Robert L. Seila

Correlation of secondary organic aerosol with odd oxygen in Mexico City

> 0.9. The dependence of the observed proportionality onthe gas-phase hydrocarbon profile is discussed. Theobservationally-based correlation between oxygenatedorganic aerosol mass and odd oxygen may provide insightinto poorly understood secondary organic aerosolproduction mechanisms by leveraging knowledge of gas-phase ozone production chemistry. These results suggestthat global and regional models may be able to use theobserved proportionality to estimate SOA as a co-product ofmodeled O

Transportation-Related Volatile Hydrocarbon Source Profiles Measured in Atlanta

Abstract Samples representative of transportation-related hydrocarbon emissions were collected as part of the 1990 Atlanta Ozone Precursor Monitoring Study. Motor vehicle emissions were sampled in canisters beside a roadway in a tunnel-like underpass during periods of heavy traffic. Airport and aircraft emissions were approximated by canister samples obtained at a major airport facility. Three octane grades of gasoline were purchased from six major vendors in Atlanta. Canister samples were prepared using these fuels to approximate the whole gasoline and gasoline vapor composition of the fuels in use during the study. All samples were analyzed by gas chromatography/flame ionization detection (GC/FID) for their hydrocarbon content. Detailed speciated hydrocarbon profiles were developed from this source sampling and analysis program for use in the Chemical Mass Balance (CMB) model. Profiles presented and discussed here represent the hydrocarbon composition of emissions from a roadway, composite headspace gas...

Cryogenic preconcentration-direct FID method for measurement of ambient NMOC: refinement and comparison with GC speciation

A method for measuring total nonmethane organic compounds (NMOC) In the atmosphere has been refined to reduce measurement variability and evaluated for possible use In connection with the control of hydrocarbon emissions. The method, a simplification of the conventional gas chromatographlc (GC) speciation technique, uses cryogenic preconcentration and flame ionization detection but does not use a GC column. Tests to compare this simplified method to the GC speciation technique, using actual ambient air samples, were carried out. Test results showed that the sensitivity and precision of the simplified method approach those of the speciation technique. Other test results verified that the use of stainless steel sample canisters for collection and temporary storage of NMOC samples Is acceptable and contributes little additional variability to the method.

Determination of room temperature OH rate constants for acetylene, ethylene dichloride, ethylene dibromide, p-dichlorobenzene and carbon disulfide

A relative rate procedure was used to measure hydroxyl rate constants at room temperature in the presence of oxygen. The photolysis of methyl nitrite in the presence of nitric oxide was used to generate OH radicals. The rate of loss of the test compounds was measured relative to that of ethane (K{sub OH} = 2.74 {times} 10{sup {minus}13} cm{sup 3} molec{sup {minus}1} s{sup {minus}1}). The rates obtained at 297 {plus minus} 2 K are: acetylene = (7.8 {plus minus} 1.6) {times} 10{sup {minus}13} cm{sup 3} molec{sup {minus}1} s{sup {minus}1}, 1,2-dichloroethane (2.8 {plus minus} 0.6) {times} 10{sup {minus}13} cm{sup 3} molec{sup {minus}1} s{sup {minus}1}, 1,2-dibromoethane (2.4 {plus minus} 0.5) {times} 10{sup {minus}13} cm{sup 3} molec{sup {minus}1} s{sup {minus}1}, p-dichlorobenzene (4.3 {plus minus} 0.9) {times} 10{sup {minus}13} cm{sup 3} molec{sup {minus}1} s{sup {minus}1} and carbon disulfide (29 {plus minus} 6) {times} 10{sup {minus}13} cm{sup 3} molec{sup {minus}1} s{sup {minus}1}. Under a proposed EPA rule, this OH rate determination procedure could be used to determine if a given volatile organic will be subject to control for reduction of photochemical ozone.

Photochemical Reactivity of Perchloroethylene: A New Appraisal

Perchloroethylene (PCE), a solvent used in dry cleaning, has been suspected of contributing significantly to photochemical ozone/oxidant (O3/Ox) problems in urban atmospheres. Past evidence, however, was neither complete nor consistent. To interpret more conclusively the past evidence, and further understand PCEs role in the O3Ox problem, a smog chamber testing program was conducted. The programs objectives were: (a) to explain the mechanism of the PCE reaction in smog chamber atmospheres, and (b) to extrapolate the smog chamber findings regarding PCE reactivity to the real atmosphere. Results showed that in smog chambers, PCE reacts and forms O3/Ox following what appears to be a Cl instigated photooxidation mechanism rather than the OH initiated mechanism accepted in current smog chemistry. The evidence, collectively, strongly supported this conclusion even though the source of Cl atoms could not be identified with confidence. It was further concluded that in the real atmosphere neither the Cl instigat...

Subtractive technique for analyzing natural oleffinic hydrocarbon

Abstract The selective removal of some C10 olefinic terpenes from hydrocarbon mixtures was investigated since direct gas chromatographic analysis of mixtures of these compounds is hampered by severe peak overlaps. A HgSO4‐H2SO4 precolumn stripper was used to efficiently strip several C10 olefinic terpenes from complex mixtures of other hydrocarbons. This procedure permits investigators to identify and measure terpenes accurately both in rural forested areas and in urban areas.