Maximum Incremental Reactivity

The peak IR value of a VOC is known as its maximum incremental reactivity (MIR). The MIR of some VOCs are given in Table 16.9 and shown schematically in Fig. 16.35. (Note that the units of MIR used are grams of 03 per gram of VOC added, rather than on a molecule per C atom basis as for the IRs in Table 16.8.) Note the very low reactivity for methane, as discussed earlier. These reactivities are in generally good agreement with experimental values measured... 

TABLE 16.9 Maximum Incremental Reactivities (MIR) for Some VOCs... 

In Eq. (C) FT j is the mass fraction of compound i in the exhaust from the test fuel, Fu, is the mass fraction of compound i in the exhaust from the base fuel, and MIR, is the maximum incremental reactivity of VOC i. Thus, a specific vehicle/test fuel combination with an RAF of 1.0 is expected to have the same contribution to ozone formation (in terms of specific reactivity, grams of 03 per gram of VOC exhaust emissions) as that vehicle operating on base gasoline. An RAF < 1.0 means that 1 g of the VOC exhaust emissions will form... 

FIGURE 16.35 Maximum incremental reactivities of some organics (grams of 03 produced per gram of VOC) (data graciously provided by B. Croes, personal communication). 

This approach has also been applied to sources other than automobiles to assess the relative importance of various organics and sources. For example, Blake and Rowland (1995) used the concept of maximum incremental reactivity to assess the relative importance of various organics in Mexico City. They concluded that liquefied petroleum gas was a major contributor to ozone formation and that relatively small fractions of highly reactive alkenes in the gas contributed disproportionately to ozone formation. 

Carter, W P. L., Computer Modeling of Environmental Chamber Measurements of Maximum Incremental Reactivities of Volatile Organic Compounds, Atmos. Enciron., 29, 2513-2527 (1995). 

McNair, L. A., A. G. Russell, M. T. Odnian, B. E. Croes, and L. Kao, Airshed Model Evaluation of Reactivity Adjustment Factors Calculated with the Maximum Incremental Reactivity Scale for Transitional-Low Emission Vehicles, J. Air Waste Manage. Assoc., 44, 900-907 (1994). 

The solvent should not contain substances that contribute significantly to the production of photochemical smog and troposphere ozone. The volatile organic content of the product, as used, should not exceed 50 g/L. None of the components of the product will have a maximum incremental reactivity (MIR) exceeding 1.9 g Ofg of compound (the MIR for toluene). MIR values can be obtained from the maximum incremental reactivity list found in Appendix VII of the California Air Resources Board s California Exhaust Emission Standards and Test Procedures for 1988 and Subsequent Model Passenger Cars, Light-Duty Trucks and Medium-Duty Vehicles as amended on September 22, 1993. 

Carter WPL, Pierce JA, Luo D, Malkina IL (1995) Envirraunental chamber study of maximum incremental reactivities of volatile organic cranpounds. Atmos Environ 29(18) 2499—2511 POCP... 

Carter WPL (1997) Estimation of upper limit maximum incremental reactivities of VOCs. Report to California Air Resources Board Reactivity Research Advisory Committee, http // helium.ucr.edu/ carter/bycar1er.htm (POCP)... 

As a fourth step, discussion continues for the introduction of emission limits for other exhaust gas components, and for particulate matter of diesel powered vehicles. For example, there has been discussion in the USA and some European countries on separate - additional - emission limits for carbon dioxide, benzene and/or aldehydes. In the USA there is a project to consider an additional ozone-formation factor to be allocated to the tailpipe emission of passenger cars. This is because each exhaust gas component has a different potential to contribute to atmospheric ozone formation. This potential is quantified according to the theory of Carter by the maximum incremental reactivity (MIR) factor, expressed as grams of... 

Table 4. Maximum incremental reactivity factor for some selected exhaust gas components.

Maximum incremental reactivity factor (g ozone per g component)... 

The two large open circles on Figure 1 show the ROG and NOx levels chosen to serve as the base case in the incremental reactivity experiments that are currently underway in this chamber to assess ozone impacts of various different types of VOCs (Carter, 2004c). The 25-30 ppb NOx levels were chosen to be representative of pollution episodes of interest in California, based on input provided by the staff of the California Air Resources Board, which is funding most of the current reactivity studies. The ROG/NOx ratios were chosen to represent two sets of conditions of NOx availability relevant to VOC reactivity. The lower ROG/NOx ratio was chosen to represent the relatively higher NOx conditions of maximum incremental reactivity (MIR) where ozone is most sensitive to VOCs, to approximate the conditions used to derive the widely-used MIR ozone reactivity scale (Carter, 1994). The higher ROG/NOx ratio was chosen to be one-half that yielding maximum ozone levels, and is used to represent conditions where ozone is NOx-limited, but not so NOx-limited that VOC reactivity is irrelevant. These are referred to in the subsequent discussion as the MIR and MOIR/2 base eases, respeetively. 

Solvent Maximum Incremental Reactivity (grams ozone per gram of solvent)... 

This means to engender lower values of MIR (maximum incremental reactivity). 

The abbreviations for solvents used here are TCA for 1,1,1-trichloroethane, Freon for CFC-113, TCE for trichloroethylene, PCE for perchloroethylene, meth for methylene chloride, MEK for methyl ethyl ketone, and n-PB for n-propyl bromide. Other abbreviations used here are OTVD for open-top vapor degreaser, FISPs for Hansen Solubility Parameters, and MIR for Maximum Incremental Reactivity. Results of this approach are tabulated in Ref. 2, Appendix D1, Tables D1-11 through D1-15 (n-PB), D1-16(TCE), D1-18 (meth), D1-19 (PCE), and D1-20 (MEK). 

The order of the compounds determined by the magnitude of the mass emissions is not intended to reflect the relative influence of these compounds on atmospheric chemistry, greenhouse effect, or other atmospheric phenomena. To illustrate this point, compare in table I-C-5 the orders of importance of the top 31 species in mass emissions in table I-C-2 as estimated from a consideration of criteria other than mass emissions. We list the normalized relative values for molecular emissions (proportional to mass emissions/molecular weight), relative rate of attack by OH radicals (proportional to molecular emissions x oh), the relative rate of ozone generation as estimated for a polluted urban atmosphere (proportional to mass emissions x MIR, the maximum incremental reactivity factor Carter, 1998), and the relative number of CO2 molecules that atmospheric oxidation of this species will ultimately generate (proportional to molecular emissions x number of C-atoms molecule" ). The latter comparison... 

Carter, W.P.L. (1995) Computer modeling of environmental chamber measurements of maximum incremental reactivities of volatile organic compounds, Atmos. Env., 29, 2513-2527. 

Carter, W.P.L. (1998), Updated maximum incremental reactivity scale for regulation applications. Report to California Air Resources Board, Contract No. 95-308. 

TABLE 16.8 Typical Calculated Incremental Reactivities and Maximum Ozone as a Function of the VOC/NOx Ratio"... 

TABLE 5.6 Calculated Incremental Reactivities and Kinetic and Mechanistic Reactivities for CO and Selected VOCs for Maximum Ozone Formation Conditions, Based on Scenarios for 12 Urban Areas in the United States... 

The enhanced recovery of residual oil, which occurs as a consequence of wettability gradients in a reactive alkaline-acidic system, is illustrated in Figure 10. Incremental production in this tertiary flood begins about 0.6 PV after caustic injection and ends after injection of approximately 1.0 PV of caustic. This production is preceded by a pressure peak with a maximum which is two times the steady-state pressure drop of the secondary water-flood. The pressure drop maximum coincides with the concentration minimum of the hydroxyl ion species which elutes at the rear of the tertiary oil bank. 

With the normal control rod patterns required to maintain an acceptable power distribution in the operating core, an average control rod will be worth about 0.005 dk effective. The maximum worth of a rod in a typical power operation pattern will be about 0.01 dk effective. The notch increment dimensions and spacing of the rods are set to limit the reactivity insertion to about 0.0003 dk/k for any notch increment of control withdrawn. Preplanned withdrawal patterns and procedural patterns and procedural controls are used to prevent abnormal configurations yielding excessively high rod worth. 

The reactor will be pulsed with reactivity insertions from 1% to 1.4%(or the maximum available) in 0.1% increments. Calculate the transient rod fired position to obtain the desired reactivity insertions. One pulse will be fired for each reactivity step. A second pulse will be fired for one of the steps to provide an indication of the reproducibility of the measurements. The signal from the gamma ion chamber is sampled at one millisecond intervals and stored in the TestLab. The TestLab internal program calculates the information needed for the reactor log and records two channels of power-level data derived from the gamma-ray dose from the reactor core. The first channel, labeled "pulsetrace", records the full pulse. The second, labeled "pulserise", uses a smaller range and thus records the early part of the pulse most useful for reactor period measurements. In both cases the raw data is normalized such that the output is in MW. 

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