Workshop on the Intercomparison of Methodologies for Soil NOx Emissions: Summary of Discussion and Research Recommendations

A workshop on the intercomparison of methodologies for soil NO_x emissions was held on March 14-15, 1994 at North Carolina State University (NCSU) in Raleigh, North Carolina, in preparation for a field experiment tentatively scheduled for May-June, 1995 involving measurement of rural site NO_x emissions. The workshop was sponsored jointly by the U.S. Environmental Protection Agency (EPA) and NCSU. Representatives from several agencies will participate in the experiment, including the EPA, NASA, NOAA, DOE, NCAR, Atmospheric Science from the University of Maryland, and Atmospheric Sciences and Soil Sciences from NCSU. Approximately 50 workshop attendees, which included national experts on all aspects of flux measurement technologies, met for a day and a half to discuss techniques for measuring soil NO_x (= NO + NO₂) emissions and to suggest how to best incorporate these techniques into a field experiment to compare NO_x measuring methodologies. The need for more knowledge in the area of soil NO_x emissions is related to the uncertainty of the relationship between rural NO_x emissions and the production of tropospheric ozone. In particular, the role of nitrogen-based fertilizers spread over rural agricultural areas in the production or emission of NO_x is not well documented. To determine the best way to document and model these relationships, a full experimental comparison of NO_x emission measurement techniques over a rural agricultural area is needed. Thus, it was recommended that a study of the intercomparison of methodologies for soil NO_x emissions (both intensive field experiments and analysis) should be undertaken. The primary goal of this study will be to relate chamber techniques to micrometeorological flux estimates of NO_x. The study should include (i) an intensive four-to-six-week experiment for the intercomparison of methodologies for soil NO_x emissions, (ii) and soil and air quality characterization of the experimental site.     

Dry Deposition of Ammonia at Environmental Concentrations on Selected Plant Species

The deposition velocity of NH₃ on six plant species at environmental concentrations has been studied in a dynamic plant gas exchange reactor. The total resistance to the transport of NH₃ was studied. The aerodynamic resistance was determined directly by NH₃ gas absorption in aqueous solutions at environmental concentrations in a two-phase gradientless reactor modeling the transfer processes through the stomata in a leaf. The concentration of NH₃ in the gas phase ranged from 50 to 1000 ppb and the temperature varied from 25 to 30°C. The results for the deposition velocity for NH₃, during the day, varied from 0.3 to 1.3 cm/s. The deposition velocities at night were about one order of magnitude smaller. These results are compared with estimates from the Frdssling equation which consistently yields higher values of the same order of magnitude. To determine accurate atmospheric transport models or global budget models, a variable deposition velocity should be used to account for the diurnal and seasonal variations in the surface resistance.     

Establishing the link between ammonia emission control and measurements of reduced nitrogen concentrations and deposition

In the context of international efforts to reduce the impactsof atmospheric NH₃ and NH₄ ⁺ (collectively, NH_x), it is important to establish the link between NH₃emissions and monitoring of NH_x concentrations and deposition. This is equally relevant to situations where NH₃emissions changes are certain (e.g. due to changed source sectoractivity), as to cases where NH₃ abatement technologies havebeen implemented. Correct interpretation of adequate atmosphericmeasurements is essential, since monitoring data provide the onlymeans to evaluate trends in regional NH₃ emissions.These issues have been reviewed using available measurements and modelling from nine countries. In addition to historic datasets,the analysis here considers countries where NH₃ source sector activity changed (both increases and decreases) and countries where NH₃ abatement policies have been implemented.In The Netherlands an `ammonia gap' was identified between the expected reduction and results of monitoring, and was attributedinitially to ineffectiveness of the abatement measures. The analysis here for a range of countries shows that atmospheric interactions complicate the expected changes, particularly sinceSO₂ emissions have decreased at the same time, while at manysites the few years of available data show substantial inter-annual variation. It is concluded that networks need to beestablished that speciate between NH₃ and aerosol NH₄ ⁺, in addition to providing wet deposition, and sample at sufficient sites for robust regional estimates to be established. Such measurements will be essential to monitor compliance of the international agreements on NH₃ emission abatement.     

Liquid crystallinity of levan/water/starch solutions

Transmitted light measurements performed with a UV-visible spectrophotometer were used to characterize how starch affects the position of boundaries on the phase diagram for dilute aqueous solutions of levan (a branched polymer of fructose). Data were collected in the range 15 to 70°C; the minimum concentrations required for separation of a nematic phase and the minimum concentration required for a fully nematic solution were identified within this range. While hard interactions (repulsion between rod-like molecular segments) dictate the formation of a liquid crystalline phase at and above ambient temperature in the absence of starch, soft interactions become more significant as solutions are cooled toward ambient when starch is present. Small amounts of starch might be used as a filler to modify the mechanical properties (while retaining the process-related benefits) of levan films cast from liquid crystalline solution.     

1999年委内瑞拉阿维拉山北坡入海型泥石流

委内瑞拉阿维拉山呈东一西走向，北坡濒临加勒比海．１９９９年１２月１６日，阿维拉山北坡２０多条沟谷暴发泥石流，使沿海的城镇、村庄、港口、公路及各种设施遭到毁灭性破坏，造成数万人死亡，直接经济损失超过刀亿美元．泥石流发生在森林植被良好的山区，具低频率和群发性特征，规模大，直接入海．分析这次泥石流灾害，对我国的防灾减灾工作具有启示意义．     

Ammonia assessment from agriculture: U.S. status and needs

Recent studies suggest that human activities accelerate the production of reactive nitrogen on a global scale. Increased nitrogen emissions may lead to environmental impacts including photochemical air pollution, reduced visibility, changes in biodiversity, and stratospheric ozone depletion. In the last 50 yr, emissions of ammonia (NH3), which is the most abundant form of reduced reactive nitrogen in the atmosphere, have significantly increased as a result of intensive agricultural management and greater livestock production in many developed countries. These agricultural production practices are increasingly subject to governmental regulations intended to protect air resources. It is therefore important that an accurate and robust agricultural emission factors database exist to provide valid scientific support of these regulations. This paper highlights some of the recent work that was presented at the 2006 Workshop on Agricultural Air Quality in Washington, D.C. regarding NH3 emissions estimates and emission factors from agricultural sources in the U.S. and Europe. In addition, several best management practices are explored as the scientific community attempts to maximize the beneficial use of reactive nitrogen while simultaneously minimizing negative environmental impacts.     

Organic Compounds in Cloud Water and their Deposition at a Remote Continental Site

Some organic compounds (alkylbenzene, chlorinated hydrocarbons and poiycyclic aromatic hydrocarbons) in clouds have been determined from samples collected above the canopy of a coniferous forest. The cloud samples were collected during 1987 and 1988 at Mt. Mitchell State Park, North Carolina, a remote high elevation (～2006 m MSL) continental site. Concentrations of the organic chemicals in clouds were in the range of 0.2 to ～200 ng mL^-1; and their estimated deposition rates via clouds were found to range from 1.58 * 10⁴ to 4.67 * 10⁶ ng m^-2 yr^-1. Great variations in concentrations were found which can best be explained, based on 72 hour back trajectory analysis, by different source locales and moving air masses. The concentration of these chemicals exceeded their water solubility as predicted by Henry's Law, suggesting that clouds are an excellent scavenger of organic chemicals in the ambient environment.     

Particulate matter pollution in the coal-producing regions of the Appalachian Mountains: Integrated ground-based measurements and satellite analysis

This study integrates the relationship between measured surface concentrations of particulate matter 10 μm or less in diameter (PM₁₀), satellite-derived aerosol optical depth (AOD), and meteorology in Roda, Virginia, during 2008. A multiple regression model was developed to predict the concentrations of particles 2.5 μm or less in diameter (PM_2.5) at an additional location in the Appalachia region, Bristol, TN. The model was developed by combining AOD retrievals from Moderate Resolution Imaging Spectro-radiometer (MODIS) sensor on board the EOS Terra and Aqua Satellites with the surface meteorological observations. The multiple regression model predicted PM_2.5 (r² = 0.62), and the two-variable (AOD-PM_2.5) model predicted PM_2.5 (r² = 0.4). The developed model was validated using particulate matter recordings and meteorology observations from another location in the Appalachia region, Hazard, Kentucky. The model was extrapolated to the Roda, VA, sampling site to predict PM_2.5 mass concentrations. We used 10 km x 10 km resolution MODIS 550 nm AOD to predict ground level PM_2.5. For the relevant period in 2008, in Roda, VA, the predicted PM_2.5 mass concentration is 9.11 ± 5.16 μg m^-3 (mean ± 1SD).

Implications: This is the first study that couples ground-based Particulate Matter measurements with satellite retrievals to predict surface air pollution at Roda, Virginia. Roda is representative of the Appalachian communities that are commonly located in narrow valleys, or “hollows,” where homes are placed directly along the roads in a region of active mountaintop mining operations. Our study suggests that proximity to heavy coal truck traffic subjects these communities to chronic exposure to coal dust and leads us to conclude that there is an urgent need for new regulations to address the primary sources of this particulate matter.