Abstract
Abstract. In situ measurements of carbon monoxide (CO) and ozone (O3) at the Pico Mountain Observatory (PMO) located in the Azores, Portugal, are analyzed together with results from an atmospheric chemical transport model (GEOS-Chem) and satellite remote sensing data (AIRS (Atmospheric Infrared Sounder) for CO, and TES (Tropospheric Emission Spectrometer) for O3) to examine the evolution of free-troposphere CO and O3 over the North Atlantic for 2001–2011. GEOS-Chem captured the seasonal cycles for CO and O3 well but significantly underestimated the mixing ratios of CO, particularly in spring. Statistically significant (using a significance level of 0.05) decreasing trends were found for both CO and O3 based on harmonic regression analysis of the measurement data. The best estimates of the possible trends for CO and O3 measurements are −0.31 ± 0.30 (2-σ) ppbv yr−1 and −0.21 ± 0.11 (2-σ) ppbv yr−1, respectively. Similar decreasing trends for both species were obtained with GEOS-Chem simulation results. The most important factor contributing to the decreases in CO and O3 at PMO over the past decade is the decline in anthropogenic emissions from North America, which more than compensate for the impacts from increasing Asian emissions. It is likely that climate change in the past decade has also affected the intercontinental transport of O3.
Highlights
Carbon monoxide (CO) and ozone (O3) are important atmospheric pollutants in the troposphere
Contribution of fossil fuel emissions in Asia shows a statistically significant (p value < 0.001) increase. These results indicate that reductions in CO from North America and Europe could be the primary reasons for the possible decrease in CO at Pico Mountain Observatory (PMO), which outweigh the effects of increasing CO from Asia in the past decade
The Goddard Earth Observing System (GEOS)-Chem model performance is evaluated by comparing simulation results against measurements at PMO and satellite observations
Summary
Carbon monoxide (CO) and ozone (O3) are important atmospheric pollutants in the troposphere. The atmospheric lifetime of CO ranges from weeks to months (Duncan et al, 2007), and the lifetime for O3 varies from days to months in the troposphere (Law, 2010; Wang et al, 1998) These relatively long lifetimes enable these species to undergo intercontinental transport. US sources account for approximately 80 % of anthropogenic emissions from North America (Wang et al, 2009) These changes in emissions are expected to influence the freetroposphere CO and O3 concentrations over the North Atlantic. We combine 10-year in situ measurements of CO and O3 at this station with results from a chemical transport model (the GEOS-Chem chemical transport model) as well as satellite data to examine the seasonal variation and long-term trends in free-tropospheric CO and O3 over the North Atlantic for the past decade
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