (PM) have typically characterized the chronic PM exposures of their study populations using city- or county-wide ambient concentrations, which limit the studies to areas where nearby monitoring data are available and which ignore within-city spatial gradients in ambient PM concentrations. To provide more spatially refined and precise chronic exposure measures, we used a Geographic Information System (GIS)-based spatial smoothing model to predict monthly outdoor PM₁₀ concentrations in the northeastern and midwestern United States. This model included monthly smooth spatial terms and smooth regression terms of GIS-derived and meteorological predictors. Using cross-validation and other pre-specified selection criteria, terms for distance to road by road class, urban land use, block group and county population density, point- and area-source PM₁₀ emissions, elevation, wind speed, and precipitation were found to be important determinants of PM₁₀ concentrations and were included in the final model. Final model performance was strong (cross-validation R²=0.62), with little bias (−0.4μgm⁻³) and high precision (6.4μgm⁻³). The final model (with monthly spatial terms) performed better than a model with seasonal spatial terms (cross-validation R²=0.54). The addition of GIS-derived and meteorological predictors improved predictive performance over spatial smoothing (cross-validation R²=0.51) or inverse distance weighted interpolation (cross-validation R²=0.29) methods alone and increased the spatial resolution of predictions. The model performed well in both rural and urban areas, across seasons, and across the entire time period. The strong model performance demonstrates its suitability as a means to estimate individual-specific chronic PM₁₀ exposures for large populations.

Keywords: Air pollution; Particulate matter; Geographic Information System; Spatial smoothing; Generalized additive modelsAbbreviations; AQS; air quality system; CFCC; Census Feature Class Code; ESRI; Environmental Systems Research Institute; GAM; generalized additive model; GIS; Geographic Information System; IDW; inverse distance weighting; IMPROVE; Interagency Monitoring of Protected Visual Environments; km; kilometer; NCDC; National Climatic Data Center; NLCD; National Land Cover Data Set; NEI; National Emissions Inventory; NED; National Elevation Data Set; PM; particulate matter; PM; ₁₀; mass concentration of airborne inhalable particles (aerodynamic diameter<10; μm); RMSPE; square root of the mean of the squared prediction errors; SLBP; sea-level adjusted barometric pressure; US; United States; USEPA; US Environmental Protection Agency; USGS; US Geological Survey; VIEWS; Visibility Information Exchange Web System

Mass size distributions of water-soluble inorganic and organic ions in size-segregated aerosols over metropolitan Newark in the US east coast by Yunliang Zhao; Yuan Gao (pp. 4063-4078).

To characterize the mass size distributions of water-soluble inorganic and organic ions associated with urban particulate matter, a total of 15 sets of size-segregated aerosol samples were collected by a 10-stage Micro-Orifice Uniform Deposit Impactor (MOUDI) in the urban area of Newark in New Jersey from July to December 2006. The mass concentrations of PM_1.8 accounted for ∼68% of the mass concentrations of PM₁₀. The mass concentrations of the total water-soluble ions in PM_1.8 accounted for 31–81% of the mass concentrations of PM_1.8. Sulfate was the dominant ion in fine particles, accounting for 31% of the PM_1.8 mass with its dominant mode at 0.32–0.56μm throughout all the samples. Nitrate size distributions were bi-modal, peaking at 0.32–0.56 and 3.2–5.6μm, and the shift of the nitrate dominant fraction between fine and coarse modes was affected by temperature. The ratios of nitrate to PM_1.8 varied significantly, 0.5–27%. The C2–C4 dicarboxylic acids accounted for 1.9±0.9% of PM_1.8 mass, with oxalate being the dominant ion. The size distributions of oxalate exhibited two to four modes with the dominant one at 0.32–0.56μm. Chloride existed in both coarse and fine modes, suggesting the influence of sea-salt aerosol and anthropogenic emissions. A crucial formation mechanism for the mass size distributions of these ions observed at this location is likely to be a combination of the gas-to-particle conversion and in-cloud/fog processing.

Keywords: Mass size distributions; Sulfate; Nitrate; Dicarboxylic acids; Urban aerosols

Development of highly sensitive passive sampler for nitrogen dioxide using porous polyethylene membrane filter as turbulence limiting diffuser by Yoshika Sekine; Simon F. Watts; Andrew Rendell; Michio Butsugan (pp. 4079-4088).

A new design of passive sampler is described which is appropriate to reduce the sampling resolution of most formats of Palmes’ tubes from weeks to 24h or less. The sampler employs a flat-type porous polyethylene membrane filter as a diffuser, which controls mass transfer of the target analyte from ambient air to impregnated trapping filter. The new design is applicable to any analyte for which there is a paper Palmes’ tube method, e.g. H₂S, OCS, NO, SO₂, O₃, organic acids, NH₃ and so on. As an example, the sampler for the determination of ambient atmospheric nitrogen dioxide (NO₂), employing a trapping filter impregnated with triethanolamine is described. Performance of the new sampler was evaluated in laboratory and field experiments. The sampling rate was measured directly at four kerb-side sites in Oxford, UK and Kanagawa, Japan, by comparing measured concentrations from the samplers with co-located automated NO₂ analyzers. Results showed mass transfer rate of NO₂ within the diffuser did not change with external wind speed (0.5–2ms⁻¹). The passive device had relatively higher sampling rate than those of previous samplers and gave equivalent results on NO₂ concentrations to the automated NO₂ analyzer at 24h or less sampling duration. LOD and LOQ indicated possible application of these devices to sampling in urban intermediate, urban background and suburban areas.

Keywords: Passive sampler; Diffusion filter; Nitrogen dioxide; Turbulence; Sampling rate; Palmes’ tube

Carbonaceous aerosols in MABL of Bay of Bengal: Influence of continental outflow by A.K. Sudheer; M.M. Sarin (pp. 4089-4100).

Elemental carbon (EC) and organic carbon (OC) concentrations along with the total suspended particulate matter (TSP) have been measured in the marine atmospheric boundary layer (MABL) of Bay of Bengal (BoB) during the spring inter-monsoon season (19 March–11 April 2006). The abundance of EC (range: 0.12–0.66μgm⁻³; Av: 0.4μgm⁻³) is found to be only ∼2% of TSP, whereas particulate organic matter (calculated based on OC ranging from 0.3 to 5.5μgm⁻³, Av. 1.9μgm⁻³) contributes nearly 11% of the average TSP (22μgm⁻³). The spatial distribution of carbonaceous species shows a higher concentration in the northern Bay and decreases towards the central and south-eastern region suggesting the advective transport of continental pollutants to the MABL. The influence of anthropogenic sources is further supported by the elevated levels of nss-SO42- (4.7–11μgm⁻³) in the northern region. A comparison with the data collected during February 2003 (late NE-monsoon) from the same region consistently demonstrates a similar feature of the continental outflow, but a factor of 2–3 higher concentrations of carbonaceous species (EC: 0.4–3.4μgm⁻³; OC: 2–8μgm⁻³). OC/EC ratios were 6.5 and 7.4 for sampling seasons in 2003 and 2006 and for nss-SO42-/EC ratios were 6 and 15 respectively. The significantly higher abundances of EC during late NE-monsoon (February) demonstrate the strong influence of polluted air masses in the MABL decreasing rapidly with the shift in the wind regimes (March–April).

Keywords: Organic carbon; Elemental carbon; OC/EC ratio

The influence of photocatalytic interior paints on indoor air quality by Joonas Auvinen; Leif Wirtanen (pp. 4101-4112).

A clean indoor air is important for the well-being and health of people. Lately, new photocatalytic paints have been launched on the market, which are claimed to have air-purifying effects. Photocatalysis initiates radical reactions. Radicals are formed when a photocatalyst (e.g. TiO₂^{) is subjected to radiation. Typical radicals are the hydroxyl radical (}^{OH) and the superoxide radical (}O₂⁻). Radicals cause chain reactions, which degrade and decompose organic compounds. The end products of these chain reactions are water and carbon dioxide, if the reactions are fully completed (mineralization). If mineralization does not take place, then a great number of side products can be formed, whose properties are not well understood. The side products of photocatalytic reactions can be permanent and stabile. The decomposition of indoor air impurities on the surface of photocatalytic paints is not obvious. The ability of photocatalytic indoor paints to reduce chemical indoor air impurities is the key issue of this study. Six different paints with different binder systems, such as lime, polyorganic siloxane, silica sol–gel and organic binders, were examined. The experiments were divided into three topics: degradation of an organic binder, photocatalytic decomposition of formaldehyde, and a volatile organic compound (VOC) mixture consisting of five different indoor air VOCs. All tests were carried out in an environmental test chamber under dynamic conditions. The test results indicate that many indoor pollutants are generated under normal- and UVA-light. Typical compounds formed include formaldehyde, acetone, acetaldehyde, etc. A clear decrease of formaldehyde or the VOC mixture concentration was not observed. All possibly generated compounds could not be collected or analyzed in this research project, but the measurements show that photocatalytic reactions do not generate only carbon dioxide and water. Photocatalytic decomposition of indoor air impurities can, however, produce many side products, which may be stabile and harmful.

Keywords: VOC; Formaldehyde; Photocatalysis; Interior paints; TiO; ₂

Diurnal variation of atmospheric aerosol during the wood combustion season in Northern Sweden by Patricia Krecl; Strom Johan Ström; Christer Johansson (pp. 4113-4125).

A set of aerosol measurements was conducted in the residential area of Forsdala in Lycksele, Northern Sweden, during winter 2005/2006. This article describes the temporal and diurnal variation of the aerosol physical properties (concentrations of PM₁₀, PM₁, light-absorbing carbon, and particle number, and number size distributions), and the relationship among aerosol concentrations and meteorological variables. A large day-to-day and hour-to-hour variability in aerosol concentrations was observed during the intensive study period. Evening aerosol concentrations were statistically significantly higher on weekends than on weekdays. On weekdays, particle size distribution and concentrations varied diurnally with small particles (diameter <30nm) associated mainly with morning motor vehicle emissions. The results suggest that a combination of emissions from residential wood combustion and traffic sources might explain the high evening concentrations of PM₁₀, PM₁, particle number, and light-absorbing carbon as well as large geometric mean diameters observed during weekdays and weekends. Strong correlations of PM₁₀ and PM₁ with particle size distributions are found in the diameter range 130–500nm and are remarkably high on weekend evenings when larger particles are sampled. The correlation between light-absorbing carbon mass concentration and particle size distribution is high regarding both particle number and mass for particle diameters >95nm. High aerosol concentrations were associated with low air temperatures and very stable atmospheric conditions close to the ground.

Keywords: Residential wood combustion; Black carbon; Particle size distribution; PM; ₁₀; PM; ₁

Source apportionment of PM_2.5: Comparing PMF and CMB results for four ambient monitoring sites in the southeastern United States by Sangil Lee; Wei Liu; Yuhang Wang; Armistead G. Russell; Eric S. Edgerton (pp. 4126-4137).

Two commonly used receptor models, positive matrix factorization (PMF) and chemical mass balance (CMB), are applied to 3-year PM_2.5 data at two urban sites (Atlanta, GA and Birmingham, AL) and two rural sites (Yorkville, GA and Centreville, AL). Source apportionment results using the two receptor models are analyzed and compared. Both models are able to identify major sources at all sites, though the degree of agreements and correlations between source impacts estimated by PMF and CMB varies depending on sources and receptor sites. Estimated contributions of secondary inorganic particles are the most comparable and highly correlated. The lesser comparability and correlations of estimated contributions of other sources (mostly primary) may be attributed to several factors. Resolved source profiles in PMF have more processed (or aged) characteristics resulting in part from atmospheric mixing and condensation of oxidized compounds, whereas source profiles used in CMB are obtained from measurements of emission sources with minimum amount of atmospheric processing. The PMF profiles vary from site to site; both atmospheric processing and local source variability contribute. In comparison, the CMB profiles obtained from a limited number of emission measurements may not be locally representative even if they are regionally representative. The omission of possible known or unknown sources due to lack of proper source profiles or proper “marker” species may also cause the differences in the source apportionment results. In addition, the implication for PM time-series health study is discussed based on the results from this study.

Keywords: PMF; CMB; Source apportionment; PM; _2.5; Time-series health study

Ten-year measurements of gaseous pollutants in urban air by an open-path analyzer by P. Avino; M. Manigrasso (pp. 4138-4148).

Object of this study is the versatility of a remote-sensing measurement system through experimental survey of the levels of primary and secondary pollutants in urban areas. For the first time a long-range measurement of different pollutant for a long period are reported in the urban area of Rome. Over 10 years of data collection, levels of NO₂, O₃, SO₂, benzene and toluene are measured and discussed by means of a differential optical absorption spectroscopy (DOAS) system installed at ground level.The period is interesting because it represents one of the most important life-changes in Europe and in Italy: in fact, during the 1990s some significant decrees introduced the catalytic pots and limited the amount of benzene and sulfur dioxide in the fuel. The paper will describe how the main primary and secondary pollutants are changed during all the period: particularly, benzene and SO₂ are not over a big social problem for the human health whereas the secondary pollutants, ozone and nitrogen dioxide, have the same trends during the period, meaning a no contribution to their evolution from the atmospheric processes.The DOAS technique is resulted very useful and versatile: comparisons with other traditional analyzers (i.e., GC-PID for benzene and toluene investigations) demonstrate how it allows to have information over all the territory saving the qualitative trends and giving a similar quantitative result. In this respect the authors show that the difference is due to the different sampling ways (the traditional analyzers are punctual whereas the DOAS is a remote-sensing technique covering a wide area) and does not influence the atmospheric process interpretation.Finally, it should be considered that the pollutant trends have been interpreted using the concentration measurements of natural radioactivity as tracer of the dynamic properties of the atmospheric boundary layer.

Keywords: DOAS; Air pollution; Primary pollutant; Radon; Photochemical smog

Ultrafine particles produced by ozone/limonene reactions in indoor air under low/closed ventilation conditions by Sarka Langer; Moldanova Jana Moldanová; Karine Arrhenius; Ljungstrom Evert Ljungström; Lars Ekberg (pp. 4149-4159).

Formation of ultrafine particles, d_p<100nm, from gas-phase reaction of limonene with O₃ was studied. The concentration of reactants was chosen as close to realistic indoor conditions as possible. Two reaction chambers (1 and 14m³) were used. Particle number concentrations were measured using a CPC and size distributions by using a scanning mobility particle sizer (SMPS) system. Rapid formation of new particles was observed at low concentrations of reactants and close to zero ventilation rates. The maximum number of particles was correlated with the initial rate of formation of reaction products. An excess of O₃ tends to give higher maximum particle concentrations. Modeling work lead to the conclusion that significant nucleation starts when the mixing ratio of “product” from the reaction Limonene+O₃→product_ox exceeds 0.5–1ppb. The secondary particles formed by atmospheric chemistry in indoor air contribute to the total particulate matter indoors and should be considered in terms of low-dose long-term exposure.

Keywords: Indoor air chemistry; Ozone; Limonene; Ultrafine particles; Secondary organic aerosol

Effects of elevated CO₂ and temperature on monoterpene emission of Scots pine ( Pinus sylvestris L.) by Raisanen Tommi Räisänen; Ryyppo Aija Ryyppö; Kellomaki Seppo Kellomäki (pp. 4160-4171).

The aim of this study was to evaluate the long-term (5 years) effects of elevated CO₂ concentration (doubling of ambient CO₂ concentration) and temperature (2–6°C elevation) on the monoterpene emission of Scots pine ( Pinus sylvestris L.) saplings (ca. 20 years old) grown in closed-top environmental chambers. The chamber treatments included: (1) ambient temperature and CO₂, (2) ambient temperature and elevated CO₂, (3) elevated temperature and ambient CO₂, and (4) elevated temperature and elevated CO₂. The variability of emissions during and after tree shoot growth was studied, and additionally the total cumulative emission of monoterpenes through a growing period (May–September) was estimated. When compared to the controls, the combination of elevated CO₂ and temperature significantly increased normalized monoterpene emission rate for the whole growing period (+23%), whereas elevated CO₂ had no significant effect (−4%), and elevated temperature even decreased (−41%) the emission rate. The increasing effect of the combination of elevated CO₂ and temperature was strongest during shoot growth (+54%). After shoot growth, no significant differences in emission rate were found among the treatments. Emission modeling showed that the total amount of monoterpenes emitted from May to September was 2.38mgg_dw⁻¹ in ambient conditions. The total emission in elevated CO₂ was 5% greater and in elevated temperature 9% lesser than in ambient conditions. The combination of elevated CO₂ and temperature increased the amount of emitted monoterpenes over the growing period by 126% compared to the total emission in ambient conditions.

Keywords: Elevated CO; ₂; and temperature; Monoterpene emission; Pinus sylvestris; Secondary compounds; VOC

Energy dynamics and its implication to biosphere–atmosphere exchange of CO₂, H₂O and CH₄ in a tropical mangrove forest canopy by D. Ganguly; M. Dey; S.K. Mandal; T.K. De; T.K. Jana (pp. 4172-4184).

Amount of radiant energy (short wave) available to drive biosphere–atmosphere exchange of CO₂, H₂O, CH₄ and for transfer into other energy forms were determined for a tropical mangrove forest at the land ocean boundary of north-east (NE) coast of Bay of Bengal from January to December 2006. The mean annual incoming short wave radiation (435±32.8Wm⁻²) was partitioned into 29% sensible heat, 35% latent heat, 4% ground heat, 7% physical storage energy and 10% photosynthetic storage energy. The mean budget closing energy flux (68.96±24.6Wm⁻²) or, budget error was 15.8% of incoming short wave radiation. In Varimax factor analysis, budget closing energy flux showed high loading in association with leaf chlorophyll of different mangrove species, indicating its major role for reflectivity of the surface for short wave. There was significant seasonality in CO₂ exchange with net primary productivity of 14.1μmolm⁻²s⁻¹. The mean methane emission was found higher (7.29μgm⁻²s⁻¹) during the daytime than that of night time (1.37μgm⁻²s⁻¹) with maximum methane emission rates of 36.1 and 21.1μgm⁻²s⁻¹ in December and January, respectively. Stepwise multiple regression analysis between storage energy [Δ H_s( P)] and fluxes of CO₂, CH₄, H (sensible heat), H_L (latent heat of evaporation), Δ R (budget closer energy) showed that the combined explained variability for CO₂ flux, evapotranspiration and budget closer energy (39%) was less than that of CH₄ and sensible heat flux (46%). The extent of warming effect by CH₄ and sensible heat flux was predominant over the resultant cooling effect due to the processes such as photosynthesis, evapotranspiration and albedo. The mangrove forest with two trademarks of low albedo and high surface roughness was poorly coupled to the environment.

Keywords: Energy dynamics; Biosphere–atmosphere interaction; Carbon dioxide; Methane; Water vapour; Mangrove forest; Sundarban; India

Sensitivity of biogenic emissions simulated by a land-surface model to land-cover representations by Lindsey E. Gulden; Zong-Liang Yang; Guo-Yue Niu (pp. 4185-4197).

We evaluate the sensitivity of biogenic emissions simulated by a land-surface model (LSM) to different representations of land-cover vegetation. We drive the community land model on a 0.1° grid over Texas, USA, from 1993 to 1998 using bilinearly interpolated North American Regional Reanalysis data. Two land-cover datasets provide the starting point for analysis: (1) a satellite-derived vegetation and soil-color database and (2) a vegetation-distribution dataset derived from ground surveys. These datasets help us to qualitatively characterize the uncertainty in land-cover representations. We systematically vary the datasets to examine the sensitivity of modeled emissions to variation in representation of bare-soil fraction, vegetation-type distribution, and phenology.Different datasets’ representation of vegetation-type distribution leads to simulated mean statewide total biogenic emissions that vary by a factor of 3. Variation in specified bare-soil fraction causes simulated statewide average emissions that vary by a factor of 1.7. Scaling leaf area index values within reasonable bounds causes a near-linear change in simulated emissions. Differences in simulated values are the largest for major metropolitan regions and for eastern and central Texas, where biogenic emissions are the highest and where tropospheric ozone pollution is a significant concern. Changing bare-soil fraction alters simulated vegetation temperature and consequently indirectly affects modeled emissions (⩽16% of inherent emissions capacity). Our estimates of the model sensitivity to land-cover representation are consistent with those for other regions.

Keywords: Biogenic emissions; Sensitivity analysis; Land-surface model; Air quality; Land-cover dataset; Vegetation; BVOCs; Isoprene; Monoterpene

Reductions in ozone concentrations due to controls on variability in industrial flare emissions in Houston, Texas by Junsang Nam; Mort Webster; Yosuke Kimura; Harvey Jeffries; William Vizuete; David T. Allen (pp. 4198-4211).

High concentrations of ozone in the Houston/Galveston area are associated with industrial plumes of highly reactive hydrocarbons mixed with NO _x. The emissions leading to these plumes can have significant temporal variability, and photochemical modeling indicates that the emissions variability can lead to increases and decreases of 10–50ppb, or more, in ozone concentrations. Therefore, in regions with extensive industrial emissions, accounting for emission variability can be important in accurately predicting peak ozone concentrations, and in assessing the effectiveness of emission-control strategies. This work compares the changes in ozone concentrations associated with two strategies for reducing flare emissions in Houston, Texas. One strategy eliminates the highest emission flow rates, that occur relatively infrequently, and a second strategy reduces emissions that occur at a nearly constant level. When emission variability is accounted for in air quality modeling, these control scenarios are both predicted to be much more effective in reducing the expected value of daily maximum ozone concentrations than if similar reductions in the mass of emissions are made and constant emissions are assumed. The change in the expected value of daily maximum ozone concentration per ton of emissions reduced, when emissions variability is accounted for, is 5–10 times the change predicted when constant (deterministic) inventories are used. Strategies that eliminate the infrequent largest emissions are more effective at reducing the highest localized ozone concentrations than changes in nearly constant emissions.

Keywords: Photochemical grid model; Highly reactive volatile organic compounds (HRVOC); Ozone; Uncertainty analysis

On the anomalous behavior of the Lagrangian structure function similarity constant inside dense canopies by Davide Poggi; Gabirel G. Katul; Massimo Cassiani (pp. 4212-4231).

The choice of the Kolmogorov constant ( C₀) in Lagrangian Stochastic Models (LSMs) for canopy flows remains a subject of debate and uncertainty. This uncertainty stems from the fact that canopy flows are highly dissipative, lack a well-defined inertial subrange (ISR) in their energy cascade, and in the deeper layers of the canopy, the attenuation of turbulence can amplify finite Reynolds number effects on C₀. From the analysis here, it was shown that C₀ inside dense canopies is reduced relative to its value in the atmospheric surface layer (ASL) primarily due to wake production (a factor of 5), followed by finite Reynolds number effects (a factor of 1.5 at most). The short-circuiting of the energy cascade tends to increase C₀ though not enough to compensate for the other two reductions. These results are qualitatively consistent with theoretical predictions of a reduced C₀ with an increased anisotropy and localized acceleration when referenced to a homogeneous isotropic stationary turbulence. Simplified scaling arguments were proposed for each of these three effects and tested using flume experiments. The fact that C₀ may vary nonlinearly inside canopies complicates inverse estimates of C₀ that use fitting Lagrangian dispersion models (LDMs) to mean concentration measurements. The C₀ values inferred from such an approach were shown to be sensitive to the source location (especially inside the canopy) and concentration sampling points. On a positive note, the fact that C₀ may vary within the canopy does not require any revisions to the well-mixed condition because LDM are not sensitive to gradients in C₀. A phenomenological model that accounts for the vertical variation in C₀ as a function of the most elementary flow variables, the mean velocity and canopy adjustment length scale, is proposed but its general applicability remains to be tested.

Keywords: Canopy turbulence; Energy short-circuiting; Eulerian and Lagrangian time scales; Kolmogorov constant; Lagrangian dispersion models; Wake production

The impact of topography and urban building parameterization on the photochemical ozone concentration of Seoul, Korea by Hwa Woon Lee; H.-J. Hyun-Jung Choi; Soon-Hwan Lee; Yoo-Keun Kim; Woo-Sik Jung (pp. 4232-4246).

Several numerical experiments have been undertaken in order to clarify the impacts of detailed topography and building parameterization on meteorological and photochemical environments. In this study, we carried out a comparative examination on the meteorological fields of topographies that had different resolutions and building information. By analyzing practical urban ground conditions, we revealed that there were large differences in the ozone concentration for each run. The MM5-CMAQ model was used to assess the ozone differences in each case, during the episode day in Seoul, Korea.Meteorological conditions estimated by MM5 command a great influence on the dispersion of air pollutants in complex areas. The reasonable feature of topography that has a high resolution induces a steeper slope in comparison with that of a topography that has a low resolution. Therefore, there is a difference in orographic forcing between the two sets of simulations. This causes a difference in the estimated ozone concentration. A higher ozone concentration tends to be forecasted when using topography data that have a high resolution with an appropriate limitation to the mixing height and the nocturnal boundary layer. The urban buildings parameterization scheme is also strongly associated with the estimation of meteorological and photochemical fields. The length of homogeneous roughness in an urban area corresponds to observations in all other parameterizations of urban buildings in this study.

Keywords: Topography; Urban building; Photochemical modeling; Ozone concentration; Numerical simulation

Origin of observed high⁷Be and mineral dust concentrations in ambient air on the Island of Tenerife by F. Hernandez; Rodriguez S. Rodríguez; L. Karlsson; Alonso-Perez S. Alonso-Pérez; Lopez-Perez M. López-Pérez; J. Hernandez-Armas; E. Cuevas (pp. 4247-4256).

Temporal series of atmospheric PM₁ and PM₁₀ matter (particulate matter with aerodynamic diameter below 1 and 10μm) as well as⁴⁰K and⁷Be concentrations in aerosol filters, collected in the Island of Tenerife from 30 June 2003 until 17 January 2005, were analysed here to: (1) study the variability of⁷Be in the atmosphere at this site and (2) to identify the origin of high⁷Be events and check their possible connection with the transport of Saharan dust to Tenerife.A complex relationship was observed between PM₁₀ matter and⁷Be concentrations in the measured aerosol filters. Due to this fact, the analysed atmospheric events had to be grouped in: (I) high⁷Be and high PM₁₀ matter events; (II) low⁷Be and high PM₁₀ matter events; and (III) high⁷Be and low PM₁₀ matter events. The low⁷Be and low PM₁₀ matter events were not considered in this study. The results indicated that four times during the study period significant concentrations of⁷Be were observed with the arrival of suspended material from the African continent. An enhanced scavenging effect of the⁷Be available in the aerosol transport zone by the re-suspended material is believed to have caused these detected increments in local atmospheric concentrations. Seventy-two hours forecasts created with the Dust Regional Atmospheric model (DREAM model) for these events, also, seem to support this hypothesis.

Keywords: Berylium-7; Atmospheric aerosols; Gamma spectrometry; Saharan dust; Particulate matter (PM; ₁₀; and PM; ₁; )

In situ measurements of particle number concentration, chemically resolved size distributions and black carbon content of traffic-related emissions on German motorways, rural roads and in city traffic by J. Schneider; U. Kirchner; S. Borrmann; R. Vogt; V. Scheer (pp. 4257-4268).

In-situ measurements of various properties of traffic-related aerosol particles have been performed with a mobile laboratory. The measured aerosol quantities include particle chemical composition (sulfate, nitrate, total organic matter, ammonium, black carbon) as well as particle size distributions covering diameters from 10 to 300nm, and total particle number density. Additionally, gas phase emissions (CO₂, NO, NO₂) were monitored. We performed six measurement drives in the vicinity of the city of Aachen (population ca. 260,000) at 50.8°N, 6.1°E in Germany on motorways, rural roads, and in the inner city of Aachen in June 2005.The results indicate that the main influence of traffic on the aerosol properties results in soot particles coated with organic matter, having a modal diameter around 100nm (“soot mode”). The abundance of these particles was found to be highest in the inner city traffic. Nucleation mode particles (around 30nm) have been observed occasionally during truck chasings on motorways. These particles consisted mainly of organic compounds but included possibly also a sulfuric acid core. Data observed under “motorway background” conditions were similar to the rural regional road data. Highest number concentrations have been observed during truck chasings. Comparison between non-refractory (here with respect to 600°C) and total particle volume indicated a higher contribution of refractory material under all traffic-influenced conditions compared to rural road data. Fuel specific emission ratios were derived for a subset of 18 truck-chasing experiments, yielding (8.3±5.8)×10¹⁵kg⁻¹ for particle number, 224±136mgkg⁻¹ for black carbon, 125±125mgkg⁻¹ for organic matter, 17±12gkg⁻¹ for NO and 18±14gkg⁻¹ for NO _x (mean values and standard deviations).

Keywords: Diesel particles; Traffic emissions; Urban pollution; Aerosol mass spectrometry

Dispersion and photochemical oxidation of reduced sulfur compounds in and around a large industrial complex in Korea by Sang-Keun Song; Zang-Ho Shon; Ki-Hyun Kim; Yoo-Keun Kim; Raktim Pal (pp. 4269-4279).

In this study, the environmental behavior of reduced sulfur compounds (RSCs: H₂S, DMS, CS₂, DMDS, and CH₃SH) was investigated in an area influenced by strong anthropogenic processes based on a numerical modeling approach. The RSC emission concentrations were measured from multiple locations around the Ban-Wall industrial complex (BWIC) in the city of An San (AS), Korea, during a series of field campaigns held between August 2004 and September 2005. These emissions were then used as input for a CALPUFF dispersion model with the 34 dominant chemical reactions for RSCs. The impact of RSC emission on SO₂ concentrations was assessed further in the study areas. The model study indicated the possibility that RSCs emitted in and around the BWIC can exert a direct impact on the ambient SO₂ concentration levels in its surrounding areas with the most prominent effect observed during summer. Our prediction indicated that a significant fraction of SO₂ was produced photochemically in and around the BWIC during the summer (about 30% of total SO₂ concentrations) and fall events (∼20%). These photochemical productions of SO₂ were mainly ascribable to H₂S (∼60% of total contributions) and DMDS (∼25%) out of all five target RSCs. Meteorological contribution (dispersion) to SO₂ concentration level was also highest during summer.

Keywords: Dispersion; Reduced sulfur; Industrial complex; SO; ₂; CALPUFF

Data mining to characterize ozone behavior in Baltimore and Washington, DC by Kenneth J. Walsh; Matthew Milligan; Michael Woodman; John Sherwell (pp. 4280-4292).

Data mining exercises were used to describe long-term ambient ozone concentrations in Baltimore and Washington based on meteorological conditions as well as upwind and previous day concentrations. Ozone production occurs mainly during the summer months and is influenced by a variety of meteorological parameters. Fifteen years of daily ozone measurements (May–September) were subset into five daily meteorological clusters using an expectation–maximization technique (based on available temperature, solar radiation, precipitation, and other meteorological parameters). Rule association and classifier models were used to quantify the contributions from high overnight ozone concentrations at upwind rural sites (21–36ppb). Data clustering followed by further subsetting was used to examine the effects of low level jets (on average 5–7ppb higher when jets were observed).To interpret interannual ozone trends, the year-to-year fluctuations in summertime meteorology must be accounted for and adjusted. The historical trends of each meteorological cluster were measured to determine which trends were statistically significant. By separately analyzing the trends of each meteorological cluster, the results were weather-normalized to discount the effects of rainy or drought years in the analyses.Seven different ozone parameters were investigated, and three of the five clusters showed weak or no trends for the time periods 1991–2004 and 1999–2004. However, a Baltimore Cluster which represents sunny conditions with variable winds and a high temperature difference between morning surface and aloft temperatures showed statistically significant decreases in three ozone parameters from 1991 through 2004. The most compelling evidence came from the cluster representing sunny and hot conditions with high wind speeds from the west and northwest and showing statistically significant decreasing trends for six of the seven ozone parameters from 1999 through 2004.

Keywords: Ozone; Data mining; Interannual trends; Clustering; Low level jet

Aspects of year-long differential optical absorption spectroscopy and ground station measurements in an urban street canyon near industrial pollution sources by S. Zoras; A.G. Triantafyllou; V. Evagelopoulos (pp. 4293-4303).

The annual performance of a differential optical absorption spectroscopy (DOAS) system in combination with a ground monitoring station was assessed in an urban street canyon of a medium-sized city, Greece. The urban environment is surrounded by complex terrain and located in proximity to coal-fired power plants. One-year hourly concentrations of ozone, nitrogen dioxide (NO₂), and sulphur dioxide (SO₂) that have been measured by DOAS were correlated against data from a conventional ground station. Concentrations of volatile organic compounds (benzene, toluene, and p, m-xylene) have also been presented and their photochemical role was related to their degree of reactivity. Experimental data of photochemical pollutants were significantly correlated against meteorology during a 7-day period. The parallel monitoring at ground and DOAS path levels has contributed in the verification of distant pollutants’ transfer from the industry. The importance of wind speed in the photochemical production of ozone by was also stipulated the distinction of urban and rural conditions.

Keywords: DOAS; Urban street canyon; Air pollutants; Toluene/benzene ratio; Power plants

Pseudo-simultaneous measurements for the vertical variation of coarse, fine and ultrafine particles in an urban street canyon by Prashant Kumar; Paul Fennell; David Langley; Rex Britter (pp. 4304-4319).

The vertical variation of particle number distributions (PNDs) and concentrations in a street canyon is the result of the competing influences of meteorology, traffic and transformation processes overall and for various particle size ranges. A recently developed instrument, the ‘fast-response differential mobility spectrometer DMS500’, measured PNDs in the 5–2738nm range, pseudo-simultaneously, at four different heights ( z/ H=0.09, 0.19, 0.40 and 0.64) on the leeward side of an 11.6-m-deep street canyon which had a height-to-width ratio of near unity. Measurements were made in Cambridge, UK, between 20 and 21 March 2007.The PNDs were bimodal with the same shape at each height, and with similar values of both the peak and geometric mean particle diameters in each mode. This suggested that transformation processes were not important. Coagulation and condensation time scales were comparable and large, and these processes should have had a negligible effect on the PNDs.The particle number concentrations (PNCs) changed significantly with height from a maximum at z/ H=0.19 and decreasing towards both the lowest ( z/ H=0.09) and highest ( z/ H=0.64) sampling points. The decrease in PNCs with height in the upper part of the canyon was attributed to the removal of particles as a result of mass exchange between street canyon and the wind above while the reduction in the PNC towards street level was thought to be due to dilution and dry deposition.Over 99% of the PNCs were found in 10–300nm range whereas the particle mass concentrations were almost equally distributed between the 10–1000nm and 1000–2738nm size range at each height. The PNCs in the 10–30nm and the 30–300nm size range were linearly correlated with the traffic volume but poorly correlated with the rooftop wind speed.

Keywords: Street canyon; Particle number distributions and concentrations; Vertical concentration profiles; Ultrafine particles

Long-term spatial distributions and trends of ambient CO concentrations in the central Taiwan Basin by Yu Chi Lin; Yung Yao Lan; Ben-Jei Tsuang; Guenter Engling (pp. 4320-4331).

Long-term spatial distributions and trends of atmospheric carbon monoxide (CO) concentrations in the central Taiwan Basin were investigated by analysis of CO data obtained from the Taiwan Air Quality Monitoring Network (TAQMN). The influence of meteorological conditions on the CO patterns was also analyzed in this paper. The results showed the highest CO concentrations were found in the vicinity of urban areas with a 13-yr mean value of 0.79±0.16ppm. This was associated with the most intensive anthropogenic CO emissions at the urban sites. For all sites, lower CO levels were consistently observed during the summer season. This was explained by favorable conditions for dispersion and loss of CO via photochemical reactions. Analysis of wind fields and backward trajectories revealed that two types of synoptic sea breezes directly influenced the CO spatial distributions in the basin. During autumn to spring, northerly flow accompanied by pollutants traveled to inland areas, resulting in higher CO concentrations in the remote areas. During summer, breezes coming from the sea or areas to the south with lower CO emissions, resulted in more uniform spatial distributions of CO in the study region. While CO concentrations exhibited decreasing trends, the average CO mixing ratio from 1994 through 2006 decreased at a rate of approximately 0.02ppmyr⁻¹ in the central Taiwan Basin.

Keywords: Carbon monoxide; Long-term trends; CO emissions; Backward trajectory; Sea breeze

Particle- and gas-phase emissions of polycyclic aromatic hydrocarbons from two-stroke, 50-cm³ mopeds by Pasquale Spezzano; Paolo Picini; Dario Cataldi; Fabrizio Messale; Claudio Manni (pp. 4332-4344).

The emissions of gas- and particle-phase polycyclic aromatic hydrocarbons (PAHs) were evaluated in the exhaust of 10 mopeds (4 EURO-0, 4 EURO-1 and 2 EURO-2) equipped with two-stroke engines with displacement of 50cm³. Sampling was performed on a dynamometer bench both during the “cold-start” and the “hot” phases of the ECE-47 driving cycle.Eighteen PAHs were quantified and total PAH emission factors (∑PAH) ranged from 1790 to 15,059μgkm⁻¹. Expressed in benzo( a)pyrene equivalent (BaP_eq), emission factors ranged 4.7–86.3μgkm⁻¹. PAH emissions are reduced according to the legislation class: EURO-0>EURO-1>EURO-2. PAH emission factors were greater during the cold-start phase than the hot phase of the ECE-47 cycle. Results show that despite their small engine size, two-stroke mopeds can emit amounts of particulate PAHs comparable or even higher than PAH emissions reported elsewhere from gasoline- and diesel-powered passenger cars and light- and heavy-duty vehicles.

Keywords: Exhaust emission; Moped; PAH; Particulate matter; Two-wheeler

Adaptation of an ammonia volatilization model for a naturally ventilated dairy building by Frederick Kwame Teye; Mikko Hautala (pp. 4345-4354).

A theoretical ammonia emission model was adapted to the conditions prevailing in a naturally ventilated dairy building. The relevant parameters including the mass transfer coefficient needed for the model were experimentally measured. Ammonia emissions from the dairy building were also calculated from directly measured ammonia concentrations and carbon dioxide mass balances from the dairy building. The results of the theoretical model for ammonia emission from manure were compared with the experimentally measured emissions inside the dairy building.The absolute mean difference and standard error between ammonia emissions from the theoretical model and the experimental measurements was 0.013±0.005gm⁻³h⁻¹. Parametric inaccuracy range in both emission estimation methods was 40%. A factor of ten difference was recorded between day and night ammonia emission rates. Ammonia emissions varied between 0.04 and 0.58gm⁻²h⁻¹. The critical parameters that need to be considered in reducing ammonia emissions in dairy buildings according to the theoretical emission model were manure temperature, pH and total ammoniacal nitrogen of the manure.

Keywords: Emission; Dairy; Manure; Ammonia; Modelling

Prevalence of culturable airborne spores of selected allergenic and pathogenic fungi in outdoor air by C.M. Céline M. O’Gorman; Hubert T. Fuller (pp. 4355-4368).

Temporal and spatial variations in airborne spore concentrations of selected allergenic and pathogenic fungi were examined in Dublin, Ireland, in 2005. Air samples were taken at four outdoor locations in the city every 2 weeks, coupled with measurements of meteorological conditions. Total culturable airborne fungal spore concentrations in Dublin ranged from 30–6800 colony forming units per cubic metre of air (CFUm⁻³) over the 12-month period. Cladosporium, Penicillium, Aspergillus and Alternaria spores were constantly present in the Dublin atmosphere, representing >20% of the total culturable spore count. Concentrations of Cladosporium increased significantly in summer and reached allergenic threshold levels, peaking at over 3200CFUm⁻³ in August. Penicillium spore concentrations never reached allergenic threshold levels, with average concentrations of <150CFUm⁻³. Alternaria conidia formed only 0.3% of the total culturable fungal spore count and concentrations never exceeded 50CFUm⁻³, attributable to the coastal position of Dublin and its low levels of arable production. The opportunistic human pathogen Aspergillus fumigatus was present throughout the year in nominal concentrations (<10CFUm⁻³), but sporadic high counts were also recorded (300–400CFUm⁻³), the potential health implications of which give cause for concern. Spores of neither Cryptococcus neoformans nor Stachybotrys chartarum were detected, but airborne basidiospores of Schizophyllum commune were evidenced by the dikaryotization of monokaryon tester strains following exposure to the air. The relationships between airborne fungal spore concentrations and meteorological factors were analysed by redundancy analysis and revealed positive correlations between temperature and Cladosporium and relative humidity and Penicillium and Aspergillus.

Keywords: Allergenic fungi; Dublin; Fungal spores; Human pathogens; Seasonal variation; Urban air

Generation of hydroxyl radicals from dissolved transition metals in surrogate lung fluid solutions by Edgar Vidrio; Heejung Jung; Cort Anastasio (pp. 4369-4379).

^{Epidemiological research has linked exposure to atmospheric particulate matter (PM) to several adverse health effects, including cardiovascular and pulmonary morbidity and mortality. Despite these links, the mechanisms by which PM causes adverse health effects are poorly understood. The generation of hydroxyl radical (}^{OH) and other reactive oxygen species (ROS) through transition-metal-mediated pathways is one of the main hypotheses for PM toxicity. In order to better understand the ability of particulate transition metals to produce ROS, we have quantified the amounts of}^{OH produced from dissolved iron and copper in a cell-free, surrogate lung fluid (SLF). We also examined how two important biological molecules, citrate and ascorbate, affect the generation of}^{OH by these metals. We have found that Fe(II) and Fe(III) produce little}^{OH in the absence of ascorbate and citrate, but that they efficiently make}^{OH in the presence of ascorbate and this is further enhanced when citrate is also added. In the presence of ascorbate, with or without citrate, the oxidation state of iron makes little difference on the amount of}OH formed after 24^{h. In the case of Cu(II), the production of}^{OH is greatly enhanced in the presence of ascorbate, but is inhibited by the addition of citrate. The mechanism for this effect is unclear, but appears to involve formation of a citrate–copper complex that is apparently less reactive than free, aquated copper in either the generation of hydrogen peroxide (HOOH) or in the Fenton-like reaction of copper with HOOH to make}^{OH. By quantifying the amount of}^{OH that Fe and Cu can produce in surrogate lung fluid, we have provided a first step into being able to predict the amounts of}OH that can be produced in the human lung from exposure to PM containing known amounts of transition metals.

Keywords: Reactive oxygen species (ROS); Hydroxyl radical; Transition metals; Particulate matter; Fenton reaction

Characterization of chemical and particulate emissions from aircraft engines by Harshit Agrawal; Aniket A. Sawant; Karel Jansen; J. Wayne Miller; David R. Cocker III (pp. 4380-4392).

This paper presents a series of measurements from four on-wing, commercial aircraft engines, including two newer CFM56-7 engines and two earlier CFM56-3 engines. Samples were collected from each engine using a probe positioned behind the exhaust nozzle of the aircraft, chocked on a concrete testing pad. The emission factors for particulate matter mass, elemental and organic carbon, carbonyls, polycyclic aromatic hydrocarbons, n-alkanes, dioxins, metals and ions are reported for four different engine power setting modes. The emissions indices of particulate matter, elemental and organic carbon are highly power dependent for these engines. Particulate matter emission indices (gkg⁻¹ fuel) are found to increase from 1.1E−02 to 2.05E−01 with increase in power from idle to 85%. The elemental carbon to organic carbon varies from 0.5 to 3.8 with change in power from idle to 85%. The carbonyl emissions are dominated by formaldehyde. The emission index of formaldehyde ranges from 2.3E−01 to 4.8E−01gkg⁻¹ fuel. The distribution of metals depends on the difference in the various engines. The dioxin emissions from the aircraft engines are observed to be below detection limit.

Keywords: Jet turbine emissions; PAHs; Carbonyls; Particulate matter; Aircraft

Ambient mixing ratios of nonmethane hydrocarbons (NMHCs) in two major urban centers of the Pearl River Delta (PRD) region: Guangzhou and Dongguan by Barbara Barletta; Simone Meinardi; Isobel J. Simpson; Shichun Zou; F. Sherwood Rowland; Donald R. Blake (pp. 4393-4408).

The Pearl River Delta (PRD) region can be considered one of the most economically developed areas of mainland China. In September 2005, a total of 96 whole air samples were collected in Guangzhou and Dongguan, two important urban centers of the PRD region. Guangzhou is considered the economic center of Guangdong province, and Dongguan is a rapidly expanding industrial city. Here, we report mixing ratios of 50 nonmethane hydrocarbons (NMHCs) that were quantified in the ambient air of these PRD centers. The discussion focuses on understanding the main sources responsible for NMHC emissions, and evaluating the role of the identified sources towards ozone formation. Propane was the most abundant species in Guangzhou, with an average mixing ratio of 6.8ppbv (±0.7ppbv S.E.), compared to 2.5±0.2ppbv in Dongguan. Toluene was the most abundant hydrocarbon in Dongguan (6.1±0.8ppbv, compared to 5.9±0.7ppbv in Guangzhou). Based on an analysis of the correlation between vehicular-emitted compounds and the measured NMHCs, together with the benzene-to-toluene (B/T) ratio, vehicular emission appears to be the dominant source of NMHCs measured in Guangzhou. By contrast, selected species (including toluene) in many of the Dongguan samples were influenced by an additional source, most likely related to industrial activities. A specific B/T ratio (<0.20) is proposed here and used as indicator of samples strongly affected by industrial emissions. The ozone formation potential (OFP) is calculated, and the role of the different NMHCs associated with industrial and combustion sources is evaluated.

Keywords: Urban air quality; Nonmethane hydrocarbons; China; Gaschromatography; Ozone formation potential

A new scheme to predict chaotic time series of air pollutant concentrations using artificial neural network and nearest neighbor searching by Ajit Kumar Gautam; A.B. Chelani; V.K. Jain; S. Devotta (pp. 4409-4417).

Air pollution time series is often characterized as chaotic in nature. The prediction using conventional statistical techniques and neural network with backpropagation algorithm, which is most widely applied, do not give reliable prediction results. The new algorithm is therefore proposed to predict the chaotic time series based on the artificial neural network technique. The training to the network is similar to the conventional technique of learning, whereas for testing and prediction purpose, the algorithm searches for the nearest neighbor of the presented test and/or prediction patterns in the training set. The case study of well-known chaotic time series, namely, Lorenz map and real data of ozone concentration are provided to examine the performance of proposed scheme. The most widely used backpropagation algorithm is also used for comparison purpose. The out performance of proposed scheme over backpropagation algorithm is observed. The proposed scheme provides the network, the ability to capture the underlying dynamics of the chaotic time series, as the input patterns are presented one by one to the network.

Keywords: Chaotic time series; Neural networks; Nearest neighbor search; Air pollutant concentration

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Atmospheric Environment (v.42, #18)

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Atmospheric Environment (v.42, #18)