Open AccessEvidence of heterogeneous chemistry on sulfate aerosols in stratospherically influenced air masses sampled during PEM‐West B
Author(s) -
Kotamarthi V. R.,
Rodriguez J. M.,
Sze N. D.,
Kondo Y.,
Pueschel R.,
Ferry G.,
Bradshaw J.,
Sandholm S.,
Gregory G.,
Davis D.,
Liu S.
Publication year - 1997
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/97jd02511
Subject(s) - troposphere , stratosphere , atmospheric sciences , tropopause , altitude (triangle) , atmospheric chemistry , sulfate , nitrogen , reactive nitrogen , aerosol , air mass (solar energy) , environmental science , bromine , chemistry , meteorology , ozone , physics , geometry , mathematics , organic chemistry , boundary layer , thermodynamics
Signatures of the N 2 O 5 hydrolysis by sulfate aerosols have been previously documented, primarily from balloon and remote‐sensing platforms, by measurements of nitrogen species aboard the NASA ER‐2 flying at an altitude of approximately 20 km and some ER‐2 and DC‐8 measurements near the tropopause during stratospheric campaigns. This study documents such signatures in the NO x /NO y ratios derived from DC‐8 measurements during Pacific Exploratory Measurements in the Western Pacific Ocean (PEM‐West B) in stratospherically influenced air masses sampled during a level leg at an altitude of 10.7 km in flight 17 out of Japan. Despite the very low abundance of total bromine, we also show that heterogeneous hydrolysis of BrNO 3 on sulphate aerosols can catalytically convert NO x and liquid H 2 O into HNO 3 and OH and thereby lower the calculated equilibrium NO x /NO y by about 20 to 35% in these air masses, bringing closer agreement with the nitrogen partitioning deduced from measurements. However, the NO x /NO y ratios calculated from a model including heterogeneous chemistry were a factor of 3 smaller than ratios derived from data for a segment of this flight leg when DC‐8 measurements indicated a stronger tropospheric influence. We also modeled the equilibrium partitioning of nitrogen species for all upper tropospheric air masses encountered by the DC‐8; since NO y in the troposphere may contain nonnegligible contributions from long‐lived nitrates (such as peroxyacetylnitrate), we have compared instead modeled and measured NO x /HNO 3 . The calculated equilibrium NO x /HNO 3 ratios using only gas‐phase chemistry are on the average smaller than those deduced from measurements in upper tropospheric air masses; inclusion of N 2 O 5 hydrolysis reduces these ratios by an additional 20%, thus worsening the discrepancy. These results suggest a rapid transition from “denoxified” conditions in the lower stratosphere to “renoxified” conditions in the upper troposphere. This transition could be due to intrinsically different chemistry in the troposphere. Alternatively, rapid transport in the troposphere could keep the NO x and HNO 3 away from chemical equilibrium. Detailed analysis of current and future tropospheric data could shed light on this issue.