Allan L. Lazrus

Bio: Allan L. Lazrus is an academic researcher from National Center for Atmospheric Research. The author has contributed to research in topics: Sulfate & Stratosphere. The author has an hindex of 25, co-authored 41 publications receiving 2887 citations.

Chemical mechanisms of acid generation in the troposphere

Abstract: Diverse chemical pathways in the troposphere convert sulphur and nitrogen oxides and organic compounds into acids, involving the gas phase, the liquid phase (cloud, fog and rain water) and, possibly, certain suspended aerosols. The rates of acid generation are critically affected by the extent of generation of the oxidizing species and the kinetics of the reactions. Precipitation in the eastern United States shows a strong seasonal variation in deposition of sulphates in contrast to nitrates. Computer simulations can now rationalize the observed seasonal trends. Recent tropospheric measurements of gaseous hydrogen peroxide show that this gas is a major oxidant leading to sulphuric acid generation in cloud water.

Automated fluorimetric method for hydrogen peroxide in atmospheric precipitation

Abstract: An automated analytical technique for the determination of hydrogen peroxide (H/sub 2/O/sub 2/) in the liquid phase has been developed. The chemistry of this technique is based on the reaction of H/sub 2/O/sub 2/ with horseradish peroxidase and p-hydroxyphenylacetic acid (POPHA). The resulting reaction forms the fluorescent dimer of POPHA. By use of conventional fluorescence detection techniques a detection limit of 1.2 x 10/sup -8/ M (0.4 ppbm) H/sup 2/O/sup 2/ is obtained for a 1.5-mL aqueous sample. The coefficient of variation is 0.66% at 1.6 x 10/sup -6/ M (53 ppbm). The analytical chemical reaction responds stoichiometrically to both H/sup 2/O/sup 2/ and organic hydroperioxides. To discriminate H/sup 2/O/sup 2/ from organic hydroperioxides, a novel dual-channel chemical flow system has been devised to separately determine total hydroperioxides and organic hydroperioxides. The concentration of H/sup 2/O/sup 2/ is determined by the difference between these two measurements. The system has been tested extensively for potential interferences commonly found in environmental aqueous samples, and none has been observed. 17 references, 4 figures, 2 tables.

Automated fluorometric method for hydrogen peroxide in air

Abstract: A fluorometric method for measuring H/sub 2/O/sub 2/ vapor in air utilizes peroxidase enzyme to catalyze the reaction in which hydroperoxides cause dimerization of (p-hydroxyphenyl)acetic acid. In a second channel, H/sub 2/O/sub 2/ is selectively decomposed by catalase so that the fluorescence signal is due only to organic hydroperoxides. The difference between the two signals is a measure of H/sub 2/O/sub 2/ vapor. The H/sub 2/O/sub 2/ vapor is collected by means of a glass coil though which air and water flow concurrently. The coefficient of variation is 0.5% at 2.5 parts per billion by volume. The standard deviation of the base line is 10 parts per trillion by volume (pptv) under laboratory conditions. This standard deviation has varied between 3 and 33 pptv during ground-based field missions, and was 70 pptv on aircraft flights. Thirty seconds is required for the signal to change from 10 to 90% of its maximum value. 13 references, 4 figures, 1 table.

Aqueous phase oxidation of sulfur(IV) by hydrogen peroxide, methylhydroperoxide, and peroxyacetic acid

Abstract: The aqueous phase oxidation kinetics of sulfur(IV) by hydrogen peroxide, methylhydroperoxide, and peroxyacetic acid have been investigated over the pH range 4.0–5.2 for hydrogen peroxide and methylhydroperoxide and 2.9–5.8 for peroxyacetic acid. The reagent concentrations used in these studies were in the micromolar range. In the cases of hydrogen peroxide and peroxyacetic acid, 1 mol of sulfate was produced for each mole of peroxide consumed. In the case of methylhydroperoxide, 0.73±0.04 mol of sulfate, and 0.27±0.04 mol of the methylsulfate were produced for each mole of peroxide consumed. The experimentally determined rate laws for the three reactions are given by d[peroxide]/dt = k[H+] [peroxide] [S(IV)]. The third order rate constants, k, for the three reactions were determined to be 7.2±2.0×107 M−2s−1 for hydrogen peroxide (18°C), 1.7±0.4×107 M−2s−1 for methylhydroperoxide (23°C), and 3.5±1.3 ×107 M−2s−1 for peroxyacetic acid (18°C). The oxidation kinetics of aqueous S(IV) by peroxyacetic acid also contained a second-order term over the pH range investigated in this study, first-order in both peroxyacetic acid and S(IV) concentrations. The rate constant k′ for this term was determined to be 6.1±2.6×102 M−1s−1. Temperature dependence studies over the range 6°–25°C yielded activation energies of 31.6±1.3 kJ/mol for methylhydroperoxide and 33.2±0.7 kJ/mol for peroxyacetic acid.

Lead and other metal ions in United States precipitation

Abstract: ATMOSPHERIC PRECIPITATION SAMPLES COLLECTED BY A NATIONWIDE NETWORK OF 32 STATIONS THROUGHOUT THE UNITED STATES WERE ANALYZED FOR LEAD, ZINC, COPPER, IRON, MANGANESE AND NICKLE BY ATOMIC ABSORPTION. VALUES FOR EACH STATION, AVERAGED OVER APPROXIMATELY SIX MONTHS DURING 1966 AND 1967, INDICATE HUMAN ACTIVITY AS THE PRIMARY SOURCE OF THESE MATERIALS IN ATMOSPHERIC PRECIPITATION. THE STUDY REVEALS THAT THE NORTHWEST PORTION OF THE U.S. IS CONSPICUOUSLY LOW IN CONTAMINATION; THE NORTHEAST IS RELATIVELY HIGH; AND THE SOUTHWEST AND SOUTHEAST VARY FROM LOW TO MODERATE, DEPENDING ON THE METAL. THE CONCENTRATION OF LEAD IN PRECIPITATION WAS FOUND TO BE CORRELATED WITH THE AMOUNT OF GASOLINE CONSUMED IN THE AREA IN WHICH THE SAMPLE WAS COLLECTED. THE OVERALL MEAN CONCENTRATIONS OF THE METALS IN PRECIPITATION ARE COMPARED WITH ANALOGOUS VALUES IN SURFACE WATER SUPPLIES. /AUTHOR/

Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature)

Abstract: . Reactive gases and aerosols are produced by terrestrial ecosystems, processed within plant canopies, and can then be emitted into the above-canopy atmosphere. Estimates of the above-canopy fluxes are needed for quantitative earth system studies and assessments of past, present and future air quality and climate. The Model of Emissions of Gases and Aerosols from Nature (MEGAN) is described and used to quantify net terrestrial biosphere emission of isoprene into the atmosphere. MEGAN is designed for both global and regional emission modeling and has global coverage with ~1 km2 spatial resolution. Field and laboratory investigations of the processes controlling isoprene emission are described and data available for model development and evaluation are summarized. The factors controlling isoprene emissions include biological, physical and chemical driving variables. MEGAN driving variables are derived from models and satellite and ground observations. Tropical broadleaf trees contribute almost half of the estimated global annual isoprene emission due to their relatively high emission factors and because they are often exposed to conditions that are conducive for isoprene emission. The remaining flux is primarily from shrubs which have a widespread distribution. The annual global isoprene emission estimated with MEGAN ranges from about 500 to 750 Tg isoprene (440 to 660 Tg carbon) depending on the driving variables which include temperature, solar radiation, Leaf Area Index, and plant functional type. The global annual isoprene emission estimated using the standard driving variables is ~600 Tg isoprene. Differences in driving variables result in emission estimates that differ by more than a factor of three for specific times and locations. It is difficult to evaluate isoprene emission estimates using the concentration distributions simulated using chemistry and transport models, due to the substantial uncertainties in other model components, but at least some global models produce reasonable results when using isoprene emission distributions similar to MEGAN estimates. In addition, comparison with isoprene emissions estimated from satellite formaldehyde observations indicates reasonable agreement. The sensitivity of isoprene emissions to earth system changes (e.g., climate and land-use) demonstrates the potential for large future changes in emissions. Using temperature distributions simulated by global climate models for year 2100, MEGAN estimates that isoprene emissions increase by more than a factor of two. This is considerably greater than previous estimates and additional observations are needed to evaluate and improve the methods used to predict future isoprene emissions.

The Chemistry of Water Treatment Processes Involving Ozone, Hydrogen Peroxide and Ultraviolet Radiation

Abstract: Advanced oxidation processes are defined as those which involve the generation of hydroxyl radicals in sufficient quantity to affect water purification. The theoretical and (practical yield of OH from O3 at high pH, 03/H202, O3/UV and H2O2/UV systems is reviewed. New data is presented which illustrates the importance of direct photolysis in the O3/UV process, the effect of the H202:03 ratio in the O3/H2O2 process, and the impact of the low extinction coefficient of H2O2 in the H202/UV process.

The second generation regional acid deposition model chemical mechanism for regional air quality modeling

Abstract: A state-of-the-art gas phase chemical mechanism for modeling atmospheric chemistry on a regional scale is presented. The second generation Regional Acid Deposition Model (RADM2) gas phase chemical mechanism, like its predecessor RADM1, is highly nonlinear, since predicted ozone, sulfate, nitric acid and hydrogen peroxide concentrations are complicated functions of NO{sub x} and nonmethane hydrocarbon concentrations. The RADM2 chemical mechanism is an upgrade of RADM1 in that (1) three classes of higher alkanes are used instead of one, (2) a more detailed treatment of aromatic chemistry is used, (3) the two higher alkene classes now represent internal and terminal alkenes, (4) ketones and dicarbonyl species are treated as classes distinct from aldehydes, (5) isoprene is now included as an explicit species, and (6) there is a more detailed treatment of peroxy radical-peroxy radical reactions. As a result of these improvements the RADM2 mechanism simulates the concentrations of peroxyacetyl nitrate, HNO3, and H{sub 2}O{sub 2} under a wide variety of environmental conditions. Comparisons of RADM2 mechanism with the RADM1 mechanism predictions and selected environmental chamber experimental results indicate that for typical atmospheric conditions, both mechanisms reliably predict O{sub 3}, sulfate and nitric acid concentrations. The RADM2 mechanism gives lower and presumably moremore » realistic predictions of H{sub 2}O{sub 2} because of its more detailed treatment of peroxy radical-peroxy radical reactions.« less

Visibility: Science and Regulation

Abstract: The 1999 Regional Haze Rule provides a context for this review of visibility, the science that describes it, and the use of that science in regulatory guidance The scientific basis for the 1999 regulation is adequate The deciview metric that tracks progress is an imperfect but objective measure of what people see near the prevailing visual range The definition of natural visibility conditions is adequate for current planning, but it will need to be refined as visibility improves Emissions from other countries will set achievable levels above those produced by natural sources Some natural events, notably dust storms and wildfires, are episodic and cannot be represented by annual average background values or emission estimates Sulfur dioxide (SO2) emission reductions correspond with lower sulfate (SO4 2−) concentrations and visibility im-provements in the regions where these have occurred Non-road emissions have been growing more rapidly than emissions from other sources, which have remained