Open AccessHeterogeneous BrONO 2 hydrolysis: Effect on NO 2 columns and ozone at high latitudes in summer
Author(s) -
Randeniya L. K.,
Vohralik P. F.,
Plumb I. C.,
Ryan K. R.
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 - 10.1029/97jd01655
Subject(s) - ozone , aerosol , photodissociation , atmosphere (unit) , atmospheric sciences , latitude , stratosphere , daytime , atmospheric chemistry , chemistry , environmental science , meteorology , photochemistry , geology , physics , organic chemistry , geodesy
The heterogeneous reaction, N 2 O 5 + H 2 O aerosol → → 2HNO 3 , is responsible for increasing [HO x ] and repartitioning of active NO x into HNO 3 . Throughout much of the atmosphere, N 2 O 5 is formed predominantly at night owing to the rapid photolysis of its precursor, NO 3 , in sunlit hours. Laboratory measurements have shown that BrONO 2 + H 2 O aerosol → HOBr + HNO 3 (reaction (3)) also has the potential to cause repartitioning of ozone‐depleting species, although better determination of γ, the reaction probability, is still required for some stratospheric conditions. The diurnal behavior of N 2 O 5 and BrONO 2 are entirely different. In contrast to N 2 O 5 , BrONO 2 is formed predominantly during the daytime. The result of (3) is to increase [HOBr] at the expense of [BrONO 2 ]. Photolysis of HOBr then leads to increased [OH] and increased O 3 loss. In this work two‐dimensional calculations show clearly that the impact of (3) is greatest for high aerosol levels and for high latitudes in summer. The calculations have been used to determine the effects of increased aerosol loading on calculated NO 2 columns in the Antarctic during summer and autumn of 1990, 1991, 1992 and 1993. It is shown that (3) could be responsible for reductions in NO 2 columns during polar day comparable to those measured in 1992 and 1993 following the eruption of Mount Pinatubo. Reaction (3) results in only marginal changes to ozone catalytic loss cycles in 1990. However, for the high aerosol levels of 1992, the inclusion of this reaction results in up to 50% higher ozone loss rates in the 12 to 20 km range. This is caused predominantly by a large increase in [HO x ] tempered by a reduction in loss due to NO x . Calculations in which transport terms were switched off showed that, between 12 and 20 km at 77.5°N, local chemistry removes about 30% of the ozone between April and September compared with 20% when the effects of (3) are not included.