Effect of Chemical Product Yield Uncertainties on Reactivities of VOCs and Emissions from Reformulated Gasolines and Methanol Fuels

Abstract

To account for differences in exhaust composition that arise with the use of fuels other than conventional gasoline, California regulations apply reactivity adjustment factors (RAFs) to emissions standards for new motor vehicles. The RAFs are based on estimates of the sensitivity of ozone formation to each of the individual organic compounds in the exhaust. In this study, uncertainties have been estimated for the incremental reactivities of individual organic compounds and for RAFs for motor vehicle exhaust, accounting for uncertainties in chemical rate parameters and product yields and for variability in exhaust composition. Uncertainties (1σ) in incremental reactivities of individual compounds range from about 25 to 75% of mean estimates and are typically about 10% higher than previous estimates obtained by considering independent rate parameters as the only source of uncertainty in the chemical mechanism. The incremental reactivities of relatively rapidly reacting compounds are sensitive to the peroxy radical yields in their primary oxidation reactions. RAF values of 0.87 ( 0.11 (1σ) and 0.42 ( 0.06, respectively, are calculated for exhaust emissions from a test gasoline with low aromatics and low olefins content, and from an 85% methanol, 15% gasoline blend. The RAF values show little sensitivity to product yield uncertainties.*

Kinetic investigation of gas‐phase reactions between the OH‐radical and o‐, m‐, p‐ethyltoluene and n‐nonane in air

“…Some organic compounds, in particular aromatic compounds, are used as additives in reformulated gasoline. Ethyltoluene is one such additive in unleaded gasoline 1, 2. As a consequence these hydrocarbons are emitted in larger quantities by cars running with unleaded fuel than by those running with leaded fuel 3.…”

III – Validation des schémas chimiques

“…Dans ce but, la contribution du paramètre p j à l'incertitude globale est estimée selon [14,15] : V ij = σ 2 pj × s 2 ij . Les tests de sensibilité réa -lisés par Gao et al [14] L'incertitude globale des concentrations simulées induite par les incertitudes associées aux différents paramètres du schéma chimique est généralement quantifiée sur la base d'une analyse de Monte Carlo [15,18,19]. L'incertitude sur chaque paramètre du schéma chimique est caractérisée par une loi de distribution.…”

“…La figure 3 présente quelques exemples de profils d'ozone obtenus par une analyse de Monte Carlo. Pour une période de 12 heures, l'écart type calculé sur les concentrations maximales d'ozone est de l'ordre de 20 à 50 % [15,18,19]. L'incertitude calculée sur les profils de H 2 O 2 est significativement plus élevée (30 à 200 %), de même pour le PAN (40 à 70 %).…”

Monte Carlo uncertainty and sensitivity analysis of the CACM chemical mechanism

“…For instance, Dunker [1981, 1984], Milford et al [1992], and Gao et al [1995] used direct decoupled methods; Rabitz et al [1983] and Rabitz and Hales [1995] employed the Green's Function or Adjoint Green's Function methods; whereas Carmichael et al [1997] favored automatic differentiation techniques. Monte Carlo methods that examine uncertainties in chemical parameters have been applied also to gas‐phase chemistry and photochemical box models [ Stolarski et al , 1978; Ehhalt et al , 1979; Thompson and Stewart , 1991; Gao et al , 1995; Yang et al , 1996]. Monte Carlo methods are widely used because they can be applied to problems with a large number of input parameters.…”