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Papers by Christine Maddox

Environmental Science & Technology, 2016

Experiments were conducted at the California Air Resources Board Haagen-Smit Laboratory to unders... more Experiments were conducted at the California Air Resources Board Haagen-Smit Laboratory to understand changes in vehicle emissions in response to stricter emissions standards over the past 25 years. Measurements included a wide range of volatile organic compounds (VOCs) for a wide range of spark ignition gasoline vehicles meeting varying levels of emissions standards, including all certifications from Tier 0 up to Partial Zero Emission Vehicle. Standard gas chromatography (GC) and high performance liquid chromatography (HLPC) analyses were employed for drive-cycle phase emissions. A proton-transfer-reaction mass spectrometer measured time-resolved emissions for a wide range of VOCs. Cold-start emissions occur almost entirely in the first 30-60 s for newer vehicles. Cold-start emissions have compositions that are not significantly different across all vehicles tested and are markedly different from neat fuel. Hot-stabilized emissions have varying importance depending on species and may require a driving distance of 200 miles to equal the emissions from a single cold start. Average commute distances in the U.S. suggest the majority of in-use vehicles have emissions dominated by cold starts. The distribution of vehicle ages in the U.S. suggests that within several years only a few percent of vehicles will have significant driving emissions compared to cold-start emissions.

Environ Sci Technol, 2005

Resources Board, El Monte, California 91731 without the vehicle running) were measured throughout... more Resources Board, El Monte, California 91731 without the vehicle running) were measured throughout this study and were helpful in determining the incremental increase in pollutant emissions. Also, the on-site determination of VOCs, especially 1,3-butadiene, helped minimize measurement losses due to sample degradation after collection.

Exhaust from vehicles powered by reformulated gasoline and methanol/gasoline blends has been anal... more Exhaust from vehicles powered by reformulated gasoline and methanol/gasoline blends has been analyzed by FTIR spectroscopy in parallel with conventional techniques. Linear regression analysis of the data showed the following relationships between the FTIR and conventional measurements: methane (0.89X + 0.31, R2 equals 0.96), carbon monoxide (0.82X + 34, R2 equals 0.96), formaldehyde (0.84X + 0.003, R2 equals 0.97), methanol (0.72X + 4.0, R2 equals 0.86), nitric oxide (0.93X + 0.83, R2 equals 0.89), and total non- methane hydrocarbons (1.02X + 2.8, R2 equals 0.96), where the slope, intercept (ppm) and correlation coefficient are shown in parenthesis. With the exception of methanol, good linear correlations are indicated. The apparent non-linearity for methanol is most likely due to the coaddition of interferograms during large concentration transients. Although the validity of FTIR measurements must be assessed on a compound-by-compound basis, the results of this study indicate that valid measurements of motor vehicle exhaust components can be made with non specialized (non-real-time) FTIR instruments.

Measurement of Atmospheric Gases, 1991

ABSTRACT Exhaust from vehicles powered by reformulated gasoline and methanol/gasoline blends has ... more ABSTRACT Exhaust from vehicles powered by reformulated gasoline and methanol/gasoline blends has been analyzed by FTIR spectroscopy in parallel with conventional techniques. Linear regression analysis of the data showed the following relationships between the FTIR and conventional measurements: methane (0.89X + 0.31, R2 equals 0.96), carbon monoxide (0.82X + 34, R2 equals 0.96), formaldehyde (0.84X + 0.003, R2 equals 0.97), methanol (0.72X + 4.0, R2 equals 0.86), nitric oxide (0.93X + 0.83, R2 equals 0.89), and total non- methane hydrocarbons (1.02X + 2.8, R2 equals 0.96), where the slope, intercept (ppm) and correlation coefficient are shown in parenthesis. With the exception of methanol, good linear correlations are indicated. The apparent non-linearity for methanol is most likely due to the coaddition of interferograms during large concentration transients. Although the validity of FTIR measurements must be assessed on a compound-by-compound basis, the results of this study indicate that valid measurements of motor vehicle exhaust components can be made with non specialized (non-real-time) FTIR instruments.

SAE Technical Paper Series, 1995

Vehicle exhaust emissions measurements are reported for full-size panel vans operating on four al... more Vehicle exhaust emissions measurements are reported for full-size panel vans operating on four alternative motor fuels and control gasoline. The emissions tests produced data on in-use vans. The vans were taken directly from commercial delivery service for testing as they ...

Environmental Science & Technology, 2005

Environmental Science & Technology, 2013

Dilution and smog chamber experiments were performed to characterize the primary emissions and se... more Dilution and smog chamber experiments were performed to characterize the primary emissions and secondary organic aerosol (SOA) formation from gasoline and diesel small off-road engines (SOREs). These engines are high emitters of primary gas- and particle-phase pollutants relative to their fuel consumption. Two- and 4-stroke gasoline SOREs emit much more (up to 3 orders of magnitude more) nonmethane organic gases (NMOGs), primary PM and organic carbon than newer on-road gasoline vehicles (per kg of fuel burned). The primary emissions from a diesel transportation refrigeration unit were similar to those of older, uncontrolled diesel engines used in on-road vehicles (e.g., premodel year 2007 heavy-duty diesel trucks). Two-strokes emitted the largest fractional (and absolute) amount of SOA precursors compared to diesel and 4-stroke gasoline SOREs; however, 35-80% of the NMOG emissions from the engines could not be speciated using traditional gas chromatography or high-performance liquid chromatography. After 3 h of photo-oxidation in a smog chamber, dilute emissions from both 2- and 4-stroke gasoline SOREs produced large amounts of semivolatile SOA. The effective SOA yield (defined as the ratio of SOA mass to estimated mass of reacted precursors) was 2-4% for 2- and 4-stroke SOREs, which is comparable to yields from dilute exhaust from older passenger cars and unburned gasoline. This suggests that much of the SOA production was due to unburned fuel and/or lubrication oil. The total PM contribution of different mobile source categories to the ambient PM burden was calculated by combining primary emission, SOA production and fuel consumption data. Relative to their fuel consumption, SOREs are disproportionately high total PM sources; however, the vastly greater fuel consumption of on-road vehicles renders them (on-road vehicles) the dominant mobile source of ambient PM in the Los Angeles area.