Open AccessMeasurements of NO x and PAN and estimates of O 3 production over the seasons during Mauna Loa Observatory Photochemistry Experiment 2
Author(s) -
Ridley B.,
Walega J.,
Hübler G.,
Montzka D.,
Atlas E.,
Hauglustaine D.,
Grahek F.,
Lind J.,
Campos T.,
Norton R.,
Greenberg J.,
Schauffler S.,
Oltmans S.,
Whittlestone S.
Publication year - 1998
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 - 10.1029/98jd00075
Subject(s) - peroxyacetyl nitrate , troposphere , atmospheric sciences , observatory , environmental science , altitude (triangle) , climatology , physics , geology , chemistry , mathematics , astrophysics , nox , geometry , organic chemistry , combustion
Measurements of peroxyacetyl nitrate (PAN) and NO x and a variety of other constituents were made over approximately 1‐month‐long intensives in the autumn of 1991 and the winter, spring, and summer of 1992 during the second Mauna Loa Observatory Photochemistry Experiment (MLOPEX 2). PAN and NO x in the free troposphere had maximum abundances in spring in concert with the well‐known maximum in O 3 . The ratio of the spring to summer averages was a factor of 4.1 for PAN, a factor of 1.6 for O 3 , and only a factor of 1.4 for NO x . During most intensives, variations over periods of a few days to a week were often larger than the average seasonal amplitude. In free tropospheric air masses local to Hawaii, average PAN/NO x ratios were a maximum in winter through spring but in the range of 0.25–0.86 in all intensives. PAN decomposition is unlikely to be the major net source of NO x in local air masses in summer and fall. The low HNO 3 /NO x ratios determined during MLOPEX 1 were confirmed during MLOPEX 2. Intensive average ratios of 1.6–3.8 over the year are lower than some model predictions. Both the low ratio and the magnitude of NO x imply a shortcoming in our understanding of the transformations and sources of NO y constituents in the central Pacific, The 3‐ to 4‐km altitude region near Hawaii was a net importer of O 3 , on average, over the year. The average net rate of production of O 3 in free tropospheric air was near zero in winter, −0.4 to −0.8 ppbv/d in spring, −1.4 ppbv/d in summer, and −0.6 ppbv/d in autumn. Thus the spring maximum in O 3 is not due to local photochemistry. We believe, as has been concluded from the long‐term measurements of long‐lived constituents by the Climate Monitoring and Diagnostics Laboratory, that the variation of ozone precursors over the year and on shorter timescales of a few days to a week is controlled predominantly by changes in long‐range transport: more frequent sampling of higher‐latitude and higher‐altitude air masses in winter and spring versus more frequent sampling of well‐aged air from lower altitudes and latitudes in summer and autumn.