[1] The distribution and atmospheric budgets for molecular hydrogen and its deuterium component dD are simulated with the GEOS-Chem global chemical transport model and constrained by observations of H 2 from the NOAA Climate Monitoring and Diagnostics Laboratory network and dD observations from ship and ground stations. Our simulation includes a primary H 2 source of 38.8 Tg a À1 (22.7 Tg a À1 from fossil and biofuels, 10.1 Tg a À1 from biomass burning, 6.0 Tg a À1 from the ocean) (where a is years) and a secondary photochemical source from photolysis of formaldehyde of 34.3 Tg a À1 . The simulated global tropospheric mean H 2 is 525 ppbv, with a tropospheric burden of 141 Tg and tropospheric lifetime of 1.9 a. Uptake by enzymes in soils accounts for 75% of the H 2 sink, with the remainder due to reaction with OH. The model captures the observed latitudinal, vertical, and seasonal variations of H 2 . For dD we find that a photochemical source signature from methane and biogenic volatile organic compound oxidation of 162% yields a global mean atmospheric dD of 130%, consistent with atmospheric observations. The model captures the observed latitudinal gradient in dD, simulating a 21% greater enrichment in the Southern Hemisphere because of the predominance of isotopically depleted fossil fuel emissions in the Northern Hemisphere. We find that stratospheric-tropospheric exchange results in 37% enrichment of tropospheric dD. Our simulation provides new simultaneous constraints on the H 2 soil sink (55 ± 8 Tg a À1 ), the ocean source (6 ± 3 Tg a À1 ), and the isotopic signature for photochemical production (162 ± 57%).Citation: Price, H., L. Jaeglé, A. Rice, P. Quay, P. C. Novelli, and R. Gammon (2007), Global budget of molecular hydrogen and its deuterium content: Constraints from ground station, cruise, and aircraft observations,

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Using a 15‐year record of O3 from Lassen Volcanic National Park, a rural elevated site in northern California, data from two aircraft campaigns conducted in 1984 and 2002 over the eastern North Pacific, and observations spanning 18 years from five U.S. west coast, marine boundary layer sites, we show that O3 in air arriving from the Eastern Pacific in spring has increased by approximately 10 ppbv, i.e. 30% from the mid 1980s to the present. This positive trend in O3 correlates with the increasing trend in global nitrogen oxide emissions, which is especially pronounced in Asia. As spring is the season of strongest transport of Asian emissions to the Pacific, we conclude that the emission trend is the most likely cause of the O3 trend.

[1] Measurements during the Intercontinental Transport and Chemical Transformation 2002 (ITCT 2K2) field study characterized the springtime, eastern Pacific ozone distribution at two ground sites, from the National Oceanic and Atmospheric Administration WP-3D aircraft, and from a light aircraft operated by the University of Washington. D. Jaffe and colleagues compared the 2002 ozone distribution with measurements made in the region over the two previous decades and show that average ozone levels over the eastern midlatitude Pacific have systematically increased by $10 ppbv in the last two decades. Here we provide substantial evidence that a marked change in the photochemical environment in the springtime troposphere of the North Pacific is responsible for this increased O 3 . This change is evidenced in the eastern North Pacific ITCT 2K2 study region by (1) larger increases in the minimum observed ozone levels compared to more modest increases in the maximum levels, (2) increased peroxyacetyl nitrate (PAN) levels that parallel trends in NO x emissions, and (3) decreased efficiency of photochemical O 3 destruction, i.e., less negative O 3 photochemical tendency (or net rate of O 3 photochemical production; P(O 3 )). This changed photochemical environment is hypothesized to be due to anthropogenic emissions from Asia, which are believed to have substantially increased over the two decades preceding the study. We propose that their influence has changed the springtime Pacific tropospheric photochemistry from predominately ozone destroying to more nearly ozone producing. However, chemical transport model calculations indicate the possible influence of a confounding factor; unusual transport of tropical air to the western North Pacific during one early field study may have played a role in this apparent change in the photochemistry.