Analysis of the processing of Nashville urban emissions on July 3 and July 18, 1995

Abstract

Abstract. This paper analyzes data obtained on July 3 and 18, 1995, during the summer 1995 Southern Oxidant Study (SOS) field campaign. In a previous paper [Nunnermacker et al., 1998] we analyzed measurements of key species that contribute to formation of O3 in the Nashville urban plume and presented a semiquantitative picture of O3 production in the plume from the point of emission to locations where no net O3 was being formed. In this paper we use a box model constrained by observed concentrations of stable species to obtain a detailed mechanistic description of the instantaneous processing of urban emissions at various times in the chemical evolution of the urban plume. Instantaneous ozone production rates and efficiencies with respect to NOx and to primary radical production are examined. At high NOx concentrations in the fresh urban plume the O3 production rate was found to be directly proportional to the hydrocarbon to NOx reactivity ratio. At lower NOx concentrations, corresponding to the mature urban plume and the background atmosphere, the O3 production rate was found to be directly proportional to the NOx concentration and independent of the hydrocarbon reactivity. NOx was found to be most efficiently used for ozone production at low NOx concentrations. In contrast, the efficiency with which the system uses primary radicals was found to be very low at low NOx concentrations and to peak at a NOx concentration of approximately 4 ppbv. A sensitivity study of the instantaneous O3 production rates to changes in NOx or hydrocarbon concentrations showed that the instantaneous 03 production rate at the center of the urban plume, when half of the urban NOx emissions had been processed, is hydrocarbon sensitive. However, 03 production becomes NOx sensitive as the plume matures.

Characterizing ozone production and response under different meteorological conditions in Mexico City

“…Over 90% of the radicals are removed through the radical-NO x reactions (Fig. 6d) compared to less than 10% via the radical-radical reactions, implying that the midday O 3 formation is VOC-limited (Sillman, 1995;Kleinman et al, 1997;Daum et al, 2000). Q and K VOC values (which are closely related to each other) are higher during the "Cold Surge" and "O 3 -North" episodes than during the "O 3 -South" episode, leading to higher P(O x ) values in the former.…”

Characterizing ozone production in the Mexico City Metropolitan Area: a case study using a chemical transport model

“…When NO x increases and passes the turnaround level, defined as the NO x concentration at which O 3 production rate P(O 3 ) reaches a maximum, P(O 3 ) is expected to decrease. Based on the concept of radical budget (OH+HO 2 +RO 2 ), Sillman et al (1990), Kleinman et al (1997), and Daum et al (2000) derived analytical solutions for O 3 photochemical production in terms of O 3 precursors and other oxidation products that can be readily measured. These analytical equations have been widely used in box models to calculate O 3 production rates based on observations.…”

Ozone production in the New York City urban plume

“…where kt is the average rate constant for HO2, RO2 + NO, kerr is an effective rate constant for peroxide formation, and Q is the rate of radical production [Kleinman et al, 1995]. Equation ( varies by a factor of 2.5 in response to differences in 03 and HCHO.…”