Radical loss in the atmosphere from Cu-Fe redox coupling in aerosols 1Program in Atmospheric and Oceanic Sciences, Princeton University, Princeton, NJ 08542, USA
16 Jan 2013
2Geophysical Fluid Dynamics Laboratory/National Oceanic and Atmospheric Administration, Princeton, NJ 08542, USA
3School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
Received: 21 September 2012 – Published in Atmos. Chem. Phys. Discuss.: 15 October 2012 Abstract. The hydroperoxyl radical (HO2) is a major precursor of OH and
tropospheric ozone. OH is the main atmospheric oxidant, while tropospheric
ozone is an important surface pollutant and greenhouse gas. Standard
gas-phase models for atmospheric chemistry tend to overestimate observed
HO2 concentrations, and this has been tentatively attributed to
heterogeneous uptake by aerosol particles. It is generally assumed that
HO2 uptake by aerosol involves conversion to H2O2, but this
is of limited efficacy as an HO2 sink because H2O2 can
photolyze to regenerate OH and from there HO2. Joint atmospheric
observations of HO2 and H2O2 suggest that HO2 uptake by
aerosols may in fact not produce H2O2. Here we propose a catalytic
mechanism involving coupling of the transition metal ions Cu(I)/Cu(II) and
Fe(II)/Fe(III) to rapidly convert HO2 to H2O in aqueous aerosols.
The implied HO2 uptake and conversion to H2O significantly affects
global model predictions of tropospheric OH, ozone, carbon monoxide (CO) and
other species, improving comparisons to observations in the GEOS-Chem model.
It represents a previously unrecognized positive radiative forcing of
aerosols through the effects on the chemical budgets of major greenhouse
gases including methane and hydrofluorocarbons (HFCs).
Revised: 10 January 2013 – Accepted: 11 January 2013 – Published: 16 January 2013
Citation: Mao, J., Fan, S., Jacob, D. J., and Travis, K. R.: Radical loss in the atmosphere from Cu-Fe redox coupling in aerosols, Atmos. Chem. Phys., 13, 509-519, doi:10.5194/acp-13-509-2013, 2013.