Abstract
Nitric acid (HNO3) vapor is an important nitrogenous air pollutant responsible for increasing saturation of forests with nitrogen and direct injury to plants. The USDA Forest Service and University of California researchers have developed a simple and inexpensive passive sampler for monitoring air concentrations of HNO3. Nitric acid is selectively absorbed on 47-mm Nylasorb nylon filters with no interference from particulate NO3-. Concentrations determined with the passive samplers closely corresponded with those measured with the co-located honeycomb annular denuder systems. The PVC protective caps of standardized dimensions protect nylon filters from rain and wind and allow for reliable measurements of ambient HNO3 concentrations. The described samplers have been successfully used in Sequoia National Park, the San Bernardino Mountains, and on Mammoth Mountain in California.
Highlights
Nitric acid (HNO3) vapor, an air pollutant found in photochemical smog, affects the health of people and vegetation
Increased deposition of HNO3 may lead to eutrophication of sensitive ecosystems and contamination of surface water with nitrate (NO3-), especially in locations close to photochemical smog source areas such as mountain ranges in southern California close to Los
Nylon filters were not absorbing NO3– linearly indicating near saturation point with HNO3 (HNO3 dose of about 5700 μg/m3 × h). These results indicate that the open-ring filters would saturate after 14 days of exposure to average concentration of HNO3 of about 17 μg/m3 (6.6 ppb)
Summary
Nitric acid (HNO3) vapor, an air pollutant found in photochemical smog, affects the health of people and vegetation. Because of its very high reactivity and deposition velocity[1], HNO3 provides large amounts of nitrogen (N) to forests and other ecosystems[2]. In forests of the Los Angeles Basin mountain ranges, HNO3 provides more that 60% of the dry-deposited N to mixed conifer forests[3]. Increased deposition of HNO3 may lead to eutrophication of sensitive ecosystems and contamination of surface water with nitrate (NO3-), especially in locations close to photochemical smog source areas such as mountain ranges in southern California close to Los. Angeles[4]. While ambient concentrations of HNO3 expressed as 24-h averages did not exceed 2.1 μg/m3 in a rural European location[5] and 4.8 μg/m3 as a 12-h daytime average in the Sierra. Information on HNO3 spatial and temporal distribution in forest ecosystems of the western U.S is essential for a better under-standing of its phytotoxic potential and development of N deposition models at a landscape level
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