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Trees have the potential to improve urban air quality as leaves and needles capture air pollutants from the air, but further empirical data has been requested to quantify these effects. We measured the concentration of 32 poly-cyclic aromatic hydrocarbons (PAHs) in leaves of pin oak (Quercus palustris) and needles of black pine (Pinus nigra) in the City of Gothenburg, Sweden, during the summer of 2018. Oak leaves were collected twice (June, Sep-tember), while one-year-old (C + 1) and three-year-old (C + 3) pine needles were sampled in June to study the temporal development of leaf/needle PAH concentrations. Specific leaf area (SLA) was estimated, which permit-ted calculation of leaf/needle area-based PAH content that were compared with the mass-based concentration. In addition, the air concentration of PAHs and NO2 was measured using passive samplers. There was a strong correlation between air concentrations of PAH and NO2, indicating that the pollutants to a large degree originate from the same sources. In the oak leaves there was a significant decrease in low molecular mass PAHs (L-PAH, mainly gaseous) between June and September, but a significant increase in high molecular mass PAHs (H-PAH, mainly particle-bound). There was a strong correlation between L-PAH concentration in leaves and in air indicating an influence of equilibrium processes between ambient air and leaf. In the pine needles, there was a significant increase of both L-PAH and H-PAH in three-year-old needles compared to one-year-old needles. Pine was superior to oak in accumulating PAHs from the air, especially for L-PAHs when comparing area-based content. However, H-PAH concentrations were higher in oak leaves compared to pine needles on a leaf mass basis, emphasizing the importance of how concentrations are expressed. The results from this study can contribute to the development of urban planning strategies regarding the effect of vegetation on air quality. (C) 2021 The Authors. Published by Elsevier B.V.

Ongoing urban exploitation is increasing pressure to transform urban green spaces, while there is increasing awareness that greenery provides a range of important benefits to city residents. In efforts to help resolve associated problems we have developed a framework for integrated assessments of ecosystem service (ES) benefits and values provided by urban greenery, based on the ecosystem service cascade model. The aim is to provide a method for assessing the contribution to, and valuing, multiple ES provided by urban greenery that can be readily applied in routine planning processes. The framework is unique as it recognizes that an urban greenery comprises several components and functions that can contribute to multiple ecosystem services in one or more ways via different functional traits (e.g. foliage characteristics) for which readily measured indicators have been identified. The framework consists of five steps including compilation of an inventory of indicator; application of effectivity factors to rate indicators' effectiveness; estimation of effects; estimation of benefits for each ES; estimation of the total ES value of the ecosystem. The framework was applied to assess ecosystem services provided by trees, shrubs, herbs, birds, and bees, in green areas spanning an urban gradient in Gothenburg, Sweden. Estimates of perceived values of ecosystem services were obtained from interviews with the public and workshop activities with civil servants. The framework is systematic and transparent at all stages and appears to have potential utility in the existing spatial planning processes.

Air pollution levels (NO2, PAHs, O3) were investigated, before (BLE) and after (ALE) leaf emergence, in the urban landscape of Gothenburg, Sweden. The aims were to study the 1) spatial and temporal variation in pollution levels between urban green areas, 2) effect of urban vegetation on air pollution levels at the same distance from a major emission source (traffic route), 3) improvement of urban air quality in urban parks compared to adjacent sites near traffic, 4) correlation between air pollution and noise in a park. O3 varied little over the urban landscape. NO2 varied strongly and was higher in situations strongly influenced by traffic. Four PAH variables were included: total PAH, total particle-bound PAH, the quantitatively important gaseous phenanthrene and the highly toxic particle-bound benzo(a)pyrene. The variation of PAHs was similar to NO2, but for certain PAHs the difference between highly and less polluted sites was larger than for NO2. At a vegetated site, NO2 and particulate PAH levels were lower than at a non-vegetated site at a certain distance from a busy traffic route. This effect was significantly larger ALE compared to BLE for NO2, indicating green leaf area to be highly significant factor for air quality improvement. For particulate PAHs, the effect was similar BLE and ALE, indicating that tree bark and branches also could be an important factor in reducing air pollution. Parks represented considerably cleaner local environments (park effect), which is likely to be a consequence of both a dilution (distance effect) and deposition. Noise and air pollution (NO2 and PAH) levels were strongly correlated. Comparison of noise levels BLE and ALE also showed that the presence of leaves significantly reduced noise levels. Our results are evidence that urban green spaces are beneficial for urban environmental quality, which is important to consider in urban planning.

This review summarizes new information on the current status of ground-level ozone in Europe north of the Alps. There has been a re-distribution in the hourly ozone concentrations in northern Europe during 1990–2015. The highest concentrations during summer daytime hours have decreased while the summer night-time and winter day- and night-time concentrations have increased. The yearly maximum 8-h mean concentrations ([O 3 ] 8h,max ), a metric used to assess ozone impacts on human health, have decreased significantly during 1990–2015 at four out of eight studied sites in Fennoscandia and northern UK. Also the annual number of days when the yearly [O 3 ] 8h,max exceeded the EU Environmental Quality Standard (EQS) target value of 60 ppb has decreased. In contrast, the number of days per year when the yearly [O 3 ] 8h,max exceeded 35 ppb has increased significantly at two sites, while it decreased at one far northern site. [O 3 ] 8h,max is predicted not to exceed 60 ppb in northern UK and Fennoscandia after 2020. However, the WHO EQS target value of 50 ppb will still be exceeded. The AOT40 May–July and AOT40 April–September metrics, used for the protection of vegetation, have decreased significantly at three and four sites, respectively. The EQS for the protection of forests, AOT40 April–September 5000 ppb h, is projected to no longer be exceeded for most of northern Europe sometime before the time period 2040–2059. However, if the EQS is based on Phytotoxic Ozone Dose (POD), POD 1 , it may still be exceeded by 2050. The increasing trend for low and medium range ozone concentrations in combination with a decrease in high concentrations indicate that a new control strategy, with a larger geographical scale than Europe and including methane, is needed for ozone abatement in northern Europe.

Ozone concentrations ([O3]) and meteorological parameters were measured with a mobile monitoring station at two coastal and five inland sites in southwest Sweden. Three of the five inland sites were located topographically low and two high compared to the surrounding landscape. In addition, [O3] data from six permanent monitoring stations in southern Sweden were analysed in relation to the positions of the measurement sites in the landscape. [O3] was also measured with passive diffusion samplers at two other sites. Both the diurnal temperature range (DTR) and the diurnal [O3] range (DOR) were to a large extent explained by the strength of the nocturnal temperature inversions at the sites. To investigate the influence of topography, the relative altitude of the sites was defined as the average altitude within a 3 km radius subtracted from the altitude of the site. Statistically significant relationships were obtained for average [O3] as well as DOR with relative altitude. Inland low sites experienced stronger nocturnal temperature inversions, lower average [O3] and larger DOR compared to inland high and coastal sites. Relative altitude was found to be superior to site altitude in explaining the variation of average [O3] and DOR in the landscape. This study underlines the importance of including local topography, as well as vicinity to the coast, in modelling [O3] and in O3 environmental risk assessments.

The North Atlantic Oscillation (NAO), a measure of the strength of the zonal wind across the North Atlantic Ocean, strongly influences weather conditions in NW Europe, e.g. temperature, precipitation and wind, especially during winter. It was hypothesised that elevated concentrations of nitrogen oxides in Gothenburg would be enhanced during negative NAO index (NAOI) conditions, representing more anticyclonic weather situations and thus leading to limited air mixing in the urban atmosphere, than situations with NAOI > 0. Hourly wintertime (December–February) concentrations (1997–2006) of NO2, NO, air pressure, temperature and wind direction from an urban rooftop (30 m above street level) in the centre of the City of Gothenburg were analysed in relation to NAOI. Air pressure, the average concentration of nitrogen oxides (NOx = NO2 + NO), as well as the fraction of hourly NO2 and NO concentrations exceeding 90 μg m−3 and the fraction of daily NO concentrations exceeding 60 μg m−3, were significantly and negatively related to NAOI. Air temperature was positively correlated with NAOI. Southerly and westerly winds were more common in months with positive NAOI, while easterly and northerly winds were overrepresented in months with negative NAOI. High pollution concentrations dominantly occurred in situations with northerly and easterly wind directions. High NO2 and NO concentrations were associated with negative NAOI, especially in the morning when the traffic rush coincided with restricted air mixing. Over the ten-year period there were trends for more negative NAOI and increased time fractions with hourly NO2 concentrations exceeding 90 μg m−3. The conclusion of this study is that a climate shift towards higher or lower NAOI has the potential to significantly influence urban air pollution in North-West Europe, and thus the possibility to reach air quality standards, even if emissions remain constant.

Ozone was measured using passive diffusion samplers at alpine Latnjajaure (980 m above sea level [asl]) in the northern Scandian Mountain Range during spring and summer 2006–2008, and year-round at three further sites in northernmost Sweden 2004–2008. These observations were compared with ozone concentrations from three permanent monitoring stations using ultraviolet absorption instruments. Ozone concentrations at Latnjajaure were higher than at the closest monitoring site, illustrating the importance of high elevation for ozone. At the northern sites the ozone spring peak was more pronounced, higher, and earlier (April maximum) compared to a site in south Sweden (May maximum). During summer, ozone concentrations were higher in south Sweden. Presently, the growing season largely starts after the ozone spring peak in north Sweden but is likely to start earlier in the future climate. This could lead to an increased risk for ozone effects on vegetation if the current yearly ozone cycle persists.

Surface ozone concentration and surface air temperature was measured hourly at three coastal sites, four low elevation inland sites and two high elevation inland sites in southwestern Sweden. Diurnal ozone concentration range (DOR) and diurnal temperature range (DTR) were strongly correlated, both spatially and temporally, most likely because both depended on atmospheric stability. Accumulated ozone exposure above a threshold concentration of x nmol mol(-1) (AOTx) was estimated from time-integrated ozone concentration (as from diffusive sampling) and measures of ozone concentration variability. Two methods both estimated 24-h AOTx with high accuracy (modelling efficiencies >90% for x

Concentrations of NO2, NO, and O3 from a rooftop monitoring station in Gothenburg, Sweden (2002–2006) were analysed to characterise NO2 pollution. [NO2] was shown to correlate strongly and non-linearly with [NO x ] (NO x = NO + NO2), in line with observations in other cities. The [NO2] to [NO x ] fraction fell initially with increasing [NO x ]. At [NO x ] levels >200 ppb, the decline in [NO2]/[NO x ] with increasing [NO x ] levelled out and [NO2]/[NO x ] converged towards approximately 0.15–0.16, independent of [NO x ]. Data from a traffic route site showed the same pattern. This value of [NO2]/[NO x ] at high [NO x ] can be interpreted as the NO2 fraction of the NO x emissions from vehicle exhaust. Situations with high NO x pollution and minimum [NO2]/[NO x ] were always associated with [O3] close to zero. Plotting [Ox] (Ox = NO2 + O3) vs. [NO x ] provided a strong linear correlation for situations dominated by local pollution ([NO]/[NO2]>1). The slope of the regression, a measure of the primary NO2 fraction in NO x emissions, was 0.13 during the day and 0.14 during the night. With stronger winds, the rooftop monitoring station became more similar, in terms of NO2 pollution, to a city street site and a traffic route site, although [NO2] was almost always higher at the street/traffic route locations. The EU standard for the annual average of [NO2] (40 μg m−3) was exceeded, while the hourly standard (200 μg m−3, not to be exceeded more than 18 times per year by 2010) was not exceeded at any of the sites.

The impacts of changes in ozone precursor emissions as well as climate change on the future ozone exposure of the vegetation in Europe were investigated. The ozone exposure is expressed as AOT40 (Accumulated exposure Over a Threshold of 40 ppb O3) as well as PODY (Phytotoxic Ozone Dose above a threshold Y). A new method is suggested to express how the length of the period during the year when coniferous and evergreen trees are sensitive to ozone might be affected by climate change. Ozone precursor emission changes from the RCP4.5 scenario were combined with climate simulations based on the IPCC SRES A1B scenario and used as input to the Eulerian Chemistry Transport Model MATCH from which projections of ozone concentrations were derived. The ozone exposure of vegetation over Europe expressed as AOT40 was projected to be substantially reduced between the periods 1990–2009 and 2040–2059 to levels which are well below critical levels used for vegetation in the EU directive 2008/50/EC as well as for crops and forests used in the LRTAP convention, despite that the future climate resulted in prolonged yearly ozone sensitive periods. The reduction in AOT40 was mainly driven by the emission reductions, not changes in the climate. For the toxicologically more relevant POD1 index the projected reductions were smaller, but still significant. The values for POD1 for the time period 2040–2059 were not projected to decrease to levels which are below critical levels for forest trees, represented by Norway spruce. This study shows that substantial reductions of ozone precursor emissions have the potential to strongly reduce the future risk for ozone effects on the European vegetation, even if concurrent climate change promotes ozone formation.

Spring/summer surface ozone concentrations, [O3], in coastal environments were investigated: (1) by comparison of coastal and inland monitoring stations with data from a small island >5 km off the coast of southwest Sweden, (2) as a gradient from the coast towards inland in southernmost Sweden. Further, results from the chemical transport model MATCH were used to assess the marine influence on [O3]. It was hypothesised that [O3] is higher on the small island compared to the coast, especially during night and in offshore wind. Another hypothesis was that [O3] declines from the coast towards inland. Our hypotheses were based on observations that the deposition velocity of O3 to sea surfaces is lower than to terrestrial surfaces, and that vertical air mixing is stronger in the marine environment, especially during night. The island experienced 10 % higher [O3] compared to the coast. This difference was larger with offshore (15 %) than onshore wind (9 %). The concentration difference between island and coast was larger during night, but prevailed during day and could not be explained by differences in [NO2] between the sites. The difference in [O3] between the island and the inland site was 20 %. Higher [O3] over the sea, especially during night, was reproduced by MATCH. In the gradient study, [O3] declined from the coast towards inland. Both [O3] and [NO2] were elevated at the coast, indicating that the gradient in [O3] from the coast was not caused by NO titration. The conclusions were that surface [O3] in marine environments is higher than in coastal, and higher in coastal than inland areas, especially during night.

The negative impacts of surface ozone (O3) on vegetation are determined by external exposure, leaf gas exchange and plant antioxidant defence capacity, all dependent on climate and CO2 concentrations. In this study the influence of climate change on simulated stomatal O3 uptake of a generic crop and a generic deciduous tree at ten European sites was investigated, using the LRTAP Mapping Manual stomatal flux model. O3 concentrations are calculated by a chemistry transport model (MATCH) for three 30-yr time-windows (1961–1990, 2021–2050, 2071–2100), with constant precursor emissions and meteorology from a regional climate model (RCA3). Despite substantially increased modelled future O3 concentrations in central and southern Europe, the flux-based risk for O3 damage to vegetation is predicted to remain unchanged or decrease at most sites, mainly as a result of projected reductions in stomatal conductance under rising CO2 concentrations. Drier conditions in southern Europe are also important for this result. At northern latitudes, the current parameterisation of the stomatal conductance model suggest O3 uptake to be mainly limited by temperature. This study demonstrates the importance of accounting for the influences by climate and CO2 on stomatal O3 uptake, and of developing their representation in models, for risk assessment involving climate change.

Knowledge about temporal and spatial variations of the O3 and NOx relationship in the urban environment are necessary to assess the exceedance of air quality standards for NO2. Both reliable measurements and validated high-resolution air quality models are important to assess the effect of traffic emission on air quality. In this study, measurements of NO, NO2 and O3 concentrations were performed in Gothenburg, Sweden, during the Göte-2005 campaign in February 2005. The aim was to evaluate the variation of pollutant concentrations in the urban landscape in relation to urban air quality monitoring stations and wind speed. A brief description of the meteorological conditions and the air pollution situation during the Göte-2005 campaign was also given. Furthermore, the Air Pollution Model (TAPM) was used to simulate the NOx-regime close to an urban traffic route and the simulations were compared to the measurements. Important conclusions were that the pollutant concentrations varied substantially in the urban landscape and the permanent monitoring stations were not fully representative for the most polluted environments. As expected, wind speed strongly influenced measured pollutant concentrations and gradients. Higher wind speeds dilute NO2 due to stronger dispersion; while at the same time vertical transport of O3 is enhanced, which produces NO2 through oxidation of NO. The oxidation effect was predominant at the more polluted sites, while the dilution effect was more important at the less polluted sites. TAPM reproduced the temporal variability in pollutant concentrations satisfactorily, but was not able to resolve the situation at the most polluted site, due to the local scale site-specific conditions.

Measurements of ground-level ozone concentrations and meteorology (temperature, vapour pressure deficit (VPD), solar radiation) at the monitoring site Ostad (south-west Sweden) were compared to data from the corresponding grid in the EMEP photo-oxidant model for 1997, 1999 and 2000. The influence of synoptic weather on the agreement between model and measurements was studied. Implications of differences between modelled and observed inputs for ozone flux calculations for wheat and potato were investigated. The EMEP model output of ozone, temperature and VPD correlated well with measurements during daytime. Deviations were larger during the night, especially in calm conditions, attributed to local climatological conditions at the monitoring site deviating from average conditions of the grid. These differences did not lead to significant differences in calculated ozone uptake, which was reproduced remarkably well. The uptake calculations were sensitive to errors in the ozone and temperature input data, especially when including a flux threshold.