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Vol. 9 No. 2 - April 2003

Air Pollution Impacts on Crops and Forests

in Developing Countries

By: L.D. Emberson1, M. Agrawal2, A. Wahid3, M.R. Ashmore4, H. Pleijel5, P.E.Karlsson6

Increases in air pollution over recent decades have been experienced in many industrial and urban centres of Asia, Africa and Latin America primarily as a result of rapid economic growth which has led to industrialization, urbanization, increases in motor vehicle use and associated increases in energy demands. To date, relatively little is known about pollutant concentrations and exposure patterns in most suburban and rural areas and associated impacts on the local vegetation of developing countries.

The earlier phase of this RAPIDC project commissioned experts from a number of developing countries to collate evidence describing local / regional emissions, vegetation distributions and associated local pollutant concentrations. This information was related to observations of visible injury in the field and key experimental investigations describing the direct effects of a number of different air pollutants on selected crop and forest species. The information collated during the initial phase of this project has clearly shown that in many developing country regions, and particularly in parts of Asia, crop yields and forest productivity are being severely affected by local ambient air pollutant concentrations.

One of the main aims of Phase I of the project was to assess the transferability of pollutant damage assessment methods developed in Europe and North America to developing country situations. The definition of dose-response relationships or exposure limits for damage is one component of achieving such an aim. Preliminary attempts to investigate the potential regional differences in dose-response relationships have been made by pooling suitable data collected for sulphur dioxide from exposure studies conducted in China, India, Europe and Australia. It is evident that large differences exist in sensitivity to equivalent sulphur dioxide concentrations. However, the data suggest that the species with higher sensitivities are consistent across regions, for example both the Indian and Chinese studies identified beans as an especially sensitive genus. The range of species response to increasing exposures seems broadly consistent between regions indicating a degree of commonality.

Similar dose-response data have been pooled for forest tree species allowing the comparison of responses to varying ozone exposures of Japanese deciduous and coniferous tree species with equivalent European species. Further, there is considerable variability in the response of different Japanese tree species to ozone exposure. Comparison with European beech (a sensitive European species) suggests that the most sensitive species in Japan have similar responses to ozone exposure as the most sensitive European species. Similar results are found on comparison of the Japanese and European coniferous species. Overall, these data suggest a broad consistency in exposure-response relationships for sensitive species of both trees and agricultural crops from different regions. However, much more work is needed to define robust dose-response relationships that would be appropriate for use in studies to assess the socioeconomic impacts of pollution damage to vegetation. It is the identification of appropriate methods to establish such relationships that will form a significant part of this second phase of the project.

The Regional Air Pollution in Developing Countries (RAPIDC) programme aims to facilitate the development of agreements/protocols and to implement measures which prevent and control air pollution through promoting international co-operation and developing scientific information for the policy process. The RAPIDC programme is co-ordinated by the Stockholm Environment Institute (SEI) and funded by Sida (the Swedish International Development Co-operation Agency). The "Air Pollution: Crops and Forests" project is a component of the RAPIDC programme which focuses on assessing damage to agricultural crops and forest productivity caused by ambient pollution levels in developing country regions, with a particular focus on the Asian region. Further details concerning the overall RAPIDC programme can be found at www.rapidc.org

To ensure that appropriate data are collected in Phase II of this project it is important to consider how these data would be used to inform the implementation of emission reduction policy initiatives. There is a real need to provide some indication of the potential risk to which agricultural crops and forest trees are exposed under current-day air pollution concentrations, and the increased risk which may arise from future predicted increases in emissions. Exposure-response relationships can be used to assess the change in the degree or risk of damage for a given change in pollutant exposure. This requires the integration of various datasets including regionally mapped pollutant concentration data and receptor information to show species location. These data can be overlaid to produce maps capable of highlighting cooccurrence of sensitive vegetation types and potentially damaging pollutant concentrations and hence where there may be a risk of crop yield reductions and damage to the health and productivity of forests. This information may then be used in socio-economic impact analyses or cost-benefit analyses that estimate the environmental benefits of investment in measures to reduce pollutant emissions.

The data necessary to define pollutant impacts on vegetation need to be collected under careful consideration of the local and regional factors that will no doubt affect vegetation response to air pollution. For example, are all factors known to alter plant sensitivity to air pollution and as such will need to be taken into account when establishing any kind of observational or experimental protocol to collect exposure-response information.

It may be possible to use the following options to collect the information necessary to relate pollutant exposure to damage. It is possible to define two separate aims and uses for these data: i) to define dose-response relationships or an appropriate equivalent that can be used to perform socioeconomic pollutant impact assessments, and ii) to help validate local and regional assessments of damage produced through the application dose-response relationships.


  • Systematic records of visible injury observed on specific crop and forest species across regions.


  • Bio-monitoring using well documented indicator plants.

  • Transect studies investigating the variability of damage to vegetation along air pollution gradients.

  • Studies using chemical protectants.

  • Experimental studies (e.g. open-top chamber filtration studies, open release systems etc..).

  • Epidemiological studies investigating statistical relationships between specific damage parameters and air pollution exposure.

  • Methods to assess risk of damage by pollutant concentrations

  • Preliminary semi-quantitative identification of possible risk areas on consideration of pollutant concentrations, climatic conditions and location of known sensitive species.

  • Quantitative estimates of socioeconomic impacts of pollutants. These would require the establishment of robust speciesspecific relationships relating exposure indices to damage.

The second phase of the project will concentrate on identifying which of the above methods will be suitable for application across the Asian region. Many factors will need to be considered when trying to select appropriate methods for developing country situations. Some of the more important will no doubt relate to: i) the suitability of the experimental methods to developing country conditions; ii) the ability of the methods to provide information on the response of vegetation relevant to appropriate, social and economic conditions (e.g. yield and nutritional status of crops); and iii) the financial and logistical constraints to establishing and conducting observational or experimental procedures.


  • Establish a network of air pollution effects scientists with emphasis on South Asia, but including practitioners in the rest of Asia.

  • Use of questionnaire surveys to identify major knowledge gaps and the potential for developing a common manual describing methods for assessing crop-yield reductions and loss in forest productivity under Asian conditions.

  • Develop an experimental protocol for Asian and other developing country conditions to enable socioeconomic risk assessments to be performed.

  • Produce a background document, summarising the current status of knowledge of pollutant impacts on vegetation in the Asian region.

  • Hold a workshop for the Air Pollution Network in South Asia to assess the current state of knowledge of air pollution impacts, discuss and agree the proposed manual/protocol, and bring together regional air pollution experts, decision-makers and other appropriate stakeholders. Key topics for discussion at the workshop will be the transferability of European/North American experience and air quality management tools (including critical levels, dose-response relationships and air quality guidelines) to the Asian region.

1Stockholm Environment Institute at York, Biology Dept., University of York, York, U.K.

2Dept. of Botany, Banaras Hindu University, Varanasi, India.

3Environmental Pollution Research Laboratory, Botany Department, Government College Lahore, Pakistan.

4Dept. of Environmental Science, University of Bradford, Bradford, U.K.

5Goteborgs Universitet, Goteborg, Sweden

6IVL, Swedish Environmental Research Institute, Goteborg, Sweden

This article has been reproduced from the archives of EnviroNews - Newsletter of ISEB India.

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