Weekday/Weekend Ozone Differences: What Can We Learn from Them?

Abstract

A national analysis of weekday/weekend ozone (O₃) differences demonstrates significant variation across the country. Weekend 1-hr or 8-hr maximum O₃ varies from 15% lower than weekday levels to 30% higher. The weekend O₃ increases are primarily found in and around large coastal cities in California and large cities in the Midwest and Northeast Corridor. Both the average and the 95th percentile of the daily 1-hr and 8-hr maxima exhibit the same general pattern. Many sites that have elevated O₃ also have higher O₃ on weekends even though traffic and O₃ precursor levels are substantially reduced on weekends. Detailed studies of this phenomenon indicate that the primary cause of the higher O₃ on weekends is the reduction in oxides of nitrogen (NO_x) emissions on weekends in a volatile organic compound (VOC)-limited chemical regime. In contrast, the lower O₃ on weekends in other locations is probably a result of NO_x reductions in a NO_x-limited regime. The NO_x reduction explanation is supported by a wide range of ambient analyses and several photochemical modeling studies. Changes in the timing and location of emissions and meteorological factors play smaller roles in weekend O₃ behavior. Weekday/weekend temperature differences do not explain the weekend effect but may modify it.     

Antioxidants in Capsicum chinense: Variation among countries of origin

The main objective of this investigation was to evaluate fruits of C. chinense accessions for their concentration of β -carotene, ascorbic acid, and phenols for use as parents in breeding for these phytochemicals. Mature fruits of 63 accessions of C. chinense originally acquired from Belize, Brazil, Colombia, Ecuador, Mexico, Peru, Puerto Rico, and the United States were analyzed for their chemical composition. Fruits of C. chinense accessions PI-152452 (Brazil) and PI-360726 (Ecuador) contained the greatest concentrations of ascorbic acid (1.2 and 1.1 mg g^?1 fresh fruit, respectively), while PI-438648 (Mexico) contained the greatest concentration of total phenols content (349 μ g g^?1 fresh fruit) among the other 63 accessions tested. Accession PI-355817 from Ecuador contained the greatest concentrations of β -carotene (8 mg g^?1fresh fruit). These accessions were identified as potential candidates for mass production of antioxidants with health-promoting properties.     

Screening Capsicum chinense fruits for heavy metals bioaccumulation

Elevated concentrations of heavy metals in edible plants could expose consumers to excessive levels of potentially hazardous chemicals. Sixty-three accessions (genotypes) of Capsicum chinense Jacq, collected from 8 countries of origin were grown in a silty-loam soil under field conditions. At maturity, fruits were collected and analyzed for seven heavy metals (Cd, Cr, Ni, Pb, Zn, Cu, and Mo) concentrations. The main objectives of this investigation were: 1) to determine the concentrations of seven heavy metals in the soil and monitor their accumulation in mature fruits, 2) to categorize the pepper accessions as low or high heavy metal accumulators, and 3) to determine if heavy metal content of the pepper fruit was lower than the permitted limits. Concentrations and relative proportions of heavy metals in pepper fruits of C. chinense varied among accessions. Fruits of Plant Introduction (PI) 355820 accumulated significant concentrations of Cd (0.47 μ g g^?1dry fruit). PI-260522 accumulated the highest concentration of Pb (2.12 μ g g^?1 dry fruit) among the 63 accessions tested. This accession (PI-260522) contained about twice the Pb limit on a fresh weight basis. Among the 63 accessions analyzed, PI-238051 contained the highest levels of Ni (17.2 μ g g^?1). We concluded that high accumulator genotypes may be useful for phytoremediation, while, low accumulator accessions might be appropriate selections for growing on Cd-, Pb-, or Ni-contaminated soils to prevent potential human exposure to heavy metals and health hazards through the food chain.     

Chicken manure enhanced yield and quality of field-grown kale and collard greens

Organic matter and nutrients in municipal sewage sludge (SS) and chicken manure (CM) could be recycled and used for land farming to enhance fertility and physical properties of soils. Three soil management practices were used at Kentucky State University Research Farm, Franklin County, to study the impact of soil amendments on kale (Brassica oleracea cv. Winterbar) and collard (Brassica oleracea cv. Top Bunch) yields and quality. The three soil management practices were: (i) SS mixed with native soil at 15 t acre^?1, (ii) CM mixed with native soil at 15 t acre^?1, and (iii) no-mulch (NM) native soil for comparison purposes. At harvest, collard and kale green plants were graded according to USDA standards. Plants grown in CM and SS amended soil produced the greatest number of U.S. No. 1 grade of collard and kale greens compared to NM native soil. Across all treatments, concentrations of ascorbic acid and phenols were generally greater in kale than in collards. Overall, CM and SS enhanced total phenols and ascorbic acid contents of kale and collard compared to NM native soil. We investigated the chemical and physical properties of each of the three soil treatments that might explain variability among treatments and the impact of soil amendments on yield, phenols, and ascorbic acid contents of kale and collard green grown under this practice.     

Wild tomato leaf extracts for spider mite and cowpea aphid control

Glandular trichomes on the leaves of wild tomato, L. hirsutum f. hirsutum Mull, also known as Solanum habrochaites (Solanaceae), synthesize and accumulate high levels of methyl ketones (MKs). L. hirsutum accession LA 407, having high concentration of MKs, was grown from seeds under greenhouse conditions. Four MKs (2-undecanone, 2-dodecanone, 2-tridecanone, and 2-pentadecanone) were screened for their toxicity to spider mites, Tetranychus urticae Koch and cowpea aphids, Aphis craccivora Koch. The objectives of this investigation were to: (1) develop a bioassay for testing MKs on spider mite and cowpea aphid mortality and (2) compare the efficacies of wild tomato leaf crude extracts and pure standard materials of MKs against spider mite and cowpea aphid mortality. Our results revealed that spider mites are most sensitive to 2-tridecanone (LC₅₀ = 0.08 μmole cm^?2 of treated leaf surface) and least sensitive to 2-undecanone (LC₅₀ = 1.5 μmole cm^?2 of treated leaf surface) 4 h after treatment. Similarly, 2-tridecanone caused greatest mortality (LC₅₀ = 0.2 μmole cm^?2 of treated leaf surface), whereas 2-undecanone caused the lowest morality (LC₅₀ = 0.48 μmole cm^?2 of treated surface) of cowpea aphid. We concluded that all MKs tested in this investigation are toxic to spider mites and aphids. 2-Tridecanone is more effective in killing mites and aphids compared to other MKs. Toxicity of crude extracts, prepared from the leaves of L. hirsutum accession LA 407, to spider mites and cowpea aphids revealed greater mortality compared to a combined mixture of MKs standard material (used at the same concentration as found on LA 407 leaves). This indicates that in addition to MKs, other unidentified compounds in LA 407 leaf extract also have pesticidal properties. Accordingly, leaf extracts of LA 407 could be explored in crop protection, and they might open a new area of MK formulations and discovery of biorational alternatives for pest control in agricultural fields.     

1987 Joint EPRI/EPA Symposium on Stationary Combustion NOX Control

From March 23rd to 26th, 1987, the city of New Orleans hosted 350 attendees, including representatives from 15 foreign countries, at the 1987 Joint Symposium on Stationary Combustion NO_x Control. Cosponsored by the Electric Power Research Institute (EPRI) and the U.S. Environmental Protection Agency (EPA), the symposium provided attendees the opportunity to hear 49 papers in nine sessions covering technological and regulatory developments on NO_x control in the United States and abroad since the May 1985 symposium in Boston. Session topics included general environmental issues, low-NO_x combustion equipment (i.e., low-NO_x burners, reburning, etc.), flue gas treatment, fundamental combustion research, and special issues for cyclone coal-fueled boilers, oil- and gas-fired boilers, and industrial combustion applications.

Advances to the state-of-the-art presented at this symposium include: improved and/or newly applied combustion modifications for pulverized coal-fired boilers; further analyses of reburning, the leading combustion modification option for cyclone-equipped boilers; initial experiences with catalytic flue gas treatment in Europe; studies of NO_x control retrofit options for oil- and gas-fired utility systems; and new technology developments for coal, oil, and gas fueled utility and industrial combustors.

This paper summarizes those presentations that discussed significant changes since May 1985 in areas of potential interest to EPRI and its utility members. Where appropriate, they include our perspectives on the applicability of these newly disclosed findings to utility systems.     

Solvent Extraction Processes: A Survey of Systems in the SITE Program

Solvent extraction of contaminated soils, sludges and sediments has been successfully completed at a number of Superfund sites. Each commercialized process uses a unique operating system to extract organic contaminants from solids. These operating systems may be classified by the properties of the solvents each utilizes: (1) standard solvents, (2) near-critical fluids/liquified gases, and (3) critical solution temperature solvents. Pretreatment and post-treatment requirements vary depending upon the operating systems of the solvent extraction system. Future demonstrations of these technologies by the U.S. EPA’s Superfund Innovative Technology Evaluation Program will provide additional information regarding the efficacy of these processes.     

Ozone Control Strategies Based on the Ratio of Volatile Organic Compounds to Nitrogen Oxides

The 1990 Clean Air Act Amendments require states with O₃ nonattainment areas to adopt regulations to enforce reasonable available control technologies (RACT) for NO_X stationary sources by November 1992. However, if the states can demonstrate that such measures will have an adverse effect on air quality, NO_X requirements may be waived. To assist the states in making this decision, the U.S. EPA is attempting to develop guidelines for the states to use in deciding whether NO_X reductions will have a positive or negative impact on O3 air quality. Although NO_X is a precursor of O₃, at low VOC/NO_X ratios, the reduction of NO_X can result in increased peak O₃. EPA is examining existing information on VOC/NO_X ratios to develop “rules of thumb” to guide the states in their decision-making process. An examination of 6 a.m. to 9 a.m. VOC/NO_X ratios at a number of sites in the eastern U.S. indicates that the ratio is highly variable from day-to-day and there is no apparent relationship between ratios measured at different sites within the same area. In addition, statistical analysis failed to identify significant relationships between the 6 a.m. to 9 a.m. VOC/NO_X ratio and the maximum 1-hr. O₃ within a given area. Since we know from smog chamber and modeling studies that such a relationship exists, this further invalidates the assumption that a ratio measured at a single site is representative of the ratio for the entire region. Based on this Information, we conclude that having the 6 a.m. to 9 a.m. ambient VOC/NO_X ratio for a given area is insufficient information, by itself, to decide whether a VOC-alone, a NO_x-alone, or a combined VOC-NO_X reduction strategy is a viable or optimum O₃-reduction strategy.     

Controlled Enrichment System for Experimental Fumigation of Plants in the Field with Sulfur Dioxide

A prototype Free-Air Controlled Enrichment (FACE) system was developed at Brookhaven National "Laboratory (BNL) for the experimental control of gas concentrations in an open field, without any form of enclosure. This FACE system consists of a toroidal plenum chamber, 15 m in diameter, with a series of 32 vertical vent pipes from which the release of a test gas can be controlled. Data on gas concentration at the center of the array and wind velocity are fed to a microprocessor where a proportional, integrative, differential (PID) algorithm is used to regulate a mass-flow controller. Data on wind direction are used to control the opening and closing of the vertical vent pipes to maintain an upwind release. In 72 hours of continuous operation during which wind velocity varied between 0.3 to 8 m sec^-1, the FACE prototype maintained 1 -min averaged concentrations within twenty percent of the 40 ppb set point 94 percent of the time.