The weathering of volatile hydrocarbons from crude oil slicks on water

Abstract

Comparing total C (1) to C (10) hydrocarbons measured in water column samples immediately after chemical dispersion of crude oil slicks in field studies with those found in chemical dispersion of fresh crude oil showed complete loss of these hydrocarbons from the field slicks in less than two hours. This independent method of measuring evaporation showed more rapid evaporation than found in most other field studies that collected samples of oil from the slick. The easiest part of the slick to sample is the thicker portion, which may be remnants that are less weathered than the slick as a whole. Many laboratory-weathering studies have used slick thickness many times greater than in the field with evaporation occurring in days rather than hours. Some evaporation models can quickly and inexpensively predict volatile hydrocarbon loss under different wind conditions, and varying air and water temperatures. The rapid loss of C (1) to C (10) hydrocarbons reduces biological toxicity, and restricts possible adverse effects to areas near the spill site. Evaporation of these hydrocarbons likewise increases slick oil viscosities and reduces chemical dispersant effectiveness. Thus the best slick control is obtained if it is sprayed quickly, although some oils can be effectively treated for several days.