International programme on chemical safety

This paper discusses methods for ranking photochemical ozone formation reactivities of volatile organic compounds (VOCs). Photochemical mechanisms for the atmospheric reactions of 118 VOCs were used to calculate their effects on ozone formation under various NOx conditions in model scenarios representing 39 different urban areas. Their effects on ozone were used to derive 18 different ozone reactivity scales, one of which is the Maximum Incremental Reactivity (MIR) scale used in the new California Low Emission Vehicle and Clean Fuel Regulations. These scales are based on three different methods for quantifying ozone impacts and on six different approaches for dealing with the dependencies of reactivity on NOx. The predictions of the scales are compared, the reasons for their similarities and differences are discussed, and the sensitivities of the scales to NOx and other scenario conditions are examined. Scales based on peak ozone levels were highly dependent on NOx, but those based on integrated ...

Development of Ozone Reactivity Scales for Volatile Organic Compounds

The nitrate radical: Physics, chemistry, and the atmosphere

Large quantities of non-methane hydrocarbons (NMHCs) are emitted into the atmosphere from vegetation1,2 A recent inventory by Lamb et al2 indicates that the emission of natural hydrocarbons is significant compared to that of anthropogenic NMHCs in most regions of the United States Because of their chemical activity, the natural NMHCs can play important parts in the formation of trace gases, such as ozone (O3), peroxyacetyl nitrate (PAN) and oxygenated secondary hydrocarbons3–5, which contribute to regional-scale air pollution6 and may be harmful to crops and forest7–9 The impact of natural hydrocarbons on the formation of O3 in the atmosphere has been discussed previously4–13 In general, it has been concluded that their impact is small14–16 But lack of data on the ambient concentrations of key photochemical species and an incomplete analysis of the photochemistry has prevented a definitive evaluation of the impact of natural NMHCs on rural O3 Here we report on concentrations of key trace gases measured concurrently at a rural site in the eastern USA during the summer of 1986 and a modelling study conducted to analyse these measurements This study demonstrates that natural NMHCs can have a significant impact on ozone formation in rural air

Models and observations of the impact of natural hydrocarbons on rural ozone

The atmospheric chemistry of organic nitrates

Photochemical aspects of air pollution. Review

Atmospheric oxidation of chlorinated ethylenes

Methyl tertiary butyl ether (MTBE) has been proposed and is being used as an additive to increase the octane of gasoline without the use of tetraethyl lead and alkylbenzenes. The present experiments have been performed to examine the kinetics and mechanisms of the atmospheric removal of MTBE. The kinetics of the reaction of OH with MTBE was examined by using a relative rate technique in which photolysis of methyl nitrite was used as the source of OH. With n-butane as the reference compound a value of (2.99 ± 0.12) × 10−12 cm3 molecule−1 s−1 at a temperature of 298 K was obtained for the rate constant. The products (and product yields) for the OH reaction with MTBE in the presence of NOx were also determined and found to be t-butyl formate (0.68 ± 0.05), methyl acetate (0.14 ± 0.02), acetone (0.026 ± 0.003), t-butanol (0.062 ± 0.009), and formaldehyde (0.48 ± 0.05) in mols/mol MTBE converted. The OH rate constant for the major product formed, t-butyl formate was also measured and found to be (7.37 ± 0.05) × 10−13 cm3 molecule−1 s−1. Mechanisms to rationalize the formation of the products are presented.

The photooxidation of methyl Tertiary butyl ether

Hydrogen peroxide formation from formaldehyde photooxidation and its presence in urban atmospheres

In May of 1976 a three-day study was undertaken in St. Petersburg/Tampa, the Everglades, and Miami areas to assess the importance of naturally emitted hydrocarbons to ozone production. Some samples were collected within inches of citrus trees in an effort to observe the occurrence of natural terpene hydrocarbon emissions. Other samples were collected in remote areas to determine hydrocarbon composition and to investigate natural hydrocarbon contribution to the overall hydrocarbon burden. No significant natural hydrocarbon contribution was observed in any of the collected samples. The C/sub 10/ terpene hydrocarbons were below the limit of detectability of 1 ppb carbon. The meteorological conditions during this study were not conducive for the buildup of high hydrocarbon concentration, and low ozone levels were observed. The results suggest that natural hydrocarbon emissions are not as important as anthropogenic sources of hydrocarbon in the formation of ambient ozone. 12 references, 3 figures, 1 table.

Joseph J. Bufalini

Papers

Photochemical aspects of air pollution. Review

Atmospheric oxidation of chlorinated ethylenes

The photooxidation of methyl Tertiary butyl ether

Hydrogen peroxide formation from formaldehyde photooxidation and its presence in urban atmospheres

Ambient air hydrocarbon concentrations in Florida