Characterization of Ozone During Consecutive Drought and Wet Years at a Rural West Virginia Site

Ozone concentrations at a rural-remote site in a forested region of north-central West Virginia were monitored during 1988 and 1989, a drought and wet year, respectively. During 1988, the absolute maximum average concentration for a single hour was 156 ppb, while it was only 107 ppb in 1989. Overall, the frequency of high concentrations was greater during 1988; the 120 ppb National Ambient Air Quality Standard was exceeded 17 times. The 7-h period encompassing the highest growing season concentrations for this site over the 2-yr period is 1100- 1759 h EST, rather than the period 0900-1559 h originally used by the National Crop Loss Assessment Network. The 7-h growing season means (0900-1559 h) of 52.6 ppb and 47.1 ppb for 1988 and 1989, respectively, compare well to those reported for the Piedmont/Mountain/Ridge-Valley area, but are higher than those for other surrounding areas. The diurnal ozone patterns, as well as the distribution of concentration ranges and timing of seasonal maxima, suggest that long-range transport of ozone and its precursors probably is an important factor at this site, given its remote and rural character.     

Indoor/Outdoor Measurements of Volatile Organic Compounds in the Kanawha Valley of West Virginia

The Kanawha Valley region of West Virginia which is comprised of Charleston and surrounding communities Is the center of a heavily industrialized area known for its chemical manufacturing. As part of a larger study designed to investigate the Impact of the chemical industry on human exposures to volatile organic compounds (VOC), a study of the relationship between indoor and outdoor concentrations was conducted. Thirty-five homes were selected for monitoring from among volunteers; approximately ten in each of three distinct population-industry centers and four outside the Valley to act as controls. Monitoring was performed using passive, badge samplers with a three-week monitoring period. Two separate questionnaires were administered: one for characterization of the residence; and one to characterize source use during monitoring. Participants were also asked to keep a record of their activities with respect to in-home, outdoors and other Indoor environments. Analysis of the samplers was performed by solvent extraction followed by gas chromatography using a flame-ionization detector. Results suggest that indoor VOC concentrations are higher than outdoor concentrations. Additionally, certain ventilation-related parameters were identified that afforded some predictive power for indoor concentrations. No statistically significant differences between regions were identified.     

Severity of SO2-lnduced Leaf Necrosis on Caribbean,Scots, and Virginia Pine Seedlings

Caribbean pine, an economically important tree of tropical lowlands, is at risk of SO₂ exposure in certain locales. Twenty-week old seedlings of Caribbean, Scots, and Virginia pine were exposed to 0.5, 1.0, and 2.0 ppm SO₂ (1300, 2600, and 5200 μm^?3, respectively) for 1, 2, 4, and 8 h in modified controlled-environment chambers. Severity of SO₂-induced leaf necrosis for each species was related to SO₂ concentration and exposure duration using a regression model. The three dose-response relationships differed in detail, but Caribbean pine seedlings were generally as sensitive to SO₂ as seedlings of the two highly sensitive temperate species. In addition, 173 4-wk-old Caribbean pine seedlings were exposed to 0.5 ppm SO₂ for 4 h. Over one-half of these seedlings exhibited some necrosis and over one-sixth had more than 5 percent of leaf surface necrotic. It is concluded that Caribbean pine seedlings are highly sensitive to acute doses of SO₂.     

Tagging Diesel and Residential Oil Furnace Emissions in Roanoke,Virginia, with Enriched Isotopes of Samarium

Stable isotopic tracers were used in Roanoke, Virginia, to tag particulate emissions from diesel trucks and residential oil furnaces, two sources of soot and PAHs which cannot be differentiated on the basis of known constituents. Approximately 1.6 g of enriched ¹⁴⁹Sm were used to tag 264 m³ of diesel fuel burned by the city bus and truck fleets; 0.39 g of ¹⁵⁰Sm were used to tag 106 m³ of residential heating oil. Picogram amounts of the tracers were determined simultaneously by thermal-ionization mass spectrometry in fine particles collected within the city at signal-to-noise ratios as large as 6000. These results demonstrate the feasibility of tracing particles from multiple combustion sources with stable, separated isotopes.     

Washout ratios of nitrate,non-sea-salt sulfate and sea-salt on Virginia key,Florida and on American Samoa

On Virginia Key, Miami, Florida, 257 rainwater samples were collected on a event basis from May 1982 to April 1985. At the same site, 171 aerosol samples were collected throughout 1984. All of these samples were analyzed for nitrate, non-sea-salt (NSS) sulfate and sodium to assess the temporal variations in the concentrations and to determine the washout ratios of each of the constituents. The annual volume-weighted mean concentrations in rainwater are: nitrate—0.51 μg ml⁻¹; NSS sulfate—0.74 μg ml⁻¹; Na—1.93 μg ml⁻¹. Only sodium exhibited a significant seasonal cycle; its concentrations were markedly higher during the winter. In aerosols, the mean concentrations are: nitrate—1.9 μg m⁻³; NSS sulfate—2.8 μg m³; Na—3.7 μg m⁻³. Nitrate and NSS sulfate exhibit consistent seasonal cycles with concentrations being significantly higher during the winter and spring. We estimate that wet deposition accounts for the majority of the total fluxes of each constituent: 80% for nitrate, 95 % for NSS sulfate, and 67% for Na. Annual washout ratios at Virginia Key arc similar for nitrate and NSS sulfate, 330 and 290, respectively. That for Na is about a factor of two higher, 550. Comparable long-term ratios were calculated for American Samoa based on aerosol data from the SEAREX program and rainwater data from the National Atmospheric Deposition Program: 270 for nitrate, 420 for NSS sulfate, and 520 for Na. The comparability of the Virginia Key and Samoa results suggest that these ratios may be applicable over a wide area of the world ocean. Estimates from nonconcurrent data for the washout ratios at Bermuda were factors of two to four higher. Regression equations for washout ratio vs event rainfall (logW = loga + blogR) at Virginia Key were essentially the same for all three constituents with ‘a’ ranging from 1100 to 1300 and ‘b’ ranging from −0.26 to −0.29. The coefficients for American Samoa were markedly different: ‘a’ ranged from 2900 to 3600 and ‘b’ ranged from −0.51 to −0.56.     

Floodplain methylmercury biomagnification factor higher than that of the contiguous river (South River, Virginia USA)

Mercury biomagnification on the South River floodplain (Virginia, USA) was modeled at two locations along a river reach previously modeled for methylmercury movement through the aquatic trophic web. This provided an opportunity to compare biomagnification in adjoining trophic webs. Like the aquatic modeling results, methylmercury-based models provided better prediction than those for total mercury. Total mercury Food Web Magnification Factors (FWMF, fold per trophic level) for the two locations were 4.9 and 9.5. Methylmercury FWMF for the floodplain locations were higher (9.3 and 25.1) than that of the adjacent river (4.6). Previous speculation was not resolved regarding whether the high mercury concentrations observed in floodplain birds was materially influenced by river prey consumption by riparian spiders and subsequent spider movement into the trophic web of the adjacent floodplains. Results were consistent with a gradual methylmercury concentration increase from contaminated floodplain soil, to arthropod prey, and finally, to avian predators.     

Influence of air mass source region on nanoparticle events and hygroscopicity in central Virginia,U.S.

During autumn, 2006, variation in the frequency of aerosol nucleation events, as inferred from nanoparticle growth events, and associated hygroscopicity were investigated as a function of air mass transport history at a mixed deciduous forest in central Virginia, U.S. Above-canopy size distributions of aerosols between 0.012 and 0.700 μm diameter, size-resolved particle hygroscopicity at eight dry diameters between 0.012 and 0.400 μm, and cloud condensation nuclei (CCN) activity were characterized. Air mass back trajectories were clustered to identify source regions. Growth events were most frequent in fast-moving air masses (mean = 9 m s^?1) that originated over the north central U.S. Under these flow regimes, mean values for preexisting sub-μm aerosol number concentrations (4700 cm^?3), corresponding surface area (142 μm² cm^?3), air temperature (6.2 °C), and relative humidity (RH, 49.4%) were relatively low compared to other regimes. Under stagnant flow conditions (mean = 3 m s^?1), mean number concentrations were higher (>6000 cm^?3) and size fractions <0.1 μm diameter exhibited enhanced hygroscopicity compared to other source regions. These results indicate that precursors emitted into relatively clean, cold, and dry air transported over the southeastern U.S. reacted to form condensable intermediates that subsequently produced new aerosols via nucleation and growth. This pathway was an important source for CCN. During events in October, nanoparticles were produced in greater numbers and grew more rapidly compared to November and December.     

Influence of seedling roots, environmental factors and soil characteristics on soil CO2 efflux rates in a 2-year-old loblolly pine (Pinus taeda L.) plantation in the Virginia Piedmont

To understand the role of managed forests in carbon sequestration an understanding of factors controlling soil CO2 efflux will be necessary. This study examined the influence of seedling roots, environmental factors, nutrient availability, and soil characteristics on soil CO2 efflux patterns in a 2-year-old pine plantation in the Virginia Piedmont. Efflux rates were measured both near the base of seedlings and midway between rows in plots that had received fertilization and mulch treatments in a factorial combination. Soil CO2 efflux rates were consistently higher near the base of seedlings, fertilization increased seedling growth with no significant effect on rates. and mulching increased winter efflux rates. In a regression analysis of seasonal soil CO2 efflux, soil temperature explained 42.2% of the variance followed by the interaction of soil temperature and moisture and of soil temperature and plot position, which together explained an additional 9.8% of the observed variance in seasonal rates. During March 2000 measurements, the spatial pattern of soil CO2 efflux between plots was most influenced by differences in soil nitrogen and pine root biomass. Furthermore, spatial differences observed in mean annual efflux rates were found to be highly influenced by the amount of soil coarse fragments in the upper soil profile.