Trace chemical measurements from the northern midlatitude lowermost stratosphere in early spring: Distributions, correlations, and fate

Abstract

In situ measurements of a large number of trace chemicals from the midlatitude (37–57°N) lower stratosphere were performed with the NASA DC‐8 aircraft during March 1994. Deepest penetrations into the stratosphere (550 ppb O 3 , 279 ppb N 2 O, and 350 K potential temperature) corresponded to a region that has been defined as the “lowermost stratosphere” (LS) by Holton et al. [1995]. Analysis of data shows that the mixing ratios of long‐lived tracer species (e. g. CH 4 , HNO 3 , NO y , CFCs) are linearly correlated with those of O 3 and N 2 O. A ΔNO y /ΔO 3 of 0.0054 ppb/ppb and ΔNO y /ΔN 2 O of −0.081 ppb/ppb is in good agreement with other reported measurements from the DC‐8. These slopes are however, somewhat steeper than those reported from the ER‐2 airborne studies. We find that the reactive nitrogen budget in the LS is largely balanced with HNO 3 accounting for 80% of NO y , and PAN and NO x together accounting for 5%. A number of oxygenated species (e. g. acetone, H 2 O 2 ) were present and may provide an important in situ source of HO x in the LS. SO 2 mixing ratios were found to increase in the stratosphere at a rate that was comparable to the decline in OCS levels. No evidence of particle formation could be observed. Ethane, propane, and acetylene mixing ratios declined rapidly in the LS with Cl atoms likely playing a key role in this process. A number of reactive hydrocarbons/halocarbons (e. g. C 6 H 6 , CH 3 I) were present at low but measurable concentrations.