Establishing a cause and effect relationship for ambient ozone exposure and tree growth in the forest: progress and an experimental approach

Much has been written about the effects of ambient ozone on tree growth. Cause and effect has been established with seedlings in chambers. Results from multi-year studies with older tree seedlings, in open-top chambers, have been inconclusive, due to chamber effects. Extrapolation of results from chambers to trees in the forest is not possible. Predictive models for forest tree growth reductions caused by ozone have been developed, but not verified. Dendrochronological methods have been used to establish correlations between radial growth reductions in forest trees and ambient ozone exposure. The protective chemical ethylenediurea (EDU) has been used to protect tree seedlings from ozone injury. An experimental approach is advocated here that utilizes forest trees selected for sensitivity and non-sensitivity to ozone, dendrochronological methods, the protective chemical EDU, and monitoring data for ambient ozone, stomatal conductance, soil moisture potential, air temperature, PAR, etc. in long-term investigations to establish cause and effect relationships.

Ground level ozone concentrations at a rural location in northern Spain

A systematic analysis of surface ozone observations at a rural area of the upper Spanish plateau is presented. A near four-year study of ozone concentrations was carried out between February 2000 and October 2003. Diurnal and monthly variations of ozone are studied. The peak concentration levels are obtained between 13:00 and 15:00 GMT and the lowest levels at 4:00 and 5:00 GMT. The highest values together with a slight increase in data variability are found from April to August, when spring and summer maxima are appreciated. The relationship between synoptic-scale atmospheric transport patterns and the maximum ozone concentrations was also examined. Analysis of the 500-hPa synoptic weather patterns revealed that the highest values occur during continental and Atlantic ridges in summer and, to a lesser extent, during troughs in the east-northeast of the Iberian Peninsula in spring. Our approach entailed calculating 3-day isobaric backward air mass trajectories at the observational site sorted on the following main origins: European continent, African continent, Atlantic Ocean and local. The assessment of the results showed the influence of local conditions on the daily maximum ozone concentrations. Moreover, continental air masses provide certain evidence of long-range transport added to the local or regional contribution of the main cities affecting the sampling site. Conversely, Atlantic trajectories show the least contribution to ozone levels.

Study on the formation and transport of ozone in relation to the air quality management and vegetation protection in Tenerife (Canary Islands)

An experimental study on the formation and transport of ozone in ambient air was performed in Tenerife (Canary Islands) in order to investigate the processes affecting ozone levels and air quality. The special features of Tenerife (prevalence of the trade wind pattern (NE), orography and the specific location of the local ozone sources) permit to quantify the role of the 'long-range transport from northern latitudes' versus the 'formation and transport of ozone downwind of the main urban areas' of Tenerife. Levels of O(3), NO(2) and O(X) were monitored in different types of environments to achieve this purpose. The results showed that: (1) upwind of the urban areas ozone is mainly transported from the ocean by trade winds, (2) local ozone titration (by NO) and ozone replenishment from the ocean are the main causes of ozone variations in urban and suburban areas, and (3) photochemical ozone production occurs downwind of the urban areas. Photochemical production causes daylight O(3) and O(X) levels downwind of urban areas to be frequently (60% and 35% days/year, respectively) higher than upwind of the urban sites (O(3) and O(X) excess frequently in the range 5-20 ppbv). Due to the above processes, different daily ozone cycles occur in short distances (<30 km), with maximum O(3) levels during daylight or night depending on the site. Ozone phytotoxicity was assessed by calculating the AOT40 index upwind and downwind of the main urban areas. The critical value for the 5-day-AOT40 index was simultaneously exceeded at the two sites (few times/year) during long-range transport events. During the additional exceedances of the critical value downwind of the urban area, relatively high 5-day-AOT40 values were recorded upwind of the urban site. Thus, long-range transport from northern latitudes may produce relatively high 5-days-AOT40 levels in the oceanic boundary layer. These results are important for the protection of the large number of endemic plants in the Canaries. The conceptual model discussed in this study may be qualitatively applied to other islands which possess features similar to those of Tenerife.

Ambient ozone in forests of the Central and Eastern European mountains

Ambient ozone (O(3)) concentrations in the forested areas of the Central and Eastern European (CEE) mountains measured on passive sampler networks and in several locations equipped with active monitors are reviewed. Some areas of the Carpathian Mountains, especially in Romania and parts of Poland, as well as the Sumava and Brdy Mountains in the Czech Republic are characterized by low European background concentrations of the pollutant (summer season means approximately 30 ppb). Other parts of the Carpathians, especially the western part of the range (Slovakia, the Czech Republic and Poland), some of the Eastern (Ukraine) and Southern (Romania) Carpathians and the Jizerske Mountains have high O(3) levels with peak values >100 ppb and seasonal means approximately 50 ppb. Large portions of the CEE mountain forests experience O(3) exposures that are above levels recommended for protection of forest and natural vegetation. Continuation of monitoring efforts with a combination of active monitors and passive samplers is needed for developing risk assessment scenarios for forests and other natural areas of the CEE Region.