Abstract
We use the GEOS‐Chem chemical transport model and its adjoint to quantify source contributions to ozone pollution at two adjacent sites on the U.S. west coast in spring 2006: Mt. Bachelor Observatory (MBO) at 2.7 km altitude and Trinidad Head (TH) at sea level. The adjoint computes the sensitivity of ozone concentrations at the receptor sites to ozone production rates at 2° × 2.5° resolution over the history of air parcels reaching the site. MBO experiences distinct Asian ozone pollution episodes; most of the ozone production in these episodes takes place over East Asia with maxima over northeast China and southern Japan, adding to a diffuse background production distributed over the extratropical northern hemisphere. TH shows the same Asian origins for ozone as MBO but no distinct Asian pollution episodes. We find that transpacific pollution plumes transported in the free troposphere are diluted by a factor of 3 when entrained into the boundary layer, explaining why these plumes are undetectable in U.S. surface air.
Highlights
[1] We use the Goddard Earth Observing System (GEOS)-Chem chemical transport model and its adjoint to quantify source contributions to ozone pollution at two adjacent sites on the U.S west coast in spring 2006: Mt
Ozone is produced in the troposphere by photochemical oxidation of CO and volatile organic compounds (VOCs) in the presence of nitrogen oxides (NOx NO + NO2)
[11] Figure 2 shows the sensitivities of ozone concentrations at Mt. Bachelor Observatory (MBO) and Trinidad Head (TH) to the global distribution of ozone production rates for the previous two months, as inferred from the GEOS-Chem model adjoint
Summary
[1] We use the GEOS-Chem chemical transport model and its adjoint to quantify source contributions to ozone pollution at two adjacent sites on the U.S west coast in spring 2006: Mt. [4] We use here the GEOS-Chem CTM and its adjoint to estimate source contributions to surface ozone pollution in spring 2006 at two nearby sites on the U.S west coast, one at high altitude (Mt. Bachelor Observatory, Oregon) and one at sea level (Trinidad Head, California).
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