ChemInform Abstract: Rate of Gas Phase Association of Hydroxyl Radical and Nitrogen Dioxide.

Abstract. Nitrous acid (HONO) mixing ratios for the Houston metropolitan area were simulated with the Community Multiscale Air Quality (CMAQ) model for an episode during the Texas Air Quality Study (TexAQS) II in August/September 2006 and compared to in-situ MC/IC (mist-chamber/ion chromatograph) and long path DOAS (Differential Optical Absorption Spectroscopy) measurements at three different altitudes. Several HONO sources were accounted for in simulations, such as gas phase formation, direct emissions, nitrogen dioxide (NO2*) hydrolysis, photo-induced formation from excited NO2* and photo-induced conversion of NO2 into HONO on surfaces covered with organic materials. Compared to the gas-phase HONO formation there was about a tenfold increase in HONO mixing ratios when additional HONO sources were taken into account, which improved the correlation between modeled and measured values. Concentrations of HONO simulated with only gas phase chemistry did not change with altitude, while measured HONO concentrations decrease with height. A trend of decreasing HONO concentration with altitude was well captured with CMAQ predicted concentrations when heterogeneous chemistry and photolytic sources of HONO were taken into account. Heterogeneous HONO production mainly accelerated morning ozone formation, albeit slightly. Also HONO formation from excited NO2 only slightly affected HONO and ozone (O3) concentrations. Photo-induced conversion of NO2 into HONO on surfaces covered with organic materials turned out to be a strong source of daytime HONO. Since HONO immediately photo-dissociates during daytime its ambient mixing ratios were only marginally altered (up to 0.5 ppbv), but significant increase in the hydroxyl radical (OH) and ozone concentration was obtained. In contrast to heterogeneous HONO formation that mainly accelerated morning ozone formation, inclusion of photo-induced surface chemistry influenced ozone throughout the day.

Download Full-text

Multivariate modelling of the rate constant of the gas-phase reaction of haloalkanes with the hydroxyl radical

The Science of The Total Environment ◽

10.1016/0048-9697(91)90187-j ◽

1991 ◽

Vol 109-110 ◽

pp. 307-325 ◽

Cited By ~ 18

Author(s):

Maria Livia Tosato ◽

Claudio Chiorboli ◽

Lennart Eriksson ◽

Jorgen Jonsson

Keyword(s):

Hydroxyl Radical ◽

Gas Phase ◽

Rate Constant ◽

Phase Reaction ◽

Gas Phase Reaction ◽

Multivariate Modelling

Download Full-text

Reactivity of Oxygen Radicals [HO•, RO•, HOO•, ROO-, and RC(O)O•]

Oxygen Chemistry ◽

10.1093/oso/9780195057980.003.0009 ◽

1992 ◽

Author(s):

Donald T. Sawyer ◽

R. J. P. Williams

Keyword(s):

Oxygen Atom ◽

Hydroxyl Radical ◽

Gas Phase ◽

Oxygen Radicals ◽

Oxygen Radical ◽

Superoxide Ion ◽

Radical Reactivity ◽

The Family ◽

Hydrocarbon Substrates

Oxygen radicals are defined as those molecules that contain an oxygen atom with an unpaired, nonbonding electron (e.g., HO·). Although triplet dioxygen (·O2·) and superoxide ion (O2 - ·) come under this definition, their nonradical chemistry dominates their reactivity, which is discussed in Chapters 6 (·O2·) and 7 (O2-·). The hydroxyl radical (HO·) is the most reactive member of the family of oxygen radicals [HO·, RO·, ·O·, HOO·, ROO·, and RC(O)O·], and is the focus of most oxygen radical research. In the gas phase the dramatic example of oxygen radical reactivity with hydrocarbon substrates is combustion, which is initiated by HO· (or RO· or MO·) and propagated by ·O2· and ·O·.

Download Full-text