Ernesto C. Tuazon

Trace pollutant concentrations in a multiday smog episode in the California South Coast Air Basin by long path length Fourier transform infrared spectroscopy.

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A kilometer pathlength Fourier-transform infrared system for the study of trace pollutants in ambient and synthetic atmospheres.

Abstract A Fourier-transform infrared (FT-i.r.) system operable at pathlengths up to 2 km has been constructed for the detection and measurement of trace contaminants in the ambient atmosphere and in controlled smog formation studies. The long optical path is achieved by the use of an eight-mirror multiple reflection cell with a 22.5-m base path. The design, construction and use of this novel foldedpath optical system are described in detail. In preliminary ambient air measurements at Riverside, California, during the period August–October, 1976, ppb concentrations of formaldehyde, nitric acid, formic acid and ammonia (in addition to O 3 and PAN) were measured in ambient air.

The nitric acid shootout: field comparison of measurement methods

Eighteen instruments for measuring atmospheric concentrations of nitric acid were compared in an eight day field study at Pomona College, situated in the eastern portion of the Los Angeles Basin, in September 1985. The study design included collocated and separated duplicate samplers, and the analysis by each laboratory of a set of quality assurance filters, so that the experimental variability could be distinguished from differences due to measurement methods. For all sampling periods, the values for nitric acid concentrations reported by the different instruments vary by as much as a factor of four. The differences among measurement techniques increase with nitric acid loading, corresponding to a coefficient of variation of 40%. In contrast, samplers of the same design operated by the same group show variability of 11–27 %. Overall, the highest reported concentrations are observed with the filter packs and lower concentrations are observed by the annular denuders and tunable diode laser absorption spectrometers. When the nitric acid concentrations are high enough to be detected by the FTIR, the FTIR values are close to those obtained by the denuder difference method and to the mean value from the other sampler groups. In the absence of a reference standard for the entire study, measurement methods are compared to the average of four denuder difference method samplers (DDM). Filter pack samplers are higher than the DDM for both daytime and night-time sampling. Two different filter packs using Teflon® prefilters are higher than the DDM by factors of 1.25 and 1.4. The results from the three annular denuders do not agree; the ratios of means to the DDM value are 1.0,0.8 and 0.6. For the transition flow reactor method and for two dichotomous samplers operated as denuder difference samplers, the ratio of means to the DDM are 1.09 and 0.93, respectively. The tunable diode laser absorption spectrometers gave lower daytime and higher night-time readings compared to the DDM, especially during the last three days of the study. Averaged over the entire measurement period, the daytime ratio of TDLAS to DDM is 0.8 and the night-time ratio is 1.7.

.alpha.-Dicarbonyl yields from the NOx-air photooxidations of a series of aromatic hydrocarbons in air

The yields of the ring-cleavage products glyoxal, methylglyoxal and biacetyl from the reactions of OH radicals with benzene, toluene, o-, m- and p-xylene and 1,2,3-, 1,2,4- and 1,3,5-trimethylbenzene in the presence of part-per-million concentrations of NO have been determined in one atmosphere of air using in-situ long pathlength Fourier-transform infrared absorption spectroscopy and differential optical absorption spectroscopy with supplementary gas-chromatographic analyses. The yields of glyoxal and methylglyoxal were respectively: from toluene, 0.105 plus or minus 0.019 and 0.146 plus or minus 0.006; from o-xylene, 0.087 plus or minus 0.012 and 0.246 plus or minus 0.020; from m-xylene, 0.086 plus or minus 0.011 and 0.319 plus or minus 0.009; from p-xylene, 0.225 plus or minus 0.039 and 0.105 plus or minus 0.034; from 1,2,3-trimethylbenzene, 0.058 plus or minus 0.008 and 0.152 plus or minus 0.025; and from 1,2,4-trimethylbenzene, 0.048 plus or minus 0.005 and 0.357 plus or minus 0.017.

Spectroscopic identification and measurement of gaseous nitrous acid in dilute auto exhaust

We report here the direct spectroscopic detection of gaseous nitrous acid (HONO) in exhaust emissions from certain light duty motor vehicles (LDMV). Co-pollutants such as nitrogen dioxide (NO2), formaldehyde (HCHO), benzaldehyde (C6H5CHO) and sulfur dioxide (SO2) were also readily determined. Nitric oxide (NO) was measured too, but with reduced accuracy. To avoid possible artifactual formation of HONO on the surfaces of conventional dilution and sampling systems (e.g. Federal and California constant volume sampling systems), an instrument was developed consisting of a multiple reflection cell without walls coupled to a u.v. differential optical absorption spectrometer (DOAS), the entire system being placed in the open air ~ 2 m from the tailpipe of the LDMV. At an optical path of 31.2 m, detection limits (in parts per 109, ppb) were: HONO-12; HCHO-78; C6H5CHO-13; NO2-57; and SO2-11. With this instrument, HONO levels observed in diluted exhaust ranged from nondetectable (< 12 ppb) for a 1982 California car with an effective 3-way catalyst (and associated low NOx emissions), to ~ 300 ppb for a heavily used 1974 station wagon having high NOx emissions and run on leaded gasoline. While the number of LDMV tested was too small for statistical treatment, our results show that the older portion of the total LDMV population (i.e. without current emission control devices) may be a significant primary source of gaseous HONO, a key precursor to photochemical air pollution and an inhalable nitrite.

Products of the gas-phase reactions of O(3 P) atoms and O3 with α-pinene and 1,2-dimethyl-1-cyclohexene

Products and mechanisms of the gas-phase reactions of O(3P) atoms and O3 with the cycloalkenes α-pinene and 1,2-dimethyl-1-cyclohexene have been investigated at 296±2 K and 740 torr total pressure, using gas chromatography and in situ atmospheric pressure ionization tandem mass spectrometry. The O(3P) atom reaction with α-pinene led to the formation of α-pinene oxide and two isomeric C10H16O ketones with yields of 0.77±0.06, 0.18±0.03, and 0.06±0.02, respectively. The O(3P) atom reaction with 1,2-dimethyl-1-cyclohexene produced 1,2-dimethyl-1-cyclohexene oxide with a yield of 0.51±0.16. Product studies of the O3 reactions in the presence of cyclohexane as an OH radical scavenger showed the formation of α-pinene oxide and pinonaldehyde from α-pinene with yields of 0.021±0.007 and 0.143±0.024, respectively, and the formation of 1,2-dimethyl-1-cyclohexene oxide, 5-oxohexanal, and 2,7-octanedione from 1,2-dimethyl-1-cyclohexene with yields of 0.020±0.006, 0.19±0.05, and 0.07±0.02, respectively. No evidence for the formation of O(3P) atoms from either the reactions of α-pinene or 1,2-dimethyl-1-cyclohexene with O3 was obtained (with estimated O(3P) atom yields of <0.03 and <0.04, respectively), and the formation of the epoxides is attributed to a direct reaction. An OH radical formation yield from the 1,2-dimethyl-1-cyclohexene reaction of 1.02±0.16 was measured using 2-butanol to scavenge the OH radicals and form 2-butanone. Experiments to elucidate the formation route(s) to 2,7-octanedione and pinonaldehyde were carried out, and it is postulated that these carbonyl products are formed from reactions of the thermalized biradicals with water vapor.

Simultaneous absolute measurements of gaseous nitrogen species in urban ambient air by long pathlength infrared and ultraviolet-visible spectroscopy

Abstract Two new long pathlength spectrometers, utilizing 25-m basepath multiple reflection optical systems, were employed for the first time during an intercomparison of measurement methods for atmospheric nitrogenous species held at Claremont, CA, 11–19 September 1985. Measurement of nitrogenous species using these closed optical path systems, as opposed to single pass systems extending several kilometers, permit the resulting in situ absolute spectroscopic data to serve as benchmark values for point monitors employing denuders or filter packs. The FT-IR spectrometer was operated at a total pathlength of 1150 m and spectral resolution of 0.125 cm −1 , with corresponding detection sensitivities of 160 nmolem −3 for HNO 3 and 60 nmole m −3 for NH 3 (4 and 1.5 ppb, respectively). Concurrent measurements of HONO, NO 2 and NO 3 radicals were conducted with the differential optical absorption spectrometer operated at 800 m total pathlength with detection limits of 24, 160 and 0.8 nmole m −3 (0.6, 4 and 0.02 ppb) for HONO, NO 2 , and NO 3 radicals, respectively.

Experimentally determined kinetic isotope effects in the reaction of CH4 with Cl: Implications for atmospheric CH4

We report experimental values for the carbon and hydrogen kinetic isotope effects (KIEs) in the reaction of CH4 with Cl at temperatures between 273 and 350 K. Isotope ratio mass spectrometry was utilized to measure 13CH4/12CH4 and CH3D/CH4 ratios on samples taken from a 5870- L reaction chamber. At 299 K, kc12/kc13 = 1.0621±0.0001 (2σ) and kh/kd = 1.474±0.020 (2σ). For both KIEs, the ratio decreased with increasing temperature over the range studied. These results agree well with experimental studies using tunable diode laser absorption spectroscopy and FTIR absorption spectroscopy and with a recent theoretically-calculated set of values.

Tropospheric transformation products of a series of hydrofluorocarbons and hydrochlorofluorocarbons

The products of the Cl-atom initiated reactions of a series of hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) in air have been investigated at 298 K and one atmosphere (740 Torr total pressure) of air. The products observed and quantified and their yields (%) were as follows: from CHF2Cl (HCFC-22), C(O)F2 (100%); from CHFCl2 (HCFC-21), C(O)FCl (100%); from CH2FCl (HCFC-31), HC(O)F (100%); from CH3F (HFC-41), HC(O)F (100%); from CH3CFCl2 (HCFC-141b), C(O)FCl (100%); from CH3CF2Cl (HCFC-142b), C(O)F2 (100%); from CH3CHF2 (HFC-152a), C(O)F2 (92%); from CHCl2CF3 (HCFC-123), CF3C(O)Cl (98%); from CHFClCF3 (HCFC-124), CF3C(O)F (101%); and from CHF2CF3 (HFC-125), C(O)F2 (∼100%). The reaction mechanisms are discussed.

Tropospheric degradation products of CH2FCF3 (HFC-134a)

AbstractChlorine atom-initiated photooxidations of CH2FCF3 (HFC-134a) in O2-N2 diluent were carried out to identify the products formed from the