Environmental Chamber Studies of Atmospheric Reactivities of Volatile Organic Compounds, Effects of Varying ROG Surrogate and NOx
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Principal Investigator: William P. L. Carter
ARB Contract No. A032-096 (Full Report) ABSTRACT A series of indoor environmental chamber experiments were conducted to measure incremental reactivities of representative volatile organic compounds (VOCs) in irradiations of various reactive organic gas (ROG) surrogate - NOx - air mixtures designed to represent or approximate conditions of urban photochemical smog. Incremental reactivities are defined as the change in to ozone formation or OR radical levels caused by adding the VOC to a "base case" experiment, divided by the amount added. The base case included irradiations, at both relatively high and low NOx levels, of a surrogate mixture of B VOCs which model calculations predicted would yield the same results as use of a full ambient ROG mixture and high NOx experiments where ethylene alone represented the ambient ROGs. The test VOCs included carbon monoxide, n-butane, n-hexane, n-octane, ethylene, propene, ~-2-butene, benzene, toluene, m-xylene, formaldehyde, and acetaldehyde. The data obtained show that VOC have a greater range of incremental reactivities when simplified base case ROG surrogates are used than with the more realistic B-component surrogate. Reducing NOx reduced incremental reactivities by differing amounts for different VOCs, with ozone reactivities of propene, ~-2-butene, acetaldehyde, and the aromatics becoming negative in the low NOx experiments. These results are consistent with model predictions. The model simulated reactivities in experiments with the more complex surrogate reasonably well, though it was more variable in the simulations of the simpler systems, which are more sensitive to differences among the VOCs. Model calculations indicated that experimentally measured incremental reactivities may correlate well with those in the atmosphere under high NOx conditions, but not when NOx is low. Thus the best use for data from incremental reactivity experiments is evaluating the models used to predict reactivities in the atmosphere. |