Geoffrey W. Harris

Observations of nitrous acid in the Los Angeles atmosphere and implications for predictions of ozone-precursor relationships.

Direct measurements of nitrous acid (HONO) were made in downtown Los Angeles and Riverside, CA, during night and early morning hours of July/August 1980 using a long-path differential optical absorption spectrometer. Up to 8 ppb of HONO were observed in Los Angeles, approximately twice the maximum levels previously measured in Riverside during the summer of 1979. Possible sources of the observed HONO are discussed. If the observed HONO levels are included in initial NO, concentration, EKMA isopleth calculations predict that more rigorous control of NO, emissions (especially a t low HC/NO, levels) or of hydrocarbons emissions is necessary to reduce ozone maxima by a given amount compared with predictions based on calculations neglecting initial HONO. Moreover, including HONO in the starting NO, leads to predictions of accelerated rates of oxidant production which results in much larger predicted O3 doses at elevated O3 levels. For example, the predicted O3 dosage at levels above 0.3 ppm ozone in the case of NMHC = 1 ppm and [NO,], = 0.12 ppm is increased by over 250% when 10 ppb of HONO is taken to be initially present.

Rates and temperature dependences of the reaction of hydroxyl radical with isoprene, its oxidation products, and selected terpenes.

Absolute rate constants determined by using the flash photolysis-resonance fluorescence technique are reported for the reactions of hydroxyl radicals with isoprene, ..cap alpha.., and ..beta..-pinene, methyl vinyl ketone, and methacrolein in the temperature range 297-424 K, and with methylglyoxal at 297 K. These results contribute to a more quantitative understanding of the tropospheric fate of gas-phase biomass-related organics and serve as input to models of the chemistry of the natural troposphere.

Rate constants for the reaction of OH radicals with CH3CN, C2H5CN AND CH2CH-CN in the temperature range 298–424 K

Abstract Rate constants for the reactions of OH with CH 3 CN, CH 3 CH 2 CN and CH 2 CH-CN have been measured to be 5.86 × 10 −13 exp(−1500 ± 250 cal mole −1 / RT ), 2.69 × 10 −13 exp(−1590 ± 350 cal mole −1 / RT and 4.04 × 10 −12 cm 3 molecule −1 s −1 , respectively in the temperature range 298–424 K. These results are discussed in terms of the atmospheric lifetimes of nitrfles.

Temperture dependance of the reaction OH + SO2 + M → HSO3 + M FOR M = Ar AND SF6

Abstract Absolute rate constants k1bi have been determined, using a flash-photolysis— resonance-fluorescence technique, for the atmospherically important reaction of OH radicals with SO2 for M = Ar and SF6 over the temperature range 298–424 K at total pressures from 98–653 Torr. At ≈650 Torr total pressure, the Arrhenius expressions kbi1(M = Ar) = 1.16 × 10−14 × exp[ (2370 ± 300) RT ] cm3 molecule−1 s−1, kbi1(M = SF6) = 1.27 × 10−1 exp[ (1495± 300) RT ] cm3 molecule−1s−1 were obtained where the (negative) activation energies are in cal/mole. The rate constants at 298 K. and ≈650 Torr are k1bi(M = Ar) = (6.49 ± 0.84) × 10−13 cm−3 molecule−1 s−1 and kbi1(M = SF6) = (1.61 ± 0.22) × 10−12 cm3 molecule−1 s−1. A value of k1bi(M = N2) = 4.0 × 10−13 exp( 1900 RT ) cm3 molecule−1 s−1at approximately atmospheric pressure was estimated from these results with kbi1(M = N2) = 1.0 × 10−12 cm3 molecule−1 s−1 at ≈650 Torr total pressure and 298 K, in good agreement with a recent evaluation.

Interactions between diesel emissions and gaseous copollutants in photochemical air pollution: Some health implications

Abstract A complete assessment of the health effects of diesel emissions must take into account the possible chemical transformations (and associated biological impacts) of particulate organic matter (POM) due to reactions with the many gaseous copollutants which have now been unambiguously demonstrated to be present in atmospheres burdened by photochemical air pollution. These copollutants include the “trace” species, nitric (HNO 3 ) and nitrous (HONO) acids, the nitrate radical (NO 3 ), formaldehyde (H 2 CO) and formic acid (HCOOH), as well as the criteria pollutants, ozone (O 3 ) and nitrogen dioxide (NO 2 ). Techniques for establishing the atmospheric concentrations of the trace pollutants (and their spatial and temporal variations) are briefly described, and we present results of investigations into the reactions of polycyclic aromatic hydrocarbons (PAH) coated on filters and exposed to ambient concentrations of O 3 and NO 2 . Environmental health implications of these results are discussed and include the potential for sampling “artifacts” and their possible effects on the correlation (or lack thereof) between ambient PAH levels and urban lung cancer rates, as well as the problems associated with understanding the appropriate POM “dose” to be employed in animal testing and assessments of impacts on human health.

Measurement of NO2 and HNO3 in diesel exhaust gas by tunable diode laser absorption spectrometry

A tunable diode laser absorption spectrometer (TDLAS) has been used to make real-time measurements of NO/sub 2/ and HNO/sub 3/ in diesel engine exhaust. Teflon filters in the sample line protected the optics from exhaust particulates. Nitric acid and NO/sub 2/ were measured in the range of 40-800 ppbv and 1-30 ppmv, respectively. The mixing ratio of HNO/sub 3/ was found to decrease as engine load increased and to increase with engine speed. The HNO/sub 3/ levels exhibited slow response (10-30 min) both for changes in engine operating condition and when controlled spikes of HNO/sub 3/ were added to the diluted exhaust gas flow. NO/sub 2/ concentrations reached steady values within 5 min of changes in operating conditions. The data indicate that the observed HNO/sub 3/ is present in the exhaust stream immediately after dilution and is not produced by subsequent reactions of NO/sub x/. There was no correlation between the variations in particulate nitrate and the gas-phase HNO/sub 3/ with load and engine speed. 8 references, 5 figures, 2 tables.