Ozone production in boreal fire smoke plumes using observations 3 from the Tropospheric Emission Spectrometer and the Ozone 4 Monitoring Instrument

9 [1] We examine the photochemical processes governing the production of ozone in 10 smoke from large Siberian fires that formed in July 2006 using colocated O3 and 11 CO profiles as measured by the Tropospheric Emission Spectrometer as well as NO2 and 12 aerosol optical depths as measured by the Ozone Monitoring Instrument. The Real-Time 13 Air Quality Model (RAQMS) is used to explain the observed variations of O3. Enhanced 14 levels of ozone up to 90 parts per billion (ppbv) are observed near and away from 15 the Siberian fires (60 N and 100 E) when sunlight and NOx are available. We also observe 16 significantly low O3 amounts (less then 30 ppbv) in the smoke plume from Siberian fires 17 in conjunction with optically thick aerosols. Despite this wide variance in observed ozone 18 values, the mean ozone value for all observations of the smoke plume is close to 19 background levels of approximately 55 ppbv in the free troposphere. Using RAQMS we 20 show that optically thick aerosols in the smoke plume can substantially reduce the 21 photochemical production of ozone and this can explain why the observed mean ozone 22 amount for all plume observations is not much larger than background values of 55 ppbv. 23 However, the anonymously low ozone amounts of 30 ppbv or less point toward other 24 unresolved processes that reduce ozone below background levels in the plume.