Hydrocarbon Measurements Aboard the Ron Brown During NEAQS 2004: Chemical Time Scales and Evidence of Chlorine Chemistry in the Marine Boundary Layer

Ratios of the observed concentrations of Non-Methane Hydrocarbons (NMHCs) have frequently been used to gain insight into the loss mechanisms of those NMHCs. By choosing NMHCs with substantially different rates of reactions with a major reaction partner such as OH, together with an estimate of the OH mean concentration, a "chemical age" may be calculated for the air mass sampled. The ratio of toluene to benzene, for example, has been frequently invoked to calculate such a "chemical age". A different NMHC ratio, resulting in a substantially different calculated "chemical age", may be taken as evidence of more than one significant loss mechanism. Examples of such substantial disagreement will be presented using NMHCs that undergo rapid reaction with Cl radicals. The reconciliation of such disagreements yields an estimate of the marine boundary layer Cl concentration. This estimate will be compared to other reported indirect estimates of maritime Cl contentrations.