A comparison of measurements from ATMOS and instruments aboard the ER‐2 aircraft: Halogenated gases

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Abstract
We compare volume mixing ratio profiles of N2O, CFC‐11, CFC‐12, CCl4, SF6, and HCl in the mid‐latitude lower stratosphere measured by the ATMOS Fourier transform spectrometer on the ATLAS‐3 Space Shuttle Mission with in situ measurements acquired from the NASA ER‐2 aircraft during Nov 1994. Good agreement is found between ATMOS and in situ correlations of [CFC‐11], [CFC‐12], and [SF6] with [N2O]. ATMOS measurements of [CCl4] are 15% high compared to ER‐2 data, but agree within the systematic uncertainties. ATMOS observations of [HCl] vs [N2O] are within ∼10% of ER‐2 data for [HCl] > 1 ppbv, but exceed in situ measurements by larger fractional amounts for smaller [HCl]. ATMOS measurements of [ClONO2] agree well with values inferred from in situ observations of [ClO], [NO], and [O3]. The sum of [HCl] and [ClONO2] observed by ATMOS, supplemented by a minor contribution from [ClO] estimated with a photochemical model, is consistent with the levels of inorganic chlorine inferred from in situ measurements of chlorine source gases.

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