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The concentrations of soluble nitrate are plotted against the dose asmeasured by the nitrogen oxide monitor. Error bars indicate ±1SE.linear and non-saturating with respect to increasing dose, as might be expectedfrom a purely physico-chemical processes occurring between a reactive surfacesuch as clay particles and a highly reactive compound such HNO3. It also clearlyindicates a non-biological aspect of atmospheric deposition (detailed analysis ofatmospheric deposition to soil surfaces can be found in Padgett and Bytnerowicz,2001).In contrast to the abiotic interactions of HNO3 deposition, Figure 7b shows theresults of a similar experiment using growing plant material exposed to similardoses, for similar durations – about 4 weeks. Four different shrub species wereevaluated for apparent deposition using a leaf wash method similar to that de-scribed by Bytnerowicz and Riechers (1995). In the plant experiment, not only was deposition saturating at relatively low doses, but a significant difference existed in‘washable’ NO−3 among the four species investigated. The differences in apparentdeposition velocity of HNO3 to different plant surfaces have been recognized fora decade or more (Hanson and Lindberg, 1991) although the mechanisms are notwell understood. It has been hypothesized that differences in cuticle chemistry ordifferences in leaf boundary conditions drive interspecific differences in washabledeposition, but the means for testing these hypotheses have not been available untilnow. The tendency of plant surfaces to saturate with time or exposure has alsobeen noted by others (Cadle et al. 1991).
It is has been reported as a change indeposition velocity with time, but again the mechanisms are not understood. Per-haps decreases in deposition velocity are related to surface chemical phenomenonor perhaps uptake and assimilation contribute to the apparent saturation of leavesover time. This system has enabled the testing of these types of hypothesis notpreviously testable and is now leading to new interpretations of deposition valuesand deposition effects (e.g. Padgett and Bytnerowicz, 2001; Parry, 2001).4. ConclusionsUnderstanding dry deposition of HNO3 and its resultant effects on ecosystemshas been hampered by the lack of accurate, reproducible exposures where theN species can be quantified. Many questions about the physico-chemistry of de-position, biological assimilation and measurement of HNO3 deposition remainunanswered. The fumigation system described represents a new tool for advancingour understanding of atmospheric pollution effects on terrestrial systems. Resultspresented here indicate that HNO3 concentrations and diurnal patterns that mimicambient patterns can be achieved consistently and reproducibly. The evaluationsalso highlighted the complexity of atmospheric reactions, even in simple systemssuch as the CSTRs where relatively high concentrations of NH3 due to greenhouseactivities interacted with HNO3 to form NH4NO3 aerosols. The authors welcomedirect inquiries for more specific answers to the more specific technical questions.AcknowledgementsFunding for this project was provided by USDA-NRI Grant #9701063. We thankthe University of California, Riverside and the State Air Pollution Research Centerfor facilities cooperation.ReferencesBytnerowicz, A. and Fenn, M. E.: 1996, ‘Nitrogen deposition in California forests: A review’,Environ. Pollut. 92, 127–146.
摘要：浓硝酸蒸汽污染是空气污染的一个重要组成部分。干沉积的浓硝酸被认为是一个主要的贡献者对于形成地球原始资源组成成分的氮（N），但还有很多关于在表面干沉积的浓硝酸是怎么进行沉积和生物反应方面的物理化学过程的问题。用实验法检查这些过程后，一个连续搅拌釜反应器（装运箱）的熏蒸系统由此产生。这个系统允许同时在几个浓度中，在1.3米到 1.3米深进行熏蒸工作，允许同时进行许多实验单位的熏蒸。对这个系统的评估表明，这是一个适合于在几个月时间能长期暴露并且有能模仿昼夜模式中大气浓硝酸浓度的代表地区，不同程度的污染的能力。