M. R. Ashmore

Critical levels for ozone effects on vegetation in Europe.

The evidence of detrimental effects of ozone on vegetation in Europe, and the need to develop international control policies to reduce ozone exposures which are based on the effects of the pollutant, has led to attempts to define so-called critical levels of ozone above which adverse effects on trees, crops and natural vegetation may occur. This review is a critical assessment of the scientific basis of the concepts used to define critical levels for ozone and identifies the key limitations and uncertainties involved. The review focuses on the Level I critical level approach, which provides an environmental standard or threshold to minimise the effects of ozone on sensitive receptors, but does not seek to quantify the impacts of exceeding the critical level under field conditions. The concept of using the AOT (accumulated exposure over a threshold) to define long-term ozone exposure is demonstrated to be appropriate for several economically important species. The use of 40 ppb (giving the AOT40 index) as a threshold concentration gives a good linear fit to experimental data from open-top chambers for arable crops, but it is less certain that it provides the best fit to data for trees or semi-natural communities. Major uncertainties in defining critical level values relate to the choice of response parameter and species; the absence of data for many receptors, especially those of Mediterranean areas; and extrapolation to field conditions from relatively short-term open-top chamber experiments. The derivation of critical levels for long-lived organisms, such as forest trees, may require the use of modelling techniques based on physiological data from experimental studies. The exposure-response data which have been applied to derive critical levels should not be used to estimate the impacts of ozone over large areas, because of the uncertainties associated with extrapolation from the open-top chamber method, especially for forest trees, and because of spatial variation in atmospheric and environmental conditions, which may alter ozone uptake.

Impacts and fate of experimentally enhanced nitrogen deposition on a British lowland heath

Between 1989 and 1996, nitrogen, in the form of (NH4)2SO4 (7.7 or 15.4 kg ha−1 year−1), was added to experimental plots of Calluna at a lowland dry heath in the south of England. Background deposition at this site was estimated at between 13–18 kg N ha−1 year−1, with experimental additions therefore taking total deposition slightly above the proposed critical nitrogen load for lowland heaths. A destructive harvest, carried out in December 1996, revealed large increases in above-ground growth and litter production in response to nitrogen treatments. Plant, litter and soil nitrogen concentrations were also significantly increased. Higher levels of soil decomposer activity, together with faster turnover of litter in nitrogen-treated plots suggest an effect of treatment additions on rates of internal nitrogen cycling. A nitrogen budget for the site revealed that only a relatively small proportion (14–18%) of the nitrogen additions had been accumulated in plant biomass. A similarly small proportion (10–15%) of the extra nitrogen was stored in the litter layer. Since leaching and denitrification losses were minimal, the bulk of the experimental additions were therefore accumulated within the soil compartment. Although no changes in species composition were seen during this experiment, effects on internal nutrient cycling and soil nitrogen status could be expected to have an impact on the outcome of competition between regenerating Calluna and grass seedlings. The results indicate that use of the standard management practice at this site, involving cutting and removal of only above-ground plant material, whilst essential for the maintenance of a mixed-age Calluna sward, will have only a relatively small impact on nitrogen accumulation within this system. The importance of management in modifying the impact of enhanced nitrogen deposition is discussed in the context of critical loads for healthland systems in the UK.

Air pollution and its impacts on wheat yield in the Pakistan Punjab

A study using open-top chambers ventilated with ambient or charcoal-filtered air in the vicinity of Lahore, Pakistan, has demonstrated a reduction of 46.7% and 34.8% in the grain yield for two cultivars of winter wheat (Triticum aestivum L.). The 6-h daily mean O(3) concentrations were 25-45 nl litre(-1) and on the basis of experience in North America and Europe, reductions in yield in the present study are substantially greater than might be predicted. The reasons for this discrepancy are discussed, together with implications for the suitability of a simple, relatively cheap, open-top chamber system for developing-country studies on the effects of air pollution on crops.

Effects of air pollution on rice yield in the Pakistan Punjab

A study using open-top chambers ventilated with ambient or charcoal filtered air in the vicinity of Lahore, Pakistan demonstrated reductions of 42% and 37% in the grain yield of two cultivars of rice (Oryza sativa L.). This yield reduction was primarily due to the reduction in mean panicle number per plant, although significant effects of filtration on 1000 grain weight and the number of filled grains per panicle were also detected. The 6-h daily mean O(3) concentrations were only 10-20 nl litre(-1) during the monsoon season, but increased to 30-55 nl litre(-1) later in the growing season, while the mean NO(2) concentration during the experiment was 12 nl litre(-1). On the basis of experience in North America and Japan, the reductions in yield in the present study are substantially greater than might be predicted. The reasons for this discrepancy are discussed, together with the implications for effects on rice yield in other regions of south and south-east Asia.

Exposure of commuters to carbon monoxide in Mexico city—I. Measurement of in-vehicle concentrations

Abstract The aims of this study were to determine in-vehicle carbon monoxide (CO) levels in major commuting modes in the Metropolitan Area of Mexico City (MAMC) and to identify the main factors affecting the variation in these CO concentrations. CO concentrations were measured inside public and private transport vehicles during the winter of 1991 in Mexico City. Measurements were taken along several commuting routes, during the morning and evening rush hours. Significant differences in CO concentrations were found between different transport modes. The highest CO concentrations were found inside autos and collective taxis, while metro trains, trolleybuses and buses had lower concentrations. In-vehicle CO concentrations in Mexico City were much higher than those reported for previous studies in the U.S.A.

EFFECT OF OZONE ON RADISH AND TURNIP UNDER EGYPTIAN FIELD CONDITIONS

EDU was used to assess the impact of ozone on the growth and yield of local varieties of radish (Raphanus sativus L.) and turnip (Brassica rapa L.) at two sites in northern Egypt. At a suburban site, in Alexandria, the growth of radish was significantly increased by application of the anti-ozonant N-[2-(2-oxo-l-imidazolidinyl) ethyl]-N′phenylurea (EDU) but turnip was unaffected. At a rural site, Abbis, 35 km south of Alexandria, the increase in growth of radish caused by EDU was higher than at Alexandria, and a significant increase in the growth of turnip was also found. These effects were consistent with the higher oxidant concentrations measured at Abbis compared with Alexandria. A controlled experiment involving ozone or filtered air treatments in open-top chambers demonstrated protective effects of ED U against ozone of a similar size found in the field, and that ED U had no significant effect on these species in the absence of ozone. This provides confidence that the effects of EDU in the field in Egypt can be ascribed to O3. The implications of the results for Egyptian agriculture are considered.

Growth and yield responses of Pakistan rice (Oryza sativa L.) cultivars to O3 and NO2

Abstract Two separate experiments were undertaken to determine Pakistan rice ( Oryza sativa L.) cultivar responses to air pollution, and specifically to test whether O 3 was the pollutant likely to have caused the large effects of filtration on rice yield found in earlier field experiments in Pakistan. In the first experiment (Exp 1), cv. IRRI-6 was exposed to ozone (O 3 ) at a mean concentration of 43 nl l −1 (8 h day −1 ) for 133 days until final harvest, covering both the vegetative and reproductive stages of growth. Results showed a significant reduction in total grain weight per plant. In the second experiment (Exp 2), fumigation of two rice cultivars with O 3 at 40−42 nl l −1 (8 h day −1 ) and nitrogen dioxide (NO 2 ) at 21–23 nl l −1 (24 h day −1 ), both singly and in combination, was carried out for 42 days during the vegetative stage of growth to determine if the presence of low concentrations of NO 2 might influence the responses of both cultivars to O 3 . Results showed O 3 to be more phytotoxic than NO 2 at the concentrations used. No significant O 3 ×NO 2 interactions were found at the time of harvest, but O 3 significantly reduced the photosynthetic capacity and biomass of both cultivars. Results of both experiments are compared with those reported for an open-top chamber filtration experiment carried out in Pakistan using the same two rice cultivars. Grain yield of cv. IRRI-6 was decreased in the closed chamber experiment by 57%, compared to a 37% decrease in the open-top chamber experiment; different yield components were affected in the open-top and closed chamber experiments which may be the result of differences in environmental conditions between the two studies. The results suggest that O 3 may have significant effects on rice yield in Pakistan and indicate that Pakistan rice cultivars have a high sensitivity to O 3 .

Effects of oxidants on soybean growth and yield in the Pakistan Punjab

Plants of soybean (Glycine max L.) were grown with and without the ozone protectant EDU (N-[2-(2-oxo-1-imidazolidinyl)ethyl]-n2 phenylurea) at a suburban site, a remote rural site and a rural roadside site around the city of Lahore, Pakistan. The development and yield of the plants was determined in two experiments--one immediately post-monsoon and one in the following spring (pre-monsoon). Concentrations of nitrogen dioxide and photochemical oxidants were measured at each site. The effect on yield of EDU at the suburban site (47 and 113% increase in seed weight per plant relative to the untreated plants in the post- and pre-monsoon experiments, respectively) was similar to the effects of filtration on yield on soybean in a parallel open-top chamber study at the same site (77% increase relative to plants subjected to unfiltered air for the pre-monsoon experiment). Effects of EDU on yield were greater at both rural sites than at the suburban site in both experiments, and greater in the spring experiment (182% at the remote rural site and 285% at the rural roadside site) than in the post-monsoon experiment (94% at the remote rural site and 170% at the rural roadside site); oxidant concentrations were also greater at the rural sites than at the suburban site, and greater in the spring experiment than the post-monsoon experiment. The results imply that ozone may be causing significant crop losses in rural areas around Lahore; however, the geographical extent of the problem, and the implications for peri-urban agriculture around other cities of south Asia are uncertain.

Modelling of indoor exposure to nitrogen dioxide in the UK

A dynamic multi-compartment computer model has been developed to describe the physical processes determining indoor pollutant concentrations as a function of outdoor concentrations, indoor emission rates and building characteristics. The model has been parameterised for typical UK homes and workplaces and linked to a time-activity model to calculate exposures for a representative homemaker, schoolchild and o

Effects of air pollution on the searching behaviour of an insect parasitoid

ce worker, with respect to NO 2 . The estimates of population exposures, for selected urban and rural sites, are expressed in terms of annual means and frequency of hours in which air quality standards are exceeded. The annual mean exposures are estimated to fall within the range of 5}21 ppb for homes with no source, and 21}27 ppb for homes with gas cooking, varying across sites and population groups. The contribution of outdoor exposure to annual mean NO 2 exposure varied from 5 to 24%, that of indoor penetration of outdoor air from 17 to 86% and that of gas cooking from 0 to 78%. The frequency of exposure to 1 h mean concentrations above 150 ppb was very low, except for people cooking with gas. ( 2000 Elsevier Science Ltd. All rights reserved.