Howard E. Heggestad

Ethylene: An Urban Air Pollutant

Ethylene is an unusual air pollutant in that it is a plant hormone. Motor vehicle exhaust is a primary source. In the Washington, D. C, area, ethylene concentrations ranged from 700 ppb in the city center to 39 ppb in areas outside the circumferential beltway. Plants grown in these concentrations of ethylene, using controlled environment chambers, exhibited typical symptoms of ethylene toxicity: reduced growth, premature senescence, and reduced flowering and fruit production. When plants were grown in carbon-filtered ambient air, which was also filtered through KMnO4 to remove ethylene by oxidation, growth, flowering, and fruit production increased. These observations demonstrate that ethylene air pollution is a continual source of stress for plant growth and development in an urban environment.

Factors Influencing Ozone Dose—Yield Response Relationships in Open-top Field Chamber Studies

The National Crop Loss Assessment Network (NCLAN) consisted of a group of government and non-government organizations cooperating to determine immediate and potential effects of air pollution on crop production (Heck et al. 1982b, 1983b, 1984b). The major NCLAN objective was to obtain valid relationships between seasonal exposure to different levels of ozone (O3) and yields of important agricultural crops. Prior to NCLAN, results for only five field experiments of this type were available. The NCLAN program produced significant O3 dose-yield relationships from 38 field experiments. These dose-response results were needed for estimates of the annual impact on the US economy caused by a range of ambient O3 levels. These estimates are needed by the US EPA in setting national ambient air quality standards for O3.

The effects of photochemical oxidants on the yield of snap beans

Abstract Effects of photochemical oxidants (primarily ozone) in the ambient air of Eastern United States on the yields of selected snap bean ( Phaseolus vulgaris L.) cultivars grown from the seedling stage to maturity in “open-top” field chambers were studied. The chambers were supplied with either carbon-filtered or nonfiltered air. The research was conducted at Beltsville, Maryland, near Washington, D.C. during 1972–1976 and at Raleigh, North Carolina, in 1972. Cultivars Bush Blue Lake (BBL) 290, BBL 274 and Gallatin 50 represented processing type beans and Astro, fresh market beans. Two crops, an early and a late crop, were grown each year. At Beltsville from 1972 to 1974, BBL 290, the most sensitive cultivar to oxidants, averaged 14% less bean yield (range 5–27%) in nonfiltered air than in filtered air. Gallatin 50 and Astro, two oxidant tolerant cultivars, yielded about the same in the two environments. The results were similar in North Carolina. In 1975 yields were greatly reduced due to heavy rains. Consequently, no measurable yield effects attributable to oxidants could be determined. In the late crop in 1976, however, BBL 274 yielded 22% less in the nonfiltered air. The other three cultivars did not exhibit statistically significant oxidant induced yield losses. Yields in ambient air field plots without chambers were essentially equivalent to those in the nonfiltered chambers indicating that chamber effects per se were minimal. The microclimates of the chambers are described in an Appendix.

Photochemical oxidants potentiate yield losses in snap beans attributable to sulfur dioxide.

Field-grown snap beans (Phaseolus vulgaris) were given recurring midday exposures to sulfur dioxide in open-top field chambers containing ambient photochemical oxidants. There was a linear correlation (correlation coefficient = –.99) between increasing concentrations of sulfur dioxide and the yields of snap beans. Synergism was indicated for the mixtures of ambient ozone plus sulfur dioxide, leading to threefold greater yield losses in nonfiltered air than in charcoal-filtered air (to remove the ozone). Even the lowest sulfur dioxide dose in nonfiltered air reduced the yields of Astro, a cultivar that exhibited no visible pollutant-induced foliar injury.

Reduction in soybean seed yields by ozone air pollution

The National Crop Loss Assessment Network (NCLAN) determined that soybeans were more sensitive to ozone than other major agricultural crops, including corn, wheat, and cotton. The estimated production losses for soybeans at ambient levels of ozone ranged from 7.9 to 18.6 percent compared to 0.6 to 3.1 percent for corn. The research on soybeans was conducted in Illinois, North Carolina, Maryland, and New York. The loss estimates were obtained from field experiments using open-top chambers with charcoal-filtered (CF) air, nonfiltered (NF) air, and NF air with the addition of two or more increments of ozone. However, New Jersey scientists in two recent reports question the validity of the NCLAN results since the utilization of a different method to assess the impact of exposure of ambient O/sub 3/ on soybeans failed to show significant yield losses.

Air Pollution Research Needs: Herbaceous and Ornamental Plants and Agriculturally Generated Pollutants

Effects of various air pollutants on economically important crops and ornamentals have been studied since before the turn of the century. Summaries of this research on the effects of air pollutants, that have appeared in criteria documents developed by the Environmental Protection Agency, should be reviewed with respect to differences in plant susceptibility found in various regions of the country. These susceptibility differences are associated with variations in both environmental conditions and distribution of pollutants. Research efforts on air pollution injury to vegetation have often been poorly coordinated leaving many gaps in our knowledge. A better assessment of the impact of air pollution on vegetation is required to attain realistic controls for pollutants affecting agriculture. Research areas of major concern include: baseline information on effects of pollutants on agricultural productivity; dose-response information to support predictive mathematical models for acute and chronic studies of g...

Occurrence of high ozone concentrations in the air near metropolitan Washington

Relatively high concentrations of surface ozone and the indication that ozone is the inciting agent in fleck injury to tobacco were reported previously (1). Considerable interest therefore attaches to weather parameters on the high-ozone days which may throw light on the source and on the physicochemical processes affecting the ozone level. A source in the direction of nearby Washington, D.C., and photochemical production of the oxidant are indicated. Days with appropriate wind direction but low peak ozone concentration are discussed in terms of coexisting weather parameters. The weather ensemble found on highozone days is considered in relation to instances of fleck injury for which peak ozone levels were not measured.

Consideration of Air Quality Standards for Vegetation With Respect to Ozone

Present evidence suggests that ozone is the most damaging of all air pollutants affecting vegetation. It is the principal oxidant in the photochemical smog complex. Concentrations of ozone have exceeded 0.5 part per million (ppm) in the Los Angeles area. One-tenth of this level for 8 hours is known to injure very sensitive tobacco varieties. Many plant species are visibly affected after a few hours exposure at concentrations much lower than 0.5 ppm. There is also some evidence that ozone reduces plant growth. Many factors must be taken into account when considering standards to protect vegetation from ozone damage. These include ozone concentration and methods of measurement, time of exposure, possible additive effects of other pollutants, sensitivity of plant species, their economic value, and the extent of injury which can be tolerated. The response of a species to the pollutant is conditioned by genetic factors and environmental conditions. Lack of specific routine methods for measuring ozone in ambien...

Inhibition of photosynthesis and leaf conductance interactions induced by SO2, NO2, and SO2 + NO2.

Abstract Effects of 2-h exposures to 0–1 μmol mol −1 SO 2 , NO 2 and (1:1) SO 2 + NO 2 on CO 2 uptake by standardized snap bean leaves were studied. Interactions resulting from pollutant-induced changes in leaf conductance were evaluated. Minimum exposure concentrations required to depress CO 2 exchange rates (CER) under the test conditions were:0.17 μmol mol −1 SO 2 , 0.38 μmol mol −1 NO 2 , and 0.08 μmol mol −1 of each pollutant in the 1:1 mixture. Treatments with 1 μmol mol −1 NO 2 reduced CER 10% without affecting leaf conductance. One μmol mol −1 SO 2 depressed CER by 50%. Leaf conductances increased in SO 2 -treated leaves showing 30% inhibition of CER. Greater inhibition led to subsequent stomatal closure. Inhibition caused by the individual pollutants (applied singly) was linear over the range of concentrations investigated. The dual-pollutant mixture produced a synergistic response that was most pronounced at the lower pollutant concentrations. The potentiated effect was correlated with marked stomatal closure. Experimental plants for this study were grown under low moisture stress conditions to enhance stomatal opening in the plant stock material and reduce (damp) the potential for further SO 2 -induced stimulation of stomatal opening. The experiments were designed to obtain limiting data for the test conditions.