Modeling the chemistry during TOPSE low ozone events Mathew Evans, D. Jacob, Mathew Evans, D. Jacobs, C. Cantrell, F. Eisele, F. Flocke, A. Fried, B. Ridley, B Heikes, D Blake, R Talbot + many other from TOPSE and Harvard mje@io.harvard.edu

Ozone depletion events Various levels of depletion (20 to 0.1 ppbv) In boundary layer

Bromine chemistry • Source of bromine? Sea salt / snow • Recycling through aerosols • Interaction between BrOx and HOx and BrOx and NOx

TOPSE data Features • NOx minimum at 10 ppbv of O3 • PAN increases with lower O3 • Hydrocarbons drop with O3, ethyne linearly, ethane curved North of 55N, Below 500m, 11-13 hr local

TOPSE data Features • Radicals drop of with lower O3 • BrO maximum at higher O3 • Range of O3 a SBr concentration

Box Model

Initial comparison Features • Not enough O3 loss • NOx drops too low • No increase in PAN • Hydrocarbons seen reasonable

Initial comparison Features • Radicals concentrations seem reasonable • BrO concentrations seem reasonable • Model seems to have less efficient O3 loss, or some loss of Br from system

NO3- + 2Br- + 3H+ -> Br2 + HNO2 + H2O Problems? Solution? • Not enough O3 destruction • Too much NOx loss • Solution? NO3- + 2Br- + 3H+ -> Br2 + HNO2 + H2O Lengyel, Nagy, Bazsa, Kinetic study of the autocatalytic nitric acid - bromide reaction and its reverse the nitrous acid-bromine reaction J. Phys. Chem., 1989, 2801-2807

Updated comparison Features • NOx concentration better • PAN increases but not much (CH3CHO?) • Hydrocarbon decay good

Updated comparison Features • OH concentration seems high • RO2 concentration good • Too little BrO? • Too much SBr?

What changes with NOx? Standard With bromine

What happens to HOx? Standard With bromine

Conclusions Simple model reproduces features of the TOPSE data Agreement improves with extra reaction to convert NO3- to NOx. Model seems to underestimate efficiency of O3 loss with respect to SBr. PAN chemistry may relate to CH3CHO from snow pack.