A semi-Lagrangian view of ozone production tendency in North American outflow in the summers of 2009 and 2010 B. Zhang1, R. C. Owen1, J. A. Perlinger1, A. Kumar1, S. Wu1, M. Val Martin2, L. Kramer1, D. Helmig3, and R. E. Honrath1,† 1Atmospheric Sciences Program, Michigan Technological University, Houghton, MI, USA 2Department of Atmospheric Science, Colorado State University, Fort Collins, CO, USA 3Institute of Arctic and Alpine Research, University of Colorado, Boulder, CO, USA †Deceased
Abstract. The Pico Mountain Observatory, located at 2225 m a.s.l. in the Azores
Islands, was established in 2001 to observe long-range transport from North
America to the central North Atlantic. In previous research conducted at the
observatory, ozone enhancement (> 55 ppbv) in North American outflows was
observed, and efficient ozone production in these outflows was postulated.
This study is focused on determining the causes for high
d[O3] / d[CO] values (~1 ppbv ppbv−1) observed in the
summers of 2009 and 2010. The folded retroplume technique, developed by
Owen and Honrath (2009), was applied to combine upwind FLEXPART transport pathways
with GEOS-Chem chemical fields. The folded result provides a semi-Lagrangian
view of polluted North American outflow in terms of physical properties and
chemical processes, including production/loss rate of ozone and
NOx produced by lightning and thermal decomposition of peroxy acetyl nitrate (PAN). Two
transport events from North America were identified for detailed analysis.
High d[O3] / d[CO] was observed in both events, but due to differing
transport mechanisms, ozone production tendency differed between the two.
A layer of net ozone production was found at 2 km a.s.l. over the Azores in
the first event plume, apparently driven by PAN decomposition during
subsidence of air mass in the Azores–Bermuda High. In the second event, net
ozone loss occurred during transport in the lower free troposphere, yet
observed d[O3] / d[CO] was high. We estimate that in both events,
CO loss through oxidation contributed significantly to
d[O3] / d[CO] enhancement. Thus, it is not appropriate to use
CO as a passive tracer of pollution in these events. In general, use
of d[O3] / d[CO] as an indicator of net ozone
production/loss may be invalid for any situation in which oxidants are
elevated. Based on our analysis, use of d[O3] / d[CO] to diagnose
ozone enhancement without verifying the assumption of negligible CO loss is
Citation: Zhang, B., Owen, R. C., Perlinger, J. A., Kumar, A., Wu, S., Val Martin, M., Kramer, L., Helmig, D., and Honrath, R. E.: A semi-Lagrangian view of ozone production tendency in North American outflow in the summers of 2009 and 2010, Atmos. Chem. Phys., 14, 2267-2287, doi:10.5194/acp-14-2267-2014, 2014.