Thomas Pierce

A biogenic hydrocarbon emission inventory for the U.S.A. using a simple forest canopy model

Abstract A biogenic hydrocarbon emission inventory system, developed for acid deposition and regional oxidant modeling, is described, and results for a U.S. emission inventory are presented. For deciduous and coniferous forests, scaling relationships are used to account for canopy effects upon solar radiation temperature, humidity and wind speed as a function of height through the canopy. Leaf temperature is calculated iteratively from a leaf energy balance as a function of height through the canopy. The predicted light and temperature levels are used with mean emprical emission rate factors and laboratory emission algorithms to predict hydrocarbon emission rates. For application to a U.S. inventory, diurnal emission fluxes of isoprene, α-pinene, other monoterpenes adn otehr hydrocarbons are predicted for eight land cover classes by state climatic division by month. The total U.S. emissions range from 22 to 50 Tg yr −1 depending upon the formulation of different emission rate factors. In the case where the forest canopy model is not used, the isoprene emissions increase by 50% and terpene emissions increase by 6%. In case study analyses, the predicted leaf temperatures were within 1–2°C of observed for a deciduous forest, and predicted emissions were within a factor of two of observations. Further evaluation of the inventory using field measurements is required to determine the overall accuracy of the emission estimates.

Influence of increased isoprene emissions on regional ozone modeling

The role of biogenic hydrocarbons on ozone modeling has been a controversial is- sue since the 1970s. In recent years, changes in biogenic emission algorithms have resulted in large increases in estimated isoprene emissions. This paper describes a recent algorithm, the second generation of the Biogenic Emissions Inventory System (BEIS2). A sensitivity analysis is performed with the Regional Acid Deposition Model (RADM) to examine how increased isoprene emissions generated with BEIS2 can influence the modeling of elevated ozone concentrations and the response of ozone to changes to volatile organic compound (VOC) and nitrogen oxide (NOx) emissions across much of eastern North America. In- creased isoprene emissions are found to produce a predicted shift in elevated ozone concen- trations from VOC sensitivity to NOx sensitivity over many areas of eastern North America. Isoprene concentrations measured near Scotia, Pennsylvania, during the summer of 1988 are compared with RADM estimates of isoprene and provide support for the veracity of the higher isoprene emissions in BEIS2, which are about a factor of 5 higher than BEIS 1 during warm, sunny conditions.

Isoprene fluxes measured by enclosure, relaxed eddy accumulation, surface layer gradient, mixed layer gradient, and mixed layer mass balance techniques

Isoprene fluxes were estimated using eight different measurement techniques at a forested site near Oak Ridge, Tennessee, during July and August 1992. Fluxes from individual leaves and entire branches were estimated with four enclosure systems, including one system that controls leaf temperature and light. Variations in isoprene emission with changes in light, temperature, and canopy depth were investigated with leaf enclosure measurements. Representative emission rates for the dominant vegetation in the region were determined with branch enclosure measurements. Species from six tree genera had negligible isoprene emissions, while significant emissions were observed for Quercus, Liquidambar, and Nyssa species. Above-canopy isoprene fluxes were estimated with surface layer gradients and relaxed eddy accumulation measurements from a 44-m tower. Midday net emission fluxes from the canopy were typically 3 to 5 mg C m−2 h−1, although net isoprene deposition fluxes of −0.2 to −2 mg C m−2 h−1 were occasionally observed in early morning and late afternoon. Above-canopy CO2 fluxes estimated by eddy correlation using either an open path sensor or a closed path sensor agreed within ±5%. Relaxed eddy accumulation estimates of CO2 fluxes were within 15% of the eddy correlation estimates. Daytime isoprene mixing ratios in the mixed layer were investigated with a tethered balloon sampling system and ranged from 0.2 to 5 ppbv, averaging 0.8 ppbv. The isoprene mixing ratios in the mixed layer above the forested landscape were used to estimate isoprene fluxes of 2 to 8 mg C m−2 h−1 with mixed layer gradient and mixed layer mass balance techniques. Total foliar density and dominant tree species composition for an approximately 8100 km2 region were estimated using high-resolution (30 m) satellite data with classifications supervised by ground measurements. A biogenic isoprene emission model used to compare flux measurements, ranging from leaf scale (10 cm2) to landscape scale (102 km2), indicated agreement to within ±25%, the uncertainty associated with these measurement techniques. Existing biogenic emission models use isoprene emission rate capacities that range from 14.7 to 70 μg C g−1 h−1 (leaf temperature of 30°C and photosynthetically active radiation of 1000 μmol m−2 s−1) for oak foliage. An isoprene emission rate capacity of 100 μg C g−1 h−1 for oaks in this region is more realistic and is recommended, based on these measurements.

PC-BEIS: A Personal Computer Version of the Biogenic Emissions Inventory System

The U.S. Environmental Protection Agency’s Biogenic Emissions Inventory System (BEIS) has been adapted for use on IBM-compatible personal computers (PCs). PC-BEIS estimates hourly emissions of Isoprene, α-plnene, other monoterpenes, and unidentified hydrocarbons for any county In the contiguous United States. To run the program, users must provide hourly data on ambient temperature, relative humidity, wind speed, cloud cover, and a code that Identifies the particular county. This paper provides an overview of the method used to calculate biogenic emissions, shows an example application, and gives information on how to obtain a copy of the program.

The sensitivity of regional ozone modeling to biogenic hydrocarbons

The sensitivity of regional ozone concentrations to biogenic hydrocarbons in the northeastern United States has been examined using an Eulerian grid photochemical model having a horizontal resolution of 18 km. A 6-day period during which observed ozone concentrations exceeded 200 ppb was simulated. Detailed estimates of biogenic nonmethane hydrocarbon (NMHC) emissions were included in the model simulations. Overall, biogenic emissions were of the same order of magnitude as anthropogenic emissions. Approximately 33% of the biogenic inventory was in the form of isoprene, with the remainder of the NMHC in the form of monoterpenes and unidentified NMHC. Three model sensitivity runs were analyzed in which biogenic emissions, and then anthropogenic hydrocarbon emissions, were selectively removed from the emissions data set. Episode maximum predicted ozone concentrations were compared for each simulation, and a detailed chemical analysis was performed on two trajectories within the modeling domain. The analysis showed that the relative impact of biogenic compared to anthropogenic hydrocarbons on ozone generation varied spatially over the model domain. The biogenic influence on ozone was greatest in western and southern sections of the domain, particularly in the Ohio Valley, while the anthropogenic influence was greatest in the urbanized Northeast Corridor and industrial Great Lakes area.

UNITED STATES LAND USE INVENTORY FOR ESTIMATING BIOGENIC OZONE PRECURSOR EMISSIONS

The U.S. Geological Survey’s (USGS) EROS (Earth Resources Observation System) Data Center’s (EDC) 1-km classified land cover data are combined with other land use data using a Geographic Information System (GIS) to create the Biogenic Emissions Landcover Database (BELD). The land cover data are being used to estimate biogenic emissions in the contiguous United States. These emissions include volatile organic compound (VOC) emissions from vegetation and nitric oxide (NO) from soils. The EDC data are used predominately in the western United States, while other sources, such as the U.S. Department of Agriculture’s Census of Agriculture and the U.S. Forest Service Eastwide Forest Inventory and Analysis Database (EWDB), are used in the eastern United States. The EROS Data Center land cover classifications must be used with caution in heterogenous areas. Emission factors vary drastically by specific crop and tree genera, and mixed classes in the EDC scheme may not always accurately reflect the actual crop/genus...

Reassessment of biogenic volatile organic compound emissions in the Atlanta area

Abstract Localized estimates of biogenic volatile organic compound (BVOC) emissions are important inputs for photochemical oxidant simulation models. Since forest tree species are the primary emitters of BVOCs, it is important to develop reliable estimates of their areal coverage and BVOC emission rates. A new system is used to estimate these emissions in the Atlanta area for specific tree genera at hourly and county levels. The U.S. Department of Agriculture, Forest Service Forest Inventory and Analysis data and an associated urban vegetation survey are used to estimate canopy occupancy by genus in the Atlanta area. A simple canopy model is used to adjust photosynthetically active solar radiation at five vertical levels in the canopy. Lraf temperature and photosynthetically active radiation derived from ambient conditions above the forest canopy are then used to drive empirical equations to estimate genus level emission rates of BVOCs vertically through forest canopies. These genera-level estimates are then aggregated to county and regional levels for input into air quality models and for comparison with (1) the regulatory model currently used and (2) previous estimates for the Atlanta area by local researchers. Estimated hourly emissions from the three approaches during a documented ozone event day are compared. The proposed model yields peak diurnal isoprene emission rates that are over a factor of three times higher than previous estimates. This results in total BVOC emission rates that are roughly a factor of two times higher than previous estimates. These emissions are compared with observed emissions from forests of similar composition. Possible implications for oxidant events are discussed.

Evaluation of forest canopy models for estimating isoprene emissions

During the summer 1992, environmental and biogenic hydrocarbon emissions data were collected in a mixed hardwood forest at scales ranging from leaf to canopy to the mixed layer for the purpose of investigating issues related to the scale-up of leaf or branch level emission measurements to regional emission inventories. Results from canopy measurements are compared to several different forest canopy emission models. These range in complexity from a no-canopy effects method to the PC-BEIS canopy profile method to a numerical forest canopy radiative transfer model. The investigation includes a model-to-model intercomparison of predicted canopy environmental parameters including photosynthetically active radiation (PAR) and leaf temperature. The work is seeking to evaluate relatively simple modeling approaches for use in regional emission inventories using field data and more sophisticated numerical models.

Environmental variables controlling nitric oxide :emissions from agricultural soils in the southeast united states

Fluxes of nitric oxide (NO) were measured during the summer of 1994 (12 July to l 1 August) in the Upper Coastal Plain of North Carolina in a continuing effort to characterize NO emissions from intensively managed agricultural soils in the southeastern United States. Previous work during a similar time of year on the same soil type was characterized by severe moisture stress conditions. The summer of 1994 provided a more diverse weather pattern and as a result represented a set of measurements more typical of soil temperature and soil moisture relationships for the southeastern United States. In order to ascertain NO flux response to fertilization and crop type, measurements were made on fields with three distinct fertilizer practices and crop types, namely corn, cotton, and soybean. Average NO fluxes were 21.9 _ 18.6, 4.3 + 3.7, and 2.1 + 0.9ngNm-2s -1, respectively, for corn, cotton, and soybean. NO flux increased exponentially with soil temperature when soil water content was not limiting ( > 30%o Water Filled Pore Space (%oWFPS)). During conditions when soil water content was limiting, NO flux was inhibited and had no relationship with soil temperature. Above a value of 30% WFPS, increasing soil water content had no effect on NO emissions (the upper limit of %WFPS could not be estimated due to a lack of data in this regime). Below 30% WFPS, increasing soil moisture increased NO production and lower soil moistures led to decreased NO flux. Increased nitrogen fertilization rates led to higher NO fluxes. However, differences in physiological growth stages between crops confound extractable nitrogen values as decompo- sing root biomass in the mature corn crop added an undetermined amount of available nitrogen to the soil. Interactions between soil water content, fertilizer application, and soil temperature make it very difficult to predict day-to-day variations of NO flux from our data. There appears to be no simple relation between NO flux and the environmental variables measured in Clayton, NC during the summer of 1994. Copyright

Natural emissions of oxidant precursors

This paper provides an overview of the sources, the estimation methodology, and the relative amounts of natural hydrocarbon and NOx emissions. The most recent estimate of natural nonmethane hydrocarbon (NMHC) emissions for the United States is 28 Tg yr−1. This compares with 20 Tg yr−1 for anthropogenic NMHC sources. The southeastern and southcentral portions of the United States account for approximately 43% of the annual U.S. natural NMHC estimate. These emissions exhibit strong diurnal and seasonal dependencies related to temperature, solar radiation, and active biomass. Forests are the primary vegetative source of hydrocarbons. The major sources of natural NOX emissions in North America are biomass burning, lightning, and microbial activity in soil. We present a comparison of hourly gridded NOX emissions from lightning, soil, and man-made sources for the northeastern United States. We also provide results from preliminary investigations of the sensitivity of O3 predictions from the U.S. Environmental Protection Agencys Regional Oxidant Model to natural NMHC and nitric oxide emissions.