The impact of bark beetle infestations on monoterpene emissions and secondary organic aerosol formation in western North America

Over the last decade, extensive beetle outbreaks in western North America have destroyed over 100 000 km2 of forest throughout British Columbia and the western United States. Beetle infestations impact monoterpene emissions through both decreased emissions as trees are killed (mortality effect) and increased emissions in trees under attack (attack effect). We use 14 yr of beetle-induced tree mortality data together with beetle-induced monoterpene emission data in the National Center for Atmospheric Research (NCAR) Community Earth System Model (CESM) to investigate the impact of beetle-induced tree mortality and attack on monoterpene emissions and secondary organic aerosol (SOA) formation in western North America. Regionally, beetle infestations may have a significant impact on monoterpene emissions and SOA concentrations, with up to a 4-fold increase in monoterpene emissions and up to a 40% increase in SOA concentrations in some years (in a scenario where the attack effect is based on observed lodgepole pine response). Responses to beetle attack depend on the extent of previous mortality and the number of trees under attack in a given year, which can vary greatly over space and time. Simulated enhancements peak in 2004 (British Columbia) and 2008 (US). Responses to beetle attack are shown to be substantially larger (up to a 3-fold localized increase in summertime SOA concentrations) in a scenario based on bark-beetle attack in spruce trees. Placed in the context of observations from the IMPROVE network, the changes in SOA concentrations due to beetle attack are in most cases small compared to the large annual and interannual variability in total organic aerosol which is driven by wildfire activity in western North America. This indicates that most beetle-induced SOA changes are not likely detectable in current observation networks; however, these changes may impede efforts to achieve natural visibility conditions in the national parks and wilderness areas of the western United States.National Science Foundation (U.S.) (ATM- 0929282)National Science Foundation (U.S.) (ATM-0939021)National Science Foundation (U.S.) (ATM-0938940)United States. Dept. of Energy. Office of Scienc

The Restyled Federal Rules of Evidence

A lightly edited transcript of the Symposium held at the William & Mary School of Law on October 28, 2011

The Restyled Federal Rules of Evidence

A lightly edited transcript of the Symposium held at the William & Mary School of Law on October 28, 2011

A review of the anthropogenic influence on biogenic secondary organic aerosol

Because of the climate and air quality effects of organic aerosol, it is important to quantify the influence of anthropogenic emissions on the aerosol burden, both globally and regionally, and both in terms of mass and number. Methods exist with which the fractions of organic aerosol resulting directly from anthropogenic and biogenic processes can be estimated. However, anthropogenic emissions can also lead to an enhancement in secondary organic aerosol formation from naturally emitted precursors. We term this enhanced biogenic secondary organic aerosol (eBSOA). Here, we review the mechanisms through which such an effect may occur in the atmosphere and describe a work flow via which it may be quantified, using existing measurement techniques. An examination of published data reveals support for the existence of the enhancement effect

Kinetics and mechanisms of nonmetal redox reactions of oxyhalogens

The mechanisms of several oxidation/reduction reactions of oxyhalogen species are presented. Bromine chloride (BrCl) catalyzes the decomposition of hypochlorous acid/hypobromous acid (HOCl/HOBr) mixtures. BrCl reacts with hypochlorite ion (OCl−) to form BrOCl, which hydrolyzes to chlorite (ClO2−) and bromide (Br −) ions. Bromite ion (BrO2−) is formed via HOBr disproportionation. Rapid reactions of HOCl/BrO2 − and HOBr/ClO2− produce bromate (BrO3−) and chlorate (ClO3 −) ions, respectively. The study of the HOCl/HOBr decomposition is enabled by the ion chromatography (IC). The preparation of HOCl/HOBr reaction mixtures for IC requires removal of HOCl and HOBr from the samples. Three dehalogenating species, phenol, 4-hydroxybenzoic acid, and sulfite ion, enable ion chromatographic analysis. The reduction of BrO2− by sulfite ion (k = 3.0 × 107 M−1 s−1) occurs through the OBr + transfer reaction to sulfite ion, with subsequent general-acid catalyzed hydrolysis of OBrSO3−. Conversely, ClO 2− does not react with sulfite, and the reaction is not general-acid catalyzed. Chlorite and S(IV) react via an oxygen-atom transfer where k(ClO2−/SO 2) = 6.26 × 106 M−1 s −1 and k(ClO2−/SO 3H−) = 5.5 M−1 s−1 . The reaction of HOBr with nitrite ion (NO2− ) proceeds by a bromine-atom transfer reaction. HOBr, NO2 −, and H+ are in equilibrium with nitryl bromide, BrNO2 (K = 2.73 × 108 M −2). BrNO2 is detected spectrophotometrically where ϵ(260 nm) = 956 M−1 cm−1. BrNO2 reacts rapidly with NO2− (k = 6.9 × 103 M−1 s−1) to form Br− and N2O 4 and can dissociate to form NO2+ and Br − (k = 18 s−1). Rapid reactions of N2O4 and NO2+ with water produce NO3− as a final product. Nitrite levels above 100 mM cause a suppression of the observed rate constant. This suggests that N2O4 hydrolysis occurs by reversible heterolytic dissociation into NO2+ and NO2 −