Assessing Impacts of Ozone on Agricultural Crops: I Overview

Abstract

The Environmental Protection Agency initiated the National Crop Loss Assessment Network (NCLAN) to develop pollutant dose-plant response information for economically important crop species. The primary thrust of the NCLAN program is to assess the effects of O₃ on crop yield. This paper is part of the third assessment report from NCLAN, which is composed of several cooperating programs with field sites in different regions of the country. Plants are grown in the field using open-top chambers for the control and manipulation of gas concentration around the crop plants. Four to six O₃ treatments are used in each experimental design and O₃ is added for 7 h/day in constant or proportional amounts to ambient air O₃ concentrations. The most extensive ambient O₃ monitoring data in the U.S. are provided by the Storage and Retrieval of Aerometic Data (SAROAD) system. By the use of an interpolative process called Kriging, county level O₃ concentrations can be estimated. Ozone concentrations are monitored in the NCLAN treatment chambers using shared-time monitoring. Data are summarized and presented as a seasonal mean of the daily 7-h mean O₃ concentrations for each treatment. The NCLAN air quality data are compatible with the SAROAD system. The NCLAN uses 0.025 ppm as an estimate of natural O₃ for comparison with the O₃ treatment concentrations. This value is also approximately equal to the O₃ concentrations in the charcoal filtered air (CF) chambers. In this report, four O₃ averaging times (exposure statistics) are compared for possible use in O₃ dose-crop yield models. Two seasonal mean exposure statistics (1-h and 7-h/day) and two peak exposure statistics (maximum 1-h and maximum 7-h/day mean) were compared by looking at the variation in the ratios of the seasonal 1-h/day mean and the two peak exposure statistics to the seasonal 7-h/day mean for the different treatments in each data set. The seasonal mean ratio (1-h/7-h) across O₃ treatments are more uniform than are the ratios of the peak statistics to the seasonal 7-h mean (peak 1-h/seasonal 7-h; peak 7-h/seasonal 7-h). The mean statistics are also less variable. A national assessment of crop yield loss from O₃ includes the integration of agricultural crop yield and acreage figures on a county basis, the spatial interpolation of SAROAD O₃ monitoring data to the county level, and the development of crop loss models that are specific for species or cultivars.