Personal exposures to NO2 in the EXPOLIS-study: relation to residential indoor,outdoor and workplace concentrations in Basel,Helsinki and Prague

Personal exposures, residential indoor, outdoor and workplace levels of nitrogen dioxide (NO₂) were measured for 262 urban adult (25–55 years) participants in three EXPOLIS centres (Basel; Switzerland, Helsinki; Finland, and Prague; Czech Republic) using passive samplers for 48-h sampling periods during 1996–1997. The average residential outdoor and indoor NO₂ levels were lowest in Helsinki (24±12 and 18±11 μg m⁻³, respectively), highest in Prague (61±20 and 43±23 μg m⁻³), with Basel in between (36±13 and 27±13 μg m⁻³). Average workplace NO₂ levels, however, were highest in Basel (36±24 μg m⁻³), lowest in Helsinki (27±15 μg m⁻³), with Prague in between (30±18 μg m⁻³). A time-weighted microenvironmental exposure model explained 74% of the personal NO₂ exposure variation in all centres and in average 88% of the exposures. Log-linear regression models, using residential outdoor measurements (fixed site monitoring) combined with residential and work characteristics (i.e. work location, using gas appliances and keeping windows open), explained 48% (37%) of the personal NO₂ exposure variation. Regression models based on ambient fixed site concentrations alone explained only 11–19% of personal NO₂ exposure variation. Thus, ambient fixed site monitoring alone was a poor predictor for personal NO₂ exposure variation, but adding personal questionnaire information can significantly improve the predicting power.     

Application of a Lagrangian particle model to assess the impact of harbour,industrial and urban activities on air quality in the Taranto area,Italy

This paper evaluates the relative impact on air quality of harbour emissions, with respect to other emission sources located in the same area. The impact assessment study was conducted in the city of Taranto, Italy. This area was considered as representative of a typical Mediterranean harbour region, where shipping, industries and urban activities co-exist at a short distance, producing an ideal case to study the interaction among these different sources. Chemical and meteorological field campaigns were carried out to provide data to this study. An emission inventory has been developed taking into account industrial sources, traffic, domestic heating, fugitive and harbour emissions. A 3D Lagrangian particle dispersion model (SPRAY) has then been applied to the study area using reconstructed meteorological fields calculated by the diagnostic meteorological model MINERVE. 3D short term hourly concentrations have been computed for both all and specific sources. Industrial activities are found to be the main contributor to SO₂. Industry and traffic emissions are mainly responsible for NO_x simulated concentrations. CO concentrations are found to be mainly related to traffic emissions, while primary PM₁₀ simulated concentrations tend to be linked to industrial and fugitive emissions. Contributions of harbour activities to the seasonal average concentrations of SO₂ and NO_x are predicted to be up to 5 and 30 μg m⁻³, respectively to be compared to a overall peak values of 60 μg m⁻³ for SO₂ and 70 μg m⁻³ for NO_x. At selected urban monitoring stations, SO₂ and NO_x average source contributions are predicted to be both of about 9% from harbour activities, while 87% and 41% respectively of total concentrations are predicted to be of industrial origin.     

A semi-empirical model for urban PM10 concentrations,and its evaluation against data from an urban measurement network

We have developed a model for evaluating the mass-based concentrations of urban particulate matter. The basic model assumption is that local vehicular traffic is responsible for a substantial fraction of the street-level concentrations of both PM₁₀ and NO_x, either due to primary emissions or resuspension from street surfaces. The modelling system utilises the data from an air quality monitoring network in the Helsinki Metropolitan Area. We have determined linear relationships between the measured urban PM₁₀ data against those of NO_x in various urban surroundings, based on continuously measured hourly concentration values. The data was obtained from two stations in central Helsinki and one suburban station in the Helsinki Metropolitan Area during a period of 3 yr, from 1996 to 1998. The model also includes a treatment of the regional background concentrations, and resuspended particulate matter. The model performance was evaluated against the measured PM₁₀ data from the above-mentioned three stations and from two other stations, using data that was measured in 1999. We used two alternative model versions, one based on separate correlation parameters (PM₁₀ vs. NO_x) for each station, and another based on parameters averaged over the stations considered. We analysed the agreement between the measured and predicted hourly concentration time series, utilising the values of the fractional bias (FB) and the so-called index of agreement (IA). As expected, the model predicts relatively well the yearly mean concentrations of PM₁₀: the FB values range from −0.05 to +0.09. Model performance is also relatively good when predicting the yearly mean values that are classified separately for each hour of the day: the corresponding IA values range from 0.85 to 0.96. However, model performance is substantially worse in predicting the hourly time series of the year: the IA values using the station-specific parameters range from 0.46 to 0.65. The model was applied in evaluating the yearly average spatial concentration distribution of PM₁₀ in central Helsinki, based on the corresponding modelled NO_x concentrations. With re-evaluation of a few parameters that can be determined empirically, the model could be evaluated, and most probably applied, in other urban areas as well.     

Application of CALINE4 to roadside NO/NO2 transformations

The CALINE4 roadway dispersion model has been applied to concentrations of NO_x and NO₂ measured near Gandy Boulevard in Tampa, FL (USA) during May 2002. A NO_x emission factor of 0.86 gr mi⁻¹ was estimated by treating NO+NO₂ (NO_x) as a conserved species and minimizing the differences between measured and calculated NO_x concentrations. This emission factor was then used to calculate NO₂ concentrations using the NO/NO₂ transformation reactions built into CALINE4. A comparison of measured and calculated NO₂ concentrations indicates that for ambient O₃ concentrations less than 40 ppb the model under-predicts the chemical transformation of NO. The enhanced transformation of NO may be due to reactions of NO with oxidants such as peroxy radicals that are present either in the atmosphere or in vehicle exhaust.     

Air pollution characteristics associated with mesoscale atmospheric patterns in northwest continental Europe

An impact related daily air quality index (DAQx), calculated for 15 air quality monitoring stations (traffic, background, and industry) in Belgium, France, Germany and Luxembourg, was compared to mesoscale atmospheric patterns between 2001 and 2007. Meteorological conditions were described by the Hess and Brezowsky synoptic weather classification system and gridded data of the EU FP6 ENSEMBLES project of total precipitation and mean surface temperature. DAQx values indicate sufficient to poor air quality in the urban area of Brussels and at urban traffic stations, as well as satisfactory air quality at the background stations. The air quality index refers to more than 90% to the presence of high PM₁₀, O₃ and NO₂ concentrations. SO₂ and CO play only a minor role. The investigation of weather regimes indicates that zonal and mixed cyclonic circulation regimes are associated with better air quality than meridional and anticyclonic weather regimes. In general, weather regimes with high daily precipitation lead to better air quality than dryer air masses because of lower contribution of PM₁₀ to the air quality index. A trend analysis of weather regimes from 1978 to 2007 shows significant (α = 0.05) positive trends for weather classes associated with lower PM₁₀ concentrations. The results of a case study at a German station examining the relationship between PM₁₀ concentrations and local meteorological quantities (wind speed and precipitation) confirm the results of the regional analysis.     

Predictive NOx emission monitoring on board a passenger ferry

NO_x emissions from a medium speed diesel engine on board a servicing passenger ferry have been indirectly measured using a predictive emission monitoring system (PEMS) over a 1-yr period. Conventional NO_x measurements were carried out with a continuous emission monitoring system (CEMS) at the start of the study to provide historical data for the empirical PEMS function. On three other occasions during the year the CEMS was also used to verify the PEMS and follow any changes in emission signature of the engine. The PEMS consisted of monitoring exhaust O₂ concentrations (in situ electrochemical probe), engine load, combustion air temperature and humidity, and barometric pressure. Practical experiences with the PEMS equipment were positive and measurement data were transferred to a land-based office by using a modem data communication system. The initial PEMS function (PEMS1) gave systematic differences of 1.1–6.9% of the calibration domain (0–1725 ppm) and a relative accuracy of 6.7% when compared with CEMS for whole journeys and varying load situations. Further improvements on the performance could be obtained by updating this function. The calculated yearly emission for a total engine running time of 4618 h was 316 t NO_x±38 t and the average NO_x emission corrected for ambient conditions 14.3 g kWh_corr⁻¹. The exhaust profile of the engine in terms of NO_x, CO and CO₂ emissions as determined by CEMS was similar for most of the year. Towards the end of the study period, a significantly lower NO_x emission was detected which was probably caused by replacement of fuel injector nozzles. The study suggests that PEMS can be a viable option for continuous, long-term NO_x measurements on board ships.     

Ozone response to precursor controls: comparison of data analysis methods with the predictions of photochemical air quality simulation models

Comparisons were made between the predictions of six photochemical air quality simulation models (PAQSMs) and three indicators of ozone response to emission reductions: the ratios of O₃/NO_z and O₃/NO_y and the extent of reaction. The values of the two indicator ratios and the extent of reaction were computed from the model-predicted mixing ratios of ozone and oxidized nitrogen species and were compared to the changes in peak 1 and 8 h ozone mixing ratios predicted by the PAQSMs. The ozone changes were determined from the ozone levels predicted for base-case emission levels and for reduced emissions of volatile organic compounds (VOCs) and oxides of nitrogen (NO_x). For all simulations, the model-predicted responses of peak 1 and 8 h ozone mixing ratios to VOC or NO_x emission reductions were correlated with the base-case extent of reaction and ratios of O₃/NO_z and O₃/NO_y. Peak ozone values increased following NO_x control in 95% (median over all simulations) of the high-ozone (>80 ppbv hourly mixing ratio in the base-case) grid cells having mean afternoon O₃/NO_z ratios less than 5 : 1, O₃/NO_y less than 4 : 1, or extent less than 0.6. Peak ozone levels decreased in response to NO_x reductions in 95% (median over all simulations) of the grid cells having peak hourly ozone mixing ratios greater than 80 ppbv and where mean afternoon O₃/NO_z exceeded 10 : 1, O₃/NO_y was greater than 8 : 1, or extent exceeded 0.8. Ozone responses varied in grid cells where O₃/NO_z was between 5 : 1 and 10 : 1, O₃/NO_y was between 4 : 1 and 8 : 1, or extent was between 0.6 and 0.8. The responses in such grid cells were affected by ozone responses in upwind grid cells and by the changes in ozone levels along the upwind boundaries of the modeling domains.     

Aircraft measurements of O3, NOx,CO, VOCs,and SO2 in the Yangtze River Delta region

In this study, air pollutants, including ozone (O₃), nitrogen oxides (NO_x = NO + NO₂), carbon monoxides (CO), sulfur dioxide (SO₂), and volatile organic compounds (VOCs) measured in the Yangtze River Delta (YRD) region during several air flights between September/30 and October/11 are analyzed. This measurement provides horizontal and vertical distributions of air pollutants in the YRD region. The analysis of the result shows that the measured O₃ concentrations range from 20 to 60 ppbv. These values are generally below the US national standard (84 ppbv), suggesting that at the present, the O₃ pollutions are modest in this region. The NO_x concentrations have strong spatial and temporal variations, ranging from 3 to 40 ppbv. The SO₂ concentrations also have large spatial and temporal variations, ranging from 1 to 35 ppbv. The high concentrations of CO are measured with small variations, ranging from 3 to 7 ppmv. The concentrations of VOCs are relatively low, with the total VOC concentrations of less than 6 ppbv. The relative small VOC concentrations and the relative large NO_x concentrations suggest that the O₃ chemical formation is under a strong VOC-limited regime in the YRD region. The measured O₃ and NO_x concentrations are strongly anti-correlated, indicating that enhancement in NO_x concentrations leads to decrease in O₃ concentrations. Moreover, the O₃ concentrations are more sensitive to NO_x concentrations in the rural region than in the city region. The ratios of Δ[O₃]/Δ[NO_x] are ?2.3 and ?0.25 in the rural and in the city region, respectively. In addition, the measured NO_x and SO₂ concentrations are strongly correlated, highlighting that the NO_x and SO₂ are probably originated from same emission sources. Because SO₂ emissions are significantly originated from coal burnings, the strong correlation between SO₂ and NO_x concentrations suggests that the NO_x emission sources are mostly from coal burned sources. As a result, the future automobile increases could lead to rapid enhancements in O₃ concentrations in the YRD region.     

An empirical approach for the prediction of annual mean nitrogen dioxide concentrations in London

Annual mean limits for NO₂ concentrations have been set in the European Union, which will be most challenging to meet in large urban conurbations. In this paper, we discuss techniques that have been developed to predict current and future NO₂ concentrations in London, utilising ambient data. Hourly average NO_x (NO+NO₂) and NO₂ concentrations are used to calculate NO_x frequency distributions. By defining relationships between the annual mean NO_x and NO₂ at different sites, it is possible to investigate different NO_x reduction strategies. The application of the frequency distribution approach to monitoring sites in London shows that given the likely change in emissions by 2005, it is unlikely that much of central and inner London will meet the objective. The approaches used suggest that meeting the objective in central London will be the most challenging for policy makers requiring NO_x concentrations as low as 30 ppb, compared with values closer to 36–40 ppb for outer London. Predictions for 2005 indicate that concentrations of NO₂ up to 6 ppb in excess of the objective are likely in central London.     

Influence of boundary conditions on CMAQ simulations over the Iberian Peninsula

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 PM_2.5) 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 PM_2.5 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.     

Evaluation of the CAR-FMI model against measurements near a major road

A field measurement campaign was conducted near a major road in southern Finland from September 15 to October 30, 1995. The concentrations of NO, NO₂ and O₃ were measured simultaneously at three locations, at three heights (3.5, 6 and 10 m) on both sides of the road. Traffic densities and relevant meteorological parameters were also measured on-site. We have compared measured concentration data with the predictions of the road network dispersion model CAR-FMI, used in combination with a meteorological pre-processing model MPP-FMI. In comparison with corresponding results presented previously in the literature, the agreement of measured and predicted datasets was good, as measured using various statistical parameters. For all data (N=587), the index of agreement (IA) was 0.83, 0.82 and 0.89 for the measurements of NO_x, NO₂ and O₃, respectively. The IA is a statistical measure of the correlation of the predicted and measured time series of concentrations. However, the modelling system overpredicts NO_x concentrations with a fractional bias FB=+13%, and O₃ concentrations with FB=+8%, while for NO₂ concentrations FB=−2%. We also analyzed the difference between model predictions and measured data in terms of meteorological parameters. Model performance clearly deteriorated as the wind direction approached a direction parallel to the road, and for the lowest wind speeds. The range of variability concerning atmospheric stability, ambient temperature and the amount of solar radiation was modest during the measurement campaign. As expected, no clear dependencies of model performance were therefore detected in terms of these parameters. The experimental dataset is available for the evaluation of other roadside dispersion models.     

Nitrogen oxide fluxes between corn (Zea mays L.) leaves and the atmosphere

In the United States, fertilized corn fields, which make up approximately 5% of the total land area, account for approximately 45% of total soil NO_x emissions. Leaf chamber measurements were conducted of NO and NO₂ fluxes between individual corn leaves and the atmosphere in (1) field-grown plants near Champaign, IL (USA) in order to assess the potential role of corn canopies in mitigating soil–NO_x emissions to the atmosphere, and (2) greenhouse-grown plants in order to study the influence of various environmental variables and physiological factors on the dynamics of NO₂ flux. In field-grown plants, fluxes of NO were small and inconsistent from plant to plant. At ambient NO concentrations between 0.1 and 0.3 ppbv, average fluxes were zero. At ambient NO concentrations above 1 ppbv, NO uptake occurred, but fluxes were so small (14.3±0.0 pmol m⁻² s⁻¹) as to be insignificant in the NO_x inventory for this site. In field-grown plants, NO₂ was emitted to the atmosphere at ambient NO₂ concentrations below 0.9 ppbv (the NO₂ compensation point), with the highest rate of emission being 50 pmol m⁻² s⁻¹ at 0.2 ppbv. NO₂ was assimilated by corn leaves at ambient NO₂ concentrations above 0.9 ppbv, with the maximum observed uptake rate being 643 pmol m⁻² s⁻¹ at 6 ppbv. When fluxes above 0.9 ppbv are standardized for ambient NO₂ concentration, the resultant deposition velocity was 1.2±0.1 mm s⁻¹. When scaled to the entire corn canopy, NO₂ uptake rates can be estimated to be as much as 27% of the soil-emitted NO_x. In greenhouse-grown and field-grown leaves, NO₂ deposition velocity was dependent on incident photosynthetic photon flux density (PPFD; 400–700 nm), whether measured above or below the NO₂ compensation point. The shape of the PPFD dependence, and its response to ambient humidity in an experiment with greenhouse-grown plants, led to the conclusion that stomatal conductance is a primary determinant of the PPFD response. However, in field-grown leaves, measured NO₂ deposition velocities were always lower than those predicted by a model solely dependent on stomatal conductance. It is concluded that NO₂ uptake rate is highest when N availability is highest, not when the leaf deficit for N is highest. It is also concluded that the primary limitations to leaf-level NO₂ uptake concern both stomatal and mesophyll components.     

An empirical model for predicting urban roadside nitrogen dioxide concentrations in the UK

An annual mean concentration of 40 μg m⁻³ has been proposed as a limit value within the European Union Air Quality Directives and as a provisional objective within the UK National Air Quality Strategy for 2010 and 2005, respectively. Emissions reduction measures resulting from current national and international policies are likely to deliver significant reductions in emissions of oxides of nitrogen from road traffic in the near future. It is likely that there will still be exceedances of this target value in 2005 and in 2009 if national measures are considered in isolation, particularly at the roadside. It is envisaged that this `policy gap’ will be addressed by implementing local air quality management to reduce concentrations in locations that are at risk of exceeding the objective. Maps of estimated annual mean NO₂ concentrations in both urban background and roadside locations are a valuable resource for the development of UK air quality policy and for the identification of locations at which local air quality management measures may be required. Maps of annual mean NO₂ concentrations at both background and roadside locations for 1998 have been calculated using modelling methods, which make use of four mathematically straightforward, empirically derived linear relationships. Maps of projected concentrations in 2005 and 2009 have also been calculated using an illustrative emissions scenario. For this emissions scenario, annual mean urban background NO₂ concentrations in 2005 are likely to be below 40 μg m⁻³, in all areas except for inner London, where current national and international policies are expected to lead to concentrations in the range 40–41 μg m⁻³. Reductions in NO_x emissions between 2005 and 2009 are expected to reduce background concentrations to the extent that our modelling results indicate that 40 μg m⁻³ is unlikely to be exceeded in background locations by 2009. Roadside NO₂ concentrations in urban areas in 2005 and 2009 are expected to be significantly higher than in background locations. 21% of urban major road links are expected to have roadside NO₂ greater than or equal to 40 μg m⁻³ in 2005 for our illustrative emissions scenario. The continuing downward trend in traffic emissions is likely to further reduce the number of links exceeding this value by 2009, with about 6% of urban major road links predicted to have concentrations higher than 40 μg m⁻³. The majority of these links are in the London area. The remaining links are generally confined to the most heavily trafficked roads in other big cities.     

Surface ozone and NOx concentrations at a high altitude Mediterranean site,Greece

Ozone was measured in six- and NO_x in five sampling periods in 1996–97, mostly during summer, at a 1070 m altitude site in northern Peloponnese. Mean values in each sampling period ranged from 43–48 ppb exceeding the European Union 24 h plant protection standard. The background ozone concentration of 43 ppb derived from the correlation of ozone with NO^′_x also exceeded the EU plant protection standard. Ozone exhibited maxima in the afternoon and minima during the night; in certain 24–48 h periods, however, the ozone concentrations remained practically constant; in these short periods air mass back trajectories indicated air masses which originated in north Africa. NO^′_x concentrations had maximum of 24 h around noon. Their mean concentrations ranged from 0.5–0.7 ppb, smaller than respective concentrations in north-central Europe.     

Kinetics of the gas-phase reactions of NO3 radicals with ethyl acrylate,n-butyl acrylate,methyl methacrylate and ethyl methacrylate

The relative rate method has been used to determine the rate constants for the gas-phase reactions of NO₃ radicals with a series of acrylate esters: ethyl acrylate (k₁), n-butyl acrylate (k₂), methyl methacrylate (k₃) and ethyl methacrylate (k₄) at 298 ± 1 K and 760 Torr. The obtained rate constants are k₁ = (1.8 ± 0.25) × 10^?16 cm³ molecule^?1 s^?1, k₂ = (2.1 ± 0.33) × 10^?16 cm³ molecule^?1 s^?1, k₃ = (3.6 ± 1.2) × 10^?15 cm³ molecule^?1 s^?1, k₄ = (4.9 ± 1.7) × 10^?15 cm³ molecule^?1 s^?1. The experimental rate constants are in good agreement with theoretical rate constants calculated by an algorithm of the correlation between the rate constants and the orbital energies for the reactions of unsaturated VOCs with NO₃ radicals. In addition, the atmospheric lifetimes of the compound against NO₃ attack are estimated and the results show that NO₃ reactions contribute little to the atmospheric losses of acrylate esters except in polluted regions.     

A simple technique for measuring power station SO2 and NO2 emissions

Emissions of SO₂ and NO₂ from fossil fuel power stations can have serious environmental consequences via conversion to sulphuric and nitric acids and subsequent deposition. Consequently, there is considerable interest in techniques capable of monitoring these emissions, in order to ensure compliance with environmental legislation. Here we present a novel approach to measuring power station SO₂ and NO₂ emissions by traversing underneath the plume by car or on-foot or scanning the power station's plume from a fixed position with a compact and lightweight UV spectrometer. This work was performed at a power station in eastern England during January, February and June 2003, resulting in a SO₂ flux of 5.2 kg s⁻¹, which is in close correspondence with the in-stack measured value of 5.3 kg s⁻¹. This technique is considerably simpler and cheaper than other remote sensing approaches to monitoring these emissions.     

Verification of a source-oriented externally mixed air quality model during a severe photochemical smog episode

The CIT/UCD three-dimensional source-oriented externally mixed air quality model is tested during a severe photochemical smog episode (Los Angeles, 7–9 September 1993) using two different chemical mechanisms that describe the formation of ozone and secondary reaction products. The first chemical mechanism is the secondary organic aerosol mechanism (SOAM) that is based on SAPRC90 with extensions to describe the formation of condensable organic products. The second chemical mechanism is the caltech atmospheric chemistry mechanism (CACM) that is based on SAPRC99 with more detailed treatment of organic oxidation products.The predicted ozone concentrations from the CIT/UCD/SOAM and the CIT/UCD/CACM models agree well with the observations made at most monitoring sites with a mean normalized error of approximately 0.4–0.5. Good agreement is generally found between the predicted and measured NO_x concentrations except during morning rush hours of 6–10 am when NO_x concentrations are under-predicted at most locations. Total VOC concentrations predicted by the two chemical mechanisms agree reasonably well with the observations at three of the four sites where measurements were made. Gas-phase concentrations of phenolic compounds and benzaldehyde predicted by the UCD/CIT/CACM model are higher than the measured concentrations whereas the predicted concentrations of other aromatic compounds approximately agree with the measured values.The fine airborne particulate matter mass concentrations (PM_2.5) predicted by the UCD/CIT/SOAM and UCD/CIT/CACM models are slightly greater than the observed values during evening hours and lower than observed values during morning rush hours. The evening over-predictions are driven by an excess of nitrate, ammonium ion and sulfate. The UCD/CIT/CACM model predicts higher nighttime concentrations of gaseous precursors leading to the formation of particulate nitrate than the UCD/CIT/SOAM model. Elemental carbon and total organic mass are under-predicted by both models during morning rush hour periods. When this latter finding is combined with the NO_x under-predictions that occur at the same time, it suggests a systematic bias in the diesel engine emissions inventory. The mass of particulate total organic carbon is under-predicted by both the UCD/CIT/SOAM and UCD/CIT/CACM models during afternoon hours. Elemental carbon concentrations generally agree with the observations at this time. Both the UCD/CIT/SOAM and UCD/CIT/CACM models predict low concentrations of secondary organic aerosol (SOA) (<3.5 μg m⁻³) indicating that both models could be missing SOA formation pathways. The representation of the aerosol as an internal mixture vs. a source-oriented external mixture did not significantly affect the predicted concentrations during the current study.     

The impact of an 8 h ozone air quality standard on ROG and NOx controls in Southern California

The new National Ambient Air Quality Standard for ozone in the US uses 8 h averaging for the concentration. Based on the 1993 ambient data for Southern California, 8 h averaging has a moderate tendency to move the location of the peak ozone concentration east of the location of the peak 1 h ozone concentration. Reducing the area-wide peak 8 h ozone concentration to 80 ppb would require an effective reduction of the area-wide peak 1 h ozone concentration to around 90 ppb. The Urban Airshed Model with improved numerical solvers, meteorological input based on a mesoscale model and an adjusted emissions inventory was used to study the effect of reactive organic gases (ROG) and NO_x controls on daily-maximum and peak 8 h ozone concentrations under the 26–28 August 1987 ozone episodic conditions in Southern California. The NO_x disbenefit remains prominent for the case of 8 h ozone concentration but is somewhat less prominent, especially when areal ozone exposure is considered, than the case for 1 h ozone concentration. The role of two indicators – O₃/NO_y and H₂O₂/HNO₃ – for NO_x- and ROG-sensitivity for 1 and 8 h ozone concentrations were also studied. In general, the indicator trends are consistent with model predictions, but the discriminating power of the indicators is rather limited.     

Phosphine in the marine atmosphere along a hemispheric course from China to Antarctica

The gas phosphine (PH₃) is a part of an atmospheric link of the phosphorus cycle on earth. Previous research reported the terrestrial lower tropospheric PH₃ at night in the 1 ng m⁻³ range in remote areas, with the peak of 100 ng m⁻³ in populated areas, and at daytime even lower concentrations in the pg m⁻³ range. The data of the global marine atmospheric PH₃ are still very sparse.This study presents surprisingly high concentrations of PH₃ in the order of 0.1–1 μg m⁻³ in many of 32 samples of the marine atmosphere in the latitudinal range from 30°N to 65°S (the cruise of research ship Xuelong from Shanghai Harbor, China, to Antarctica). The highest concentrations were measured near coastal areas of Eastern Asia and Western Australia. A significant correlation exists between marine atmospheric PH₃ concentration and air temperature at 22:00 (local time). PH₃ concentrations at different latitudes strongly decline with daylight intensity according to a logarithmic relationship. These surprisingly high concentrations of the readily oxidizable PH₃ in the air indicate hitherto unknown but important PH₃ emission sources in marine environment. More work is necessary to evaluate the sources of atmospheric PH₃ from marine biosphere.     

FT-IR product study of the OH-initiated oxidation of DMS in the presence of NOx

The influence of NO_x (NO+NO₂) concentrations on the product distribution of the OH-initiated oxidation of DMS has been studied at room temperature using total NO_x concentrations varying from 0 to ∼1800 ppbv (30–600 ppbv NO₂ and 140–1760 ppbv NO). Clear trends in the formation yields of the products SO₂, COS, MSA, MTF (methyl thiolformate), MSPN (methanesulphonyl peroxynitrate), DMSO and DMSO₂ have been observed with variation in NO_x. The presence of low levels of NO reduces the yields of both MTF and COS to zero. The formation yields of MSA and DMSO₂ increase with increasing NO_x concentration, whereas the yields of DMSO and SO₂ decrease. The following approximate changes in the yield, not corrected for possible loss processes, have been measured for variation of NO_x between 0 and ∼1800 ppbv: DMSO decreases from 20 to 3%S; DMSO₂ increases from 3 to 15%S, SO₂ decreases from 70 to 30%S and MSA increases from 4 to 17%S. Under the experiments conditions NO_x levels of several tens of ppbv are required before a perceptible change is observed in the MSA yield. If applicable to the atmosphere such a situation is only likely to be observed near coastal areas affected by pollution. MSPN (CH₃SO₂O₂NO₂) is observed as an oxidation product in the presence of NO₂ even at low levels (e.g. 60 ppbv). Its possible role as a NO_x reservoir in the troposphere is considered.