Ozone pollution and ozone biomonitoring in European cities. Part I: Ozone concentrations and cumulative exposure indices at urban and suburban sites

In the frame of a European research project on air quality in urban agglomerations, data on ozone concentrations from 23 automated urban and suburban monitoring stations in 11 cities from seven countries were analysed and evaluated. Daily and summer mean and maximum concentrations were computed based on hourly mean values, and cumulative ozone exposure indices (Accumulated exposure Over a Threshold of 40 ppb (AOT40), AOT20) were calculated. The diurnal profiles showed a characteristic pattern in most city centres, with minimum values in the early morning hours, a strong rise during the morning, peak concentrations in the afternoon, and a decline during the night. The widest amplitudes between minimum and maximum values were found in central and southern European cities such as Düsseldorf, Verona, Klagenfurt, Lyon or Barcelona. In the northern European cities of Edinburgh and Copenhagen, by contrast, maximum values were lower and diurnal variation was much smaller. Based on ozone concentrations as well as on cumulative exposure indices, a clear north–south gradient in ozone pollution, with increasing levels from northern and northwestern sites to central and southern European sites, was observed. Only the Spanish cities did not fit this pattern; there, ozone levels were again lower than in central European cities, probably due to the direct influence of strong car traffic emissions. In general, ozone concentrations and cumulative exposure were significantly higher at suburban sites than at urban and traffic-exposed sites. When applying the newly established European Union (EU) Directive on ozone pollution in ambient air, it was demonstrated that the target value for the protection of human health was regularly surpassed at urban as well as suburban sites, particularly in cities in Austria, France, northern Italy and southern Germany. European target values and long-term objectives for the protection of vegetation expressed as AOT40 were also exceeded at many monitoring sites.     

Assessment of present and future risk to Italian forests and human health: Modelling and mapping

A review of ozone pollution in Italy shows levels largely above the thresholds established by EU regulation for vegetation and human health protection. The Italian air quality monitoring network appears quantitatively inadequate to cover all the territorial surface, because of scarcity and unequal distribution of monitoring sites. By applying the integrated assessment model RAINS-Italy to the year 2000, the whole of Italy exceeds the AOT40 critical level for forest, while Northern and central areas show strong potential of O₃ impact on human health with ∼11% of territory >10 O₃-induced premature deaths. Two scenarios for the year 2020, the Current Legislation and the Maximum Technical Feasible Reduction, show a reduction of AOT40Forest by 29% and 44%, SOMO35 by 31% and 47%, and O₃-induced premature deaths by 32% and 48%, compared to 2000. RAINS-Italy can be used to improve the map quality and cover areas not reached by the national monitoring network.     

How to select the best tree planting locations to enhance air pollution removal in the MillionTreesNYC initiative

Highest priority zones for tree planting within New York City were selected by using a planting priority index developed combining three main indicators: pollution concentration, population density and low canopy cover. This new tree population was projected through time to estimate potential air quality and carbon benefits. Those trees will likely remove more than 10 000 tons of air pollutants and a maximum of 1500 tons of carbon over the next 100 years given a 4% annual mortality rate. Cumulative carbon storage will be reduced through time as carbon loss through tree mortality outweighs carbon accumulation through tree growth. Model projections are strongly affected by mortality rate whose uncertainties limit estimations accuracy. Increasing mortality rate from 4 to 8% per year produce a significant decrease in the total pollution removal over a 100 year period from 11 000 tons to 3000 tons.     

Ozone fluxes over various plant ecosystems in Italy: A review

Among air pollutants, ozone is the most important stressor to vegetation, which undergoes damage and biomass reduction after penetration of ozone molecules into the leaf tissues through the stomata. Stomatal ozone fluxes are considered the governing factor needed to assess risk to plant health due to ozone. Although this parameter may be calculated by modeling, direct measurements are scarce. Moreover, southern European situations, especially regarding Italy, require special attention due to the decoupling between ozone concentrations and fluxes. This work reviews ozone flux measurements made during the last 15 years through Italy.     

Climatology and forecast modeling of ambient carbon monoxide in Phoenix, Arizona

We perform a climatology of factors influencing ambient carbon monoxide (CO), in which we examine the relationships between meteorology, traffic patterns, and CO at seasonal, weekly, and diurnal time scales in Phoenix, Arizona. From this analysis we identify a range of potentially important variables for statistical CO modeling. Using stepwise multivariate regression, we create a suite of models for hourly and 8-h ambient CO designed for daily operational forecasting purposes. The resulting models include variables and interaction terms related to anticipated nocturnal atmospheric stability as well as antecedent and climatological CO behavior. The models are evaluated using a range of error statistics and skill measures. The most successful approach employs a two-stage modeling strategy in which an initial prediction is made that may, depending on the forecast value, be followed by a second prediction that improves upon the first. The best models provide accurate daily forecasts of CO, with explained variances approaching 0.9 and errors under 1 ppm.     

Ozone exposure and stomatal sluggishness in different plant physiognomic classes

Gas exchange responses to static and variable light were tested in three species: snap bean (Phaseolus vulgaris, two cultivars), California black oak (Quercus kelloggii), and blue oak (Q. douglasii). The effects of 1-month (snap beans) and 2-month (oaks) O₃ (ozone) exposure (70 ppb over 8 h per day in open-top chambers) were investigated. A delay in stomatal responses (i.e., ‘sluggish’ responses) to variable light was found to be both an effect of O₃ exposure and a reason for increased O₃ sensitivity in snap bean cultivars, as it implied higher O₃ uptake during times of disequilibrium. Sluggishness increased the time to open (thus limiting CO₂ uptake) and close stomata (thus increasing transpirational water loss) after abrupt changes in light level. Similar responses were shown by snap beans and oaks, suggesting that O₃-induced stomatal sluggishness is a common trait among different plant physiognomic classes.     

Evaluation of near surface ozone in air quality simulations forced by a regional climate model over Europe for the period 1991–2000

This study aims to evaluate near surface ozone simulated with the modelling system RegCM3/CAMx against ozone measurements from the EMEP database for the recent decade 1991–2000. The RegCM3/CAMx simulations were performed on a 50 km × 50 km grid over Europe driven either by ERA-40 reanalysis (hereafter referred as ERA simulation) or the global circulation model (GCM) ECHAM5 (hereafter referred as ECHAM simulation). A set of statistical metrics is used for the model evaluation, including temporal correlation coefficient, the ratio of the standard deviations and the bias of simulated versus observed values. Overall, a good agreement is found for both ERA and ECHAM simulations at the majority of the selected EMEP stations in all metrics throughout the year based either on monthly or daily ozone values. Based on these results, it is assessed that the modelling system RegCM3/CAMx is suitable to be used for present and future regional climate-air quality simulations with emphasis on near surface ozone. The ERA simulations reproduce more accurately the observed ozone values in comparison to ECHAM simulations because the meteorology of the ERA experiment is closer to real atmospheric conditions than the GCM based experiment. On a seasonal basis, both ERA and ECHAM simulations exhibit a seasonally dependent bias, with winter and spring ozone values being generally under-estimated by the model and summer and autumn values being slightly overestimated. This seasonally dependent bias is also evident from median and peak midday ozone values. However, the highest observed midday ozone peaks in summer, with values higher than 80 ppbv, could not be captured either by ERA or ECHAM simulations. An analysis of day-time and night-time ERA and ECHAM modelled ozone values shows that CAMx performs better during the day-time.     

Ozone patterns for three metropolitan statistical areas in North Carolina, USA

As part of an effort by the state of North Carolina to develop a State Implementation Plan (SIP) for 1-h peak ozone control, a network of ozone stations was established to monitor surface ozone concentrations across the state. Between 19 and 23 ozone stations made continuous surface measurements between 1993 and 1995 surrounding three major metropolitan statistical areas (MSAs): Raleigh/Durham (RDU), Charlotte/Mecklenburg (CLT), and Greensboro/High Point/Winston-Salem (GSO). Statistical averages of the meteorological and ozone data were performed at each Metropolitan Statistical Area (MSA) to study trends and/or relationships on high ozone days (days in which one of the MSA sites measured an hourly ozone concentration90.0 ppbv). County emission maps of precursor gases, wind roses, total area averages of ozone, total downwind averages of ozone deviations, upwind averages of ozone, and a modified delta ozone analysis were all obtained and analyzed. The results of this study show a reduction in the delta ozone relative to an earlier study at RDU, but no average significant change at CLT (no comparison can be made for GSO). The statistical data analyses in this study are used to quantify the importance of local contributions and regional transport, to ozone air pollution in the MSAs.     

北京城区河湖水系治理中的问题与建议

简要地回顾北京市近20年河湖水系治理历程中所取得的成就，分析存在的一些主要问题，根据对城区雨水径流非点源污染总量的粗略估算，指出城市雨水径流非点源污染是导致整治后的河湖水系水质恶化最主要的污染因素；结合发达国家对河湖水系治理的一些经验对北京市河湖水系的治理提出几点建议，以期为彻底治理河湖水系的污染提供新的思路，也可供其他城市在治理城市水系污染时参考。     

Ozone distribution and phytotoxic potential in mixed conifer forests of the San Bernardino Mountains, southern California

In the San Bernardino Mountains of southern California, ozone (O(3)) concentrations have been elevated since the 1950s with peaks reaching 600ppb and summer seasonal averages >100ppb in the 1970s. During that period increased mortality of ponderosa and Jeffrey pines occurred. Between the late 1970s and late1990s, O(3) concentrations decreased with peaks approximately 180ppb and approximately 60ppb seasonal averages. However, since the late 1990s concentrations have not changed. Monitoring during summers of 2002-2006 showed that O(3) concentrations (2-week averages) for individual years were much higher in western sites (58-69ppb) than eastern sites (44-50ppb). Potential O(3) phytotoxicity measured as various exposure indices was very high, reaching SUM00 - 173.5ppmh, SUM60 - 112.7ppmh, W126 - 98.3ppmh, and AOT40 - 75ppmh, representing the highest values reported for mountain areas in North America and Europe.     

Ozone flux over a Norway spruce forest and correlation with net ecosystem production

Daily ozone deposition flux to a Norway spruce forest in Czech Republic was measured using the gradient method in July and August 2008. Results were in good agreement with a deposition flux model. The mean daily stomatal uptake of ozone was around 47% of total deposition. Average deposition velocity was 0.39 cm s⁻¹ and 0.36 cm s⁻¹ by the gradient method and the deposition model, respectively. Measured and modelled non-stomatal uptake was around 0.2 cm s⁻¹. In addition, net ecosystem production (NEP) was measured by using Eddy Covariance and correlations with O₃ concentrations at 15 m a.g.l., total deposition and stomatal uptake were tested. Total deposition and stomatal uptake of ozone significantly decreased NEP, especially by high intensities of solar radiation.     

Ozone measurements along vertical transects in the Alps

To investigate the vertical profiles of air pollutants in the boundary layer, aircraft and balloon-born measurements and measurements using a cable car as an instrument platform have been performed in different parts of the Alps. This on-line monitoring of atmospheric pollutants requires expensive and sophisticated techniques. In order to control ambient air quality in remote regions, where no infrastructure like power supply is available, simple instruments are required. The objective of this study, which was coordinated and evaluated by the GSF-Forschungszentrum für Umwelt und Gesundheit was first, to investigate the vertical distribution of ozone in different parts of the Alps and secondly, in addition to continuous analyser measurements, to test monitoring by means of two types of passive samplers. The selection of these samplers — one for one week use and another one for two week application — was based on a passive sampler intercomparison done in a preliminary study one year earlier.     

Long-term variation in surface ozone and its precursors in Athens,Greece

INTENTION, GOAL, SCOPE, BACKGROUND: Photochemical pollution is a very complex process involving meteorological, topographic, emission and chemical parameters. The most important chemical mechanisms involved in the atmospheric process have already been identified and studied. However, many unknown parameters still exist because of the large number of participating chemical reactions. OBJECTIVE: The present study investigates the processes involved in the photochemical pollution effect of an urban station located in the greater area of the Athens basin and gives a plausible explanation for the different seasonal ozone development between that station and another rural one. Furthermore, the distribution of the mean monthly surface ozone observed at the urban station during 1987-2001 is examined in order to create a relevant forecasting tool. METHODS: Averaged hourly data of O3 and NOx observations monitored at the above mentioned stations, during 1987-2001, have been used in order to derive the daytime (7:00-15:00) values. Trajectories calculated by using a 2D-trajectory code and meteorological data, during the period 1988-1996, have also been used. RESULTS AND DISCUSSION: At the urban station, the percentage negative trend of NO and NOx data in winter and summer is higher than that in spring and autumn, while the percentage ozone trend is maximum in the summer. On the contrary, the negative surface ozone trend at the rural station exhibits a minimum in summer and a maximum in autumn and winter. The mean seasonal wind-rose for the selected months shows that the northward wind flow dominates during June, the month of the lowest negative ozone trend in the rural station. Finally, the development of the forecasting tool shows that the mean monthly surface ozone data during the period (1987-2001) demonstrates a semi-log distribution. CONCLUSIONS: Air transport effect on the air pollution of the rural station (not blocked by mountains) is deduced as a possible reason for the different seasonal ozone development observed between the rural and the urban station. Finally, the discrepancies between the theoretical probabilities deduced by the model and the empirical ones appear to be very small, and the corresponding correlation coefficient is 0.99. RECOMMENDATION AND OUTLOOK: However, to interpret the aforementioned statistical results about the negative trends in ozone and its precursors, additional parameters can be taken into account. Changes in NOx concentrations, for instance, can result not only from changes in emissions or meteorological conditions. There might also be a contribution through changes in the atmospheric composition. A study of the contribution of changes in atmospheric composition to trends of observed NOx concentrations requires that a series of steps be taken (removal of meteorological influence in the time series, calculation of trends in OH concentrations, etc.).     

Distribution of polycyclic aromatic hydrocarbons in urban stormwater in Queensland, Australia

This paper reports the distribution of Polycyclic Aromatic Hydrocarbons (PAHs) in wash-off in urban stormwater in Gold Coast, Australia. Runoff samples collected from residential, industrial and commercial sites were separated into a dissolved fraction (<0.45 μm), and three particulate fractions (0.45-75 μm, 75-150 μm and >150 μm). Patterns in the distribution of PAHs in the fractions were investigated using Principal Component Analysis. Regardless of the land use and particle size fraction characteristics, the presence of organic carbon plays a dominant role in the distribution of PAHs. The PAHs concentrations were also found to decrease with rainfall duration. Generally, the 1- and 2-year average recurrence interval rainfall events were associated with the majority of the PAHs and the wash-off was a source limiting process. In the context of stormwater quality mitigation, targeting the initial part of the rainfall event is the most effective treatment strategy. The implications of the study results for urban stormwater quality management are also discussed.     

Impact of the global economic crisis on metal levels in particulate matter (PM) at an urban area in the Cantabria Region (Northern Spain)

Air pollution by particulate matter is well linked with anthropogenic activities; the global economic crisis that broke out in the last year may be a proper indicator of this close relationship. Some economic indicators show the regional effects of the crisis on the Cantabria Region. The present work aims to evaluate the impact of the economic crisis on PM10 levels and composition at the major city of the region, Santander. Some metals linked to anthropogenic activities were measured at Santander and studied by Positive Matrix Factorization; this statistical analysis allowed to identify three main factors: urban background, industrial and molybdenum-related factor. The main results show that the temporal trend of the levels of the industrial tracers found in the present study are well agree with the evolution of the studied economic indicators; nevertheless, the urban background tracers and PM10 concentration levels are not well correlated with the studied economic indicators.     

EuroBionet: a pan-European biomonitoring network for urban air quality assessment

EuroBionet, the 'European Network for the Assessment of Air Quality by the Use of Bioindicator Plants', is an EU-funded cooperative project currently consisting of public authorities and scientific institutes from 12 cities in 8 countries. In 2000, the bioindicator plants tobacco (Nicotiana tabacum Bel W3), poplar (Populus nigra 'Brandaris'), spiderwort (Tradescantia sp. clone 4430), Italian rye grass (Lolium multiflorum italicum) and curly kale (Brassica oleracea acephala) were exposed to ambient air at 90 monitoring sites according to standardised methods. Visible injuries and growth parameters were assessed and the accumulation of toxic substances in leaves determined. The exposure of tobacco resulted in a gradient with low levels of ozone-induced foliar injury in N and NW Europe, and medium to high values in the southern and central regions. The results of heavy metal and sulphur analyses in rye grass samples generally showed low to very low sulphur and low to medium heavy metal concentrations in leaves. In some cities, however, local hot spots of heavy metal contamination were detected. Analyses of the PAH contents in curly kale leaves gave low to medium values, with locally elevated levels at traffic-exposed sites.     

Measurement of total OH reactivity by laser-induced pump and probe technique—comprehensive observations in the urban atmosphere of Tokyo

Total OH reactivity was observed by use of the laser-induced pump and probe technique, and the urban air quality in Tokyo was diagnosed comprehensively. The concentrations of NO_x, CO, O₃, non-methane hydrocarbons (NMHCs) and oxygenated volatile organic compounds (OVOCs) were observed simultaneously. The observations were conducted in July and August 2003, and in January, February, May, and November 2004. Generally, the observed OH reactivity was higher than the calculated values derived using the observed concentrations of the trace species. The differences between the observed and calculated values in summer, spring, and autumn were approximately 30%. However, the difference in winter was smaller than those in the other seasons. In addition, while the differences observed in summer, spring, and autumn correlated with the total reactivity of the OVOCs (Σ_i k_OVOCi[OVOC_i](s⁻¹), k_i is rate constant of its compounds with OH), the correlations were not confirmed in the case of winter because atmospheric oxidation was less active and OVOCs levels were low in winter. These results suggest that the secondary products of the photochemical reactions in the atmosphere would be a missing sink for the OH loss process in the urban area.