No abstract

Under the National Ambient Air Quality Standards (NAAQS), put in place as a result of the Clean Air Amendments of 1990, three regions in the state of Utah are in violation of the NAAQS for PM10 and PM2.5 (Salt Lake County, Ogden City, and Utah County). These regions are susceptible to strong inversions that can persist for days to weeks. This meteorology, coupled with the metropolitan nature of these regions, contributes to its violation of the NAAQS for PM during the winter. During January-February 2009, 1-hr averaged concentrations of PM10-2.5, PM2.5, NO(x), NO2, NO, O3, CO, and NH3 were measured. Particulate-phase nitrate, nitrite, and sulfate and gas-phase HONO, HNO3, and SO2 were also measured on a 1-hr average basis. The results indicate that ammonium nitrate averages 40% of the total PM2.5 mass in the absence of inversions and up to 69% during strong inversions. Also, the formation of ammonium nitrate is nitric acid limited. Overall, the lower boundary layer in the Salt Lake Valley appears to be oxidant and volatile organic carbon (VOC) limited with respect to ozone formation. The most effective way to reduce ammonium nitrate secondary particle formation during the inversions period is to reduce NO(x) emissions. However, a decrease in NO(x) will increase ozone concentrations. A better definition of the complete ozone isopleths would better inform this decision. Implications: Monitoring of air pollution constituents in Salt Lake City, UT, during periods in which PM2.5 concentrations exceeded the NAAQS, reveals that secondary aerosol formation for this region is NO(x) limited. Therefore, NO(x) emissions should be targeted in order to reduce secondary particle formation and PM2.5. Data also indicate that the highest concentrations of sulfur dioxide are associated with winds from the north-northwest, the location of several small refineries.

The hydrological response due to potential CO,~forced climate change in the Black Hills of South Dakota was investigated using modelling techniques that include variations to atmospheric CO,, temperature, and precipitation. The Soil and Water Assessment Tool (SWAT) was used to model the 427 km 2 Spring Creek basin hydrology and simulate the impact of potential climate change. As expected, modelling results of precipitation and temperature change demonstrated that increased temperature caused a decrease in water yield while increased precipitation caused an increase in water yield. Increased CO, and precipitation caused the largest increase in yield. Modelling results of increased atmospheric CO, indicate that average annual water yield increased by W7c. This increase is attributed to a suppression of transpiration processes due to increased levels of atmospheric CO,. Simulation results demonstrate that increased concentrations of atmospheric CO, act to dampen water yield loss due to the effects of increased temperature or decreased precipitation alone.Key words climate change impacts; climate scenario analysis; yield changes; mathematical modelling; forest hydrology; hydrological processes; South Dakota, USA Réponse hydrologique au changement climatique dans les Collines Noires du Dakota du Sud Résumé La réponse hydrologique aux modifications potentielles du forçage climatique du au CO, dans les Collines Noires du Dakota du Sud a été étudiée grâce aux techniques de modélisation incluant des variations du CO, atmosphérique, de la température, et des précipitations. Un outil d'évaluation du sol et de l'eau (SWAT) a été utilisé pour modéliser l'hydrologie du bassin de Spring Creek (427 km 2 ) et aussi pour simuler l'impact d'une éventuelle modification du climat. La modélisation des effets d'une modification des précipitations et de la température montre que l'augmentation de la température provoque une diminution de la production d'eau alors que l'augmentation des précipitations provoque une augmentation la production d'eau. L'augmentation conjointe du CO, et des précipitations provoquent la plus importante augmentation de la production. La modélisation de l'augmentation du CO, atmosphérique montre que la production moyenne annuelle d'eau augmente alors de 16%. Cette augmentation est attribuée à la diminution de la transpiration qui est attribuable à l'augmentation du niveau de CO, atmosphérique. Les résultats des simulations démontrent que l'augmentation de la concentration du CO, atmosphérique amortissent les pertes de production de l'eau dues à l'augmentation de la température ou à la seule diminution des précipitations. Open for discussion until I August 200128 T. A. Fontaine et al.