William J. Parkhurst

Rural ozone in the southeastern United States

Abstract Ozone measurements are reported for five rural sites in the Tennessee Valley region of the southeastern U.S. for periods ranging from 18 to 83 months during the years 1977 through 1984. Rural ozone (O 3 ) levels were found to equal or exceed urban values for the same region. The daily maximum 1-h average concentration was found to peak during the summer months, while the 24-h average concentrations were greatest in the spring. The annual cycle of daily maximum concentrations is related to the seasonal photochemical cycle. The annual cycle in 24-h average concentrations is best explained by the combined effects of the annual cycles in solar intensity and noctural O 3 depletion. There was no indication that stratospheric intrusions exhibited a significant influence on the annual O 3 cycles. Evidence was found for elevated O 3 levels during touchdown of plumes from large power plants. No long-term trend in rural O 3 concentrations, either daily maxima or means, was discernible.

Ozone formation and transport in southeastern United States: Overview of the SOS Nashville/Middle Tennessee Ozone Study

The Southern Oxidants Study (SOS) is a public-private partnership collectively engaged, since 1989, in a coordinated program of policy-relevant research to improve scientific and public understanding of tropospheric ozone pollution. In the summers of 1994 and 1995, SOS implemented the Nashville/Middle Tennessee Ozone Study. This effort, the second SOS urban intensive study, conducted a series of integrated, process-oriented airborne and surface measurement experiments to better understand the chemistry and meteorology associated with the production, transport, and impact of tropospheric ozone. Specific technical objectives addressed (1) the role of biogenic VOC and NOx emissions on local and regional ozone production, (2) the effect of urban-rural exchange/interchange on local and regional ozone production, (3) sub-grid-scale photochemical and meteorological processes, and (4) the provision of a high-quality chemical and meteorological data set to test and improve observation- and emission-based air quality forecast models. Some of the more significant findings of the 1994–1995 studies include the following: (1) Ozone production in Nashville was found to be close to the transition between NOx-sensitive and VOC-sensitive chemistry. (2) Ozone production efficiency (OPE) in power plant plumes, molecules of ozone formed per molecule of NOx emitted, was found to be inversely proportion to NOx emission rate, with the plants having the greatest NOx emissions exhibiting the lowest OPE. (3) During stagnant conditions, nighttime winds dominated pollutant transport and represent the major mechanism for transporting urban pollutants to rural areas. Ultimately, results provided by this research will allow improved assessment of existing ozone management strategies and provide better scientific tools for the development of future management strategies.

Fossil Sources of Ambient Aerosol Carbon Based on 14C Measurements Special Issue of Aerosol Science and Technology on Findings from the Fine Particulate Matter Supersites Program

Organic and elemental carbonaceous material constitute significant portions of PM10 and PM2.5 mass on a global basis and are typically 35% and 10%, respectively, in urban areas of the southeastern United States. The organic portion of this is a complex mixture of primary compounds and secondary materials formed in situ from primary emissions. These materials derive from a variety of sources that are dynamically changing in time and space, making difficult the quantitative characterization of their sources. Results of measurements of the 14C content of organic aerosol particles (PM10 and TSP) sampled at Look Rock, TN are reported in this work with the aim of better estimating bounds to fossil and biogenic sources that contribute to PM mass concentrations. The fraction of fossil-derived carbon in these particles has been estimated as 1 minus the fraction of “modern” carbon, the latter by definition biologically synthesized in equilibrium with atmospheric, cosmic ray-derived 14CO2. Fossil carbon fractions vary in a wide range from less than 10 to about 60% during spring, summer, and fall seasons at this ridge-top site near the Great Smoky Mountains National Park. The implications of these findings on control strategies for the organic carbon fraction of PM2.5 mass are discussed.

Outdoor/Indoor/Personal Ozone Exposures of Children in Nashville, Tennessee

Abstract An ozone (O3) exposure study was conducted in Nashville, TN, using passive O3 samplers to measure six weekly outdoor, indoor, and personal O3 exposure estimates for a group of 10- to 12-yr-old elementary school children. Thirty-six children from two Nashville area communities (Inglewood and Hendersonville) participated in the O3 sampling program, and 99 children provided additional time-activity information by telephone interview. By design, this study coincided with the 1994 Nashville/Middle Tennessee Ozone Study conducted by the Southern Oxidants Study, which provided enhanced continuous ambient O3 monitoring across the Nashville area. Passive sampling estimated weekly average outdoor O3 concentrations from 0.011 to 0.030 ppm in the urban Inglewood community and from 0.015 to 0.042 ppm in suburban Hendersonville. The maximum 1- and 8-hr ambient concentrations encountered at the Hendersonville continuous monitor exceeded the levels of the 1- and 8-hr metrics for the O3 National Ambient Air Quality Standard. Weekly average personal O3 exposures ranged from 0.0013 to 0.0064 ppm (7-31% of outdoor levels). Personal O3 exposures reflected the proportional amount of time spent in indoor and outdoor environments. Air-conditioned homes displayed very low indoor O3 concentrations, and homes using open windows and fans for ventilation displayed much higher concentrations.

Chiral pesticides as tracers of air–surface exchange

The enantiomers of chiral pesticides are selectively broken down in soil and water to yield residues and metabolites, which are non-racemic. The distinctive enantiomer signatures of residues are pr ...

Chemical Composition of Fine Particles in the Tennessee Valley Region

ABSTRACT Fine particles in the atmosphere have elicited new national ambient air quality standards (NAAQS) because of their potential role in health effects and visibility-reducing haze. Since April 1997, Tennessee Valley Authority (TVA) has measured fine particles (PM2.5) in the Tennessee Valley region using prototype Federal Reference Method (FRM) samplers, and results indicate that the new NAAQS annual standard will be difficult to meet in this region. The composition of many of these fine particle samples has been determined using analytical methods for elements, soluble ions, and organic and elemental carbon. The results indicate that about one-third of the measured mass is SO4 -2, one-third is organic aerosol, and the remainder is other materials. The fraction of SO4 -2 is highest at rural sites and during summer conditions, with greater proportions of organic aerosol in urban areas throughout the year. Additional measurements of fine particle mass and composition have been made to obtain the short-term variability of fine mass as it pertains to human exposure. Measurements to account for semi-volatile constituents of fine mass (nitrates, semi-volatile organics) indicate that the FRM may significantly under-measure organic constituents. The potentially controllable anthropogenic fraction of organic aerosols is still largely unknown.

Historic PM2.5/PM10 Concentrations in the Southeastern United States—Potential Implications of the Revised Particulate Matter Standard

This report summarizes a PM2.5/PM10 particulate matter data set consisting of 861 PM2.5/PM10 sample pairs collected with dichotomous samplers by the Tennessee Valley Authority (TVA) from 1982 to 1991. Eight monitoring stations, ranging from urban-industrial to rural-background, were operated across three east-central U.S. states. Annual average PM2.5 concentrations ranged from 12.6 to 21.3 micrograms per cubic meter (μg/m3), with an overall mean of 15.7 μg/m3. Likewise, annual average PM10 concentrations ranged from 17.8 to 33.7 μg/m3, with an overall mean of 23.7 μg/m3. High summer-low winter seasonality was evident, particularly for PM2.5, with the highest monthly PM2.5 and PM10 concentrations in August (26.4 and 37.5 μg/m3, respectively) and the lowest in February (9.9 and 15.3 μg/m3, respectively). A strong association (r2 = 0.84) was found between PM and PM mass with PM mass contributing, on average, 67% of PM10 mass. Applying TVAs PM2 5/PM10 ratio to recent (1993-1995) regional high-volume PM10 Aerometric Information Retrieval System (AIRS) data for the east-central United States suggests that as many as 80% of monitored counties would have equaled or exceeded the level of the new annual PM2.5 metric of 15 μg/m3. A decline in average PM2.5 mass on the order of 3-5 μg/m3 from 1982 through 1991 is also suggested. Daily PM2 5 mass appears to be reasonably well associated (r = 0.47) with maximum hourly ozone during the warmer months (spring through fall). Sulfate compounds comprise a major portion of the measured PM2 5 mass, with that fraction being highest in the summer months. Viewed collectively, these data suggest that although compliance with the annual and 24-hr PM and 24-hr PM metrics should prove readily attainable, the annual PM2.5 metric will present a major regulatory management challenge for much of the east-central United States.

Air chemistry during the 1995 SOS/Nashville intensive determined from level 2 network

Air quality measurements from enhanced ground-based air monitoring stations, that were located at strategic urban, suburban, and rural (regional) locations, were used to determine the factors controlling excess ozone formation in the Nashville area. During the 6 week intensive study period, the daily maximum hourly O3 concentrations varied from daytime highs of less than 40 ppbv to values exceeding 120 ppbv. The higher O3 concentrations were observed at the urban and suburban locations, and the highest O3 value of 138 ppbv was observed at the downtown Nashville station. On 12 days, one or more of the urban and suburban stations exceeded midday 8-hour mean O3 concentrations of 80 ppbv in contrast to the single occurrence at the rural stations. The observations that the elevated O3 concentrations occurred more frequently at the urban and suburban stations during stagnating weather conditions suggest localized production of excess O3. The comparison of the O3/NOy ratios to model simulations suggest that the rural and suburban locations are in a NOx sensitive chemistry regime, while the urban location (downtown Nashville) is in a chemistry regime that is sensitive to both NOx and VOC concentrations. The O3 production efficiency, determined from the slope of the O3 versus NOz (NOy - NOx), was found to be similar between the Dickson and Youth suburban stations and the Giles rural/regional station. The segregation of the data by SO2 concentration showed lower O3 production efficiency for those measurement periods with SO2 concentrations greater than 2 ppbv. The slopes (upper limits of O3 production efficiency) ranged from 7.7 to 10.6 for the lower SO2 concentrations and from 4.4 to 4.6 for the higher SO2 concentrations.

Impact of the 1998 Central American fires on PM2.5 mass and composition in the southeastern United States

Abstract The impact of the Central American fires on PM2.5 mass concentration and composition in the Tennessee Valley region during portions of May, 1998, has been quantified. Elevated concentrations of smoke aerosol tracers—fine potassium, (and to a lesser extent, calcium and silicon) and, where available, organic and elemental carbon—were observed in the region during times in which satellite imagery (TOMS and GOES-8) showed regional transport of hazy, smoky airmasses from southern Mexico and adjacent areas of Central America. Back-trajectories from network sites in the Tennessee Valley network were consistent with this regional transport. The extent of transport of extra-regional fine particle mass during May, 1998, is discussed relative to the new US fine particle mass-based standards for fine particulate matter.

Rates of Conversion of Sulfur Dioxide to Sulfate in a Scrubbed Power Plant Plume

ABSTRACT The rate of conversion of SO2 to SO4 2- was re-estimated from measurements made in the plume of the Cumberland power plant, located on the Cumberland River in north-central Tennessee, after installation of flue gas desulfurization (FGD) scrubbers for SO2 removal in 1994. The ratio of SO2 to NOy emissions into the plume has been reduced to ~0.1, compared with a prescrubber value of ~2. To determine whether the SO2 emissions reduction has correspondingly reduced plume-generated particulate SO4 2- production, we have compared the rates of conversion before and after scrubber installation. The prescrubber estimates were developed from measurements made during the Tennessee Plume Study conducted in the late 1970s. The post-scrubber estimates are based upon two series of research flights in the summers of 1998 and 1999. During two of these flights, the Cumberland plume did not mix with adjacent power plant plumes, enabling rate constants for conversion to be estimated from samples taken in the plume at three downwind distances. Dry deposition losses and the fact the fact that SO2 is no longer in large excess compared with SO4 2- have been taken into account, and an upper limit for the conversion rate constant was re-estimated based on plume excess aerosol volume. The estimated upper limit values are 0.069 hr-1 and 0.034 hr-1 for the 1998 and 1999 data, respectively. The 1999 rate is comparable with earlier values for nonscrubbed plumes, and although the 1998 upper limit value is higher than expected, these estimates do not provide strong evidence for deviation from a linear relationship between SO2 emissions and SO4 2- formation.