Roger L. Tanner

Characterization and Quantification of Isoprene-Derived Epoxydiols in Ambient Aerosol in the Southeastern United States

Isoprene-derived epoxydiols (IEPOX) are identified in ambient aerosol samples for the first time, together with other previously identified isoprene tracers (i.e., 2-methyltetrols, 2-methylglyceric acid, C(5)-alkenetriols, and organosulfate derivatives of 2-methyltetrols). Fine ambient aerosol collected in downtown Atlanta, GA and rural Yorkville, GA during the 2008 August Mini-Intensive Gas and Aerosol Study (AMIGAS) was analyzed using both gas chromatography/quadrupole mass spectrometry (GC/MS) and gas chromatography/time-of-flight mass spectrometry (GC/TOFMS) with prior trimethylsilylation. Mass concentrations of IEPOX ranged from approximately 1 to 24 ng m(-3) in the aerosol collected from the two sites. Detection of particle-phase IEPOX in the AMIGAS samples supports recent laboratory results that gas-phase IEPOX produced from the photooxidation of isoprene under low-NO(x) conditions is a key precursor of ambient isoprene secondary organic aerosol (SOA) formation. On average, the sum of the mass concentrations of IEPOX and the measured isoprene SOA tracers accounted for about 3% of the organic carbon, demonstrating the significance of isoprene oxidation to the formation of ambient aerosol in this region.

Intercomparison of near real time monitors of PM2.5 nitrate and sulfate at the U.S. Environmental Protection Agency Atlanta Supersite

[1] Five new instruments for semicontinuous measurements of fine particle (PM2.5) nitrate and sulfate were deployed in the Atlanta Supersite Experiment during an intensive study in August 1999. The instruments measured bulk aerosol chemical composition at rates ranging from every 5 min to once per hour. The techniques included a filter sampling system with automated water extraction and online ion chromatographic (IC) analysis, two systems that directly collected particles into water for IC analysis, and two techniques that converted aerosol nitrate or sulfate either catalytically or by flash vaporization to gaseous products that were measured with gas analyzers. During the one-month study, 15-min integrated nitrate concentrations were low, ranging from about 0.1 to 3.5 μg m -3 with a mean value of 0.5 μg m -3 . Ten-minute integrated sulfate concentrations varied between 0.3 and 40 μg m -3 with a mean of 14 μg m -3 . By the end of the one-month study most instruments were in close agreement, with r-squared values between instrument pairs typically ranging from 0.7 to 0.94. Based on comparison between individual semicontinuous devices and 24-hour integrated filter measurements, most instruments were within 20-30% for nitrate (∼0.1-0.2 μg m -3 ) and 10-15% for sulfate (1-2 leg m -3 ). Within 95% confidence intervals, linear regression fits suggest that no biases existed between the semicontinuous techniques and the 24-hour integrated filter measurements of nitrate and sulfate;, however, for nitrate, the semicontinuous intercomparisons showed significantly less variability than intercomparisons amongst the 24-hour integrated filters.

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.

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.

Assessment of Nontailpipe Hydrocarbon Emissions from Motor Vehicles

This report evaluates tailpipe and nontailpipe hydrocarbon (HC) emissions from light-duty spark-ignition (SI) vehicles. The sources of information were unpublished data sets, generated mainly from 1990 through 1994, on emissions from volunteer fleets of in-use vehicles in chassis dynamometer and sealed housing for evaporative determination tests, and published chemical mass balance (CMB) source apportionments of HC in roadway tunnels and in urban air. The nontailpipe emissions evaluated comprise running-loss, hot soak, diurnal emissions, and resting-loss emissions. Relations between pressure and purge test failures and actual nontailpipe emissions were also examined.

Influence of natural hydrocarbons on ozone formation in an isolated power plant plume

On 4 days during the 1995 Southern Oxidant Study (SOS), air samples were taken in the plume of the Cumberland Power Plant in Tennessee using an instrumented helicopter. On these days a notable difference in excess ozone in the plumes was observed. Excess ozone varied from 20 ppb on July 7, 1995, up to 55 ppb on July 16. While the total amount of non-methane VOC was quite similar, significant differences were observed in the levels of reactive hydrocarbons, mostly isoprene. This study examines the parameters that govern both emission rates of isoprene and its dispersion. These include temperature and wind speed on the surface and aloft, total solar radiation, and the height of the mixed layer. The results revealed and computer model simulations confirmed that although differences were not very large, the combinations of all of these parameters favored lower ambient isoprene levels and, consequently, lower ozone production on July 7 and higher production on the 3 other days.

Measurement of total nonmethane organic carbon (Cy): Development and application at Chebogue Point, Nova Scotia, during the 1993 North Atlantic Regional Experiment campaign

A technique was developed for the measurement of total nonmethane organic carbon (Cy) in the gas phase based on cryogenic collection, preseparation of CO, CH4 and CO2, conversion of all carbon to CH4, and measurement by flame ionization detector. Collection and recovery efficiencies were found to be essentially quantitative for C2-C7 hydrocarbons and better than 95 and 93% for methanol and formaldehyde, respectively. CO2 prevented the measurement of the C2 hydrocarbons in atmospheric samples, and system response to ambient water vapor limited the precision of the measurement at very low Cy. The measurement system had an estimated uncertainty of 10% at ambient mixing ratios of 100 ppb C, and a detection limit of between 5 and 7 ppb C. Cy was measured in Boulder, Colorado, during June of 1993 and at Chebogue Point, Nova Scotia, during the North Atlantic Regional Experiment intensive campaign, August to September 1993. Cy values ranged from several hundred ppb C to 11 ppb C in Boulder, and from 177 to below 5 ppb C at Chebogue Point, with medians of 55 and 11 ppb C, respectively. Cy was found to correlate with both CO and O3 at higher levels of those two pollutants. The sum of Cy and the C2 hydrocarbons was virtually always equal to or greater than the sum of the hydrocarbons. Several exceptions to this occurred when high HC values were observed in cannister samples but not Cy measurements. These instances were attributed to short-term perturbations from local sources. There was a net difference between total nonmethane organic carbon and the sum of hydrocarbons and carbonyls of 3.5±7.8 ppb C overall. This difference appears to be broadly correlated with anthropogenic pollution. There does not appear to be a significantly large reservoir of reactive carbon unaccounted for by hydrocarbon or carbonyl measurements.

Loss rate of NO y from a power plant plume based on aircraft measurements

This study was motivated by the recent work of Buhr et al. [1996] which reported losses of NOy from large power plant plumes as high as 0.25 hour−1, much higher than generally accepted values. If true, conclusions pertaining to the efficiency of ozone and nitrate production in the lower troposphere would need major revisions. The results of Buhr et al. were based on aircraft measurements in four TVA (Tennessee Valley Authority) power plant plumes on July 7, 1995, as part of the Nashville/Middle Tennessee Ozone Study, a measurement program of the Southern Oxidants Study (SOS), whereas the results reported in this paper are also based on measurements made in the same SOS study aboard another instrumented aircraft (the TVA helicopter), in plumes of one of these power plants (the Cumberland Steam Plant in northwestern Tennessee) during five different days in 1994 and 1995. Between the 1994 and 1995 sampling periods, emissions of SO2 at the Cumberland plant were reduced by nearly 95% by installation of scrubbers. Our data from the one 1994 day show that the ratio of excess SO2 to NOy, in the plume core increased significantly with plume age, indicating a potentially high differential loss rate of NOy (excess loss of NOy relative to SO2) of about 0.12 hour−1. However, results based on the larger 1995 data set indicate a low differential NOy loss rate of only 0.00±0.03 hour−1, consistent with accepted low loss rates. Because the SOS-Nashville/Middle Tennessee Ozone Study was not specifically designed to explore the NOy loss issue, the question of NOy loss rates in plumes is not currently resolved and additional focused field studies are needed.

High-Volume Diffusion Denuder Sampler for the Routine Monitoring of Fine Particulate Matter: II. Field Evaluation of the PC-BOSS

The high-volume Brigham Young University organic sampling system with a particle concentrator (PC-BOSS) has been field evaluated for the determination of airborne fine particulate matter including semivolatile chemical species during 3 intensive sampling programs in 1997: Tennessee Valley Authority (TVA), Lawrence County, TN; Riverside, CA; and Provo, UT. The PC-BOSS precision was tested using 2 collocated PC-BOSS samplers. In addition, the PC-BOSS results were compared with results from a prototype PM 2.5 U.S. EPA federal reference method (FRM sampler), a filter pack sampler (quartz and charcoal sorbent filters), the BIG BOSS, an annular denuder sampler, and the ChemSpec sampler for the determination of major fine particulate species. Fine particulate mass, sulfate, nitrate, and organic carbonaceous material (OC) determined by 2 PC-BOSS samplers agreed within - 10%. Possibly due to absorption of SO 2 by a quartz filter, the sulfate concentrations determined by the filter pack sampler and the BIG BOSS were higher (by 10 - 3%) than concentrations obtained with the other samplers. No absorption of SO 2 (g) by the quartz filters of the PC-BOSS occurred due to the high efficiency (>99%) of its denuder. The PC-BOSS, annular denuder, and ChemSpec samplers agreed with each other (to within - 0.5 w g/m 3 , - 17%, with no bias) for the determination of fine particulate nitrate concentrations, including volatilization losses. The prototype PM 2.5 FRM sampler collected only particle-retained nonvolatile mass. The mass concentrations determined by the PM 2.5 FRM agreed with those collected by the post-denuder Teflon filters of the PC-BOSS (to within - 1.1 w g/m 3 , - 10%, with no bias). The overall loss of material from particles and the resultant underestimation of the particulate mass concentrations by the PM 2.5 FRM depended on the fine particle composition and the ambient temperature.