Influence of long‐range‐transported pollution on the annual and diurnal cycles of carbon monoxide and ozone at Cheeka Peak Observatory

Abstract

[1] We assess the importance of distant pollution sources on the marine background by combining measurements of carbon monoxide (CO) and ozone (O 3 ) with model simulations from the GEOS-CHEM chemical transport model and two types of back trajectories. Measurements were made over a complete annual cycle from March 2001 to May 2002 at Cheeka Peak Observatory (CPO) in Washington State. Data from an earlier campaign (March-April 1997 and1998) were also incorporated. The seasonal cycles of CO and O 3 show a spring maximum and a summer minimum, consistent with other remote sites in the marine boundary layer. European and Asian pollution emission sources of CO, parameterized by GEOS-CHEM, were grouped into one category called ''LRT,'' representing ''long-range transport.'' LRT values produced good correlations with measured CO (monthly averaged r = 0.60, 6-hour averages) and were found to comprise between 15 and 60% of total CO, with higher values in winter/spring and lower values in the summer/fall. CO and O 3 observations were classified on the basis of these LRT values, creating two general categories: ''more polluted'' (LRT > 75th percentile from monthly distribution) and ''less polluted'' (LRT < 25th percentile). The difference between these two categories is a measure of the net Asian enhancement above the background and reaches a maximum in the spring of 30-ppbv CO and in the spring-fall of 7-ppbv O 3 . The Asian O 3 enhancement peaked at an average of 4 ppbv from April to October, which is the time of year of greatest urban air quality concerns in North America. Numerous long-range transport ''events'' (defined by at least 24 continuous hours of LRT > 75% percentile) were observed throughout the year. Ozone behavior was quite complicated during these events, producing no consistent enhancements. Classification of the measurements with LRT values from GEOS-CHEM is compared to back trajectories, both isentropic and kinematic. Isentropic trajectories agree reasonably well with GEOS-CHEM between February and May in capturing the CO enhancements in air masses influenced by recent emissions but were found to be less useful from June to January. HYSPLIT kinematic trajectories were slightly better at capturing the Asian pollution events than isentropic trajectories but still missed an event during the summer completely that was verified by GEOS-CHEM. Possible reasons for poor trajectory performance in the summer and fall are discussed. Long-range transport appears not to affect the magnitude of the diurnal variability of O 3 measurements at CPO, which reflect daytime production of 2-4 ppbv/d. Rather, ship traffic in the vicinity of CPO, which supplies NO x through combustion, likely plays a dominant role.

Transpacific and regional atmospheric transport of anthropogenic semivolatile organic compounds to Cheeka Peak Observatory during the spring of 2002

“…During this sampling campaign, CPO was influenced by Asian pollution during our 15–16 March, 27–28 March, and 22–23 April 2002 sampling periods. This was determined from CPO observations of CO and aerosols [ Weiss‐Penzias et al , 2004], from the GEOS‐CHEM global model [ Liang et al , 2004], and suggested by our PCA results and trajectory classification. The 48‐hour sample of 15 March 2002 overlapped with the first transpacific event.…”

“…This sampling period was also the only time triallate, endosulfan II, and endosulfan sulfate were detected. The presence of elevated concentrations of PAHs and pesticides (including the detection of pesticides not measured in other samples), changes in the normalized concentrations of PAHs and pesticides shown by PCA in section 3.5, back trajectories that pass over Asia, and the GEOS‐CHEM model predictions, suggest Europe and Asia as potential sources of these SOCs on 15–16 March, 27–28 March, and 22–23 April 2002 [ Weiss‐Penzias et al , 2004; Liang et al , 2004]. The estimated atmospheric half‐lives for the measured pesticides in the gas‐phase range from 2.2 days (cis‐nonachlor and trans‐nonachlor) to 1731 days (chlorothalonil) (EPI Suite v. 3.1.1, Environmental Protection Agency, 2003).…”

“…During the spring of 2002, as part of the Intercontinental Transport and Chemical Transformation 2002 (ITCT 2K2) campaign and the Photochemical Ozone Budget of the Eastern North Pacific Atmosphere (PHOBEA2) experiment [ Bertschi et al , 2004; Liang et al , 2004; D. D. Parrish et al, ITCT‐2K2 research initiative overview, submitted to Journal of Geophysical Research , 2004; Weiss‐Penzias et al , 2004], high‐volume (hi‐vol) air samples were collected at Cheeka Peak Observatory (CPO) in Washington State and analyzed for a wide range of anthropogenic SOCs, including PAHs and pesticides. These were some of the first measurements of these anthropogenic SOCs at a remote site in the Pacific Northwest of the United States.…”

Global estimates of CO sources with high resolution by adjoint inversion of multiple satellite datasets (MOPITT, AIRS, SCIAMACHY, TES)

“…A number of satellite instruments have been measuring tropospheric CO globally over the past decade including MOPITT (2000-) (Edwards Published by Copernicus Publications on behalf of the European Geosciences Union. et al, 2006b;Emmons et al, 2007), SCIAMACHY (2002 (Bovensmann et al, 1999;Buchwitz et al, 2007;Burrows et al, 1995;de Laat et al, 2007), AIRS (2002-) (McMillan et al, 2005Warner et al, 2007;Yurganov et al, 2008), ACE-FTS (2003-) (Clerbaux et al, 2005, TES (2004-) (Lopez et al, 2008;Luo et al, 2007a;Rinsland et al, 2006), andIASI (2007-) (FortemsCheiney et al, 2009;Turquety et al, 2009). These satellite data expand the perspective offered by in situ observations, such as from the NOAA/GMD surface monitoring network (Novelli et al, 2003) and from commercial aircraft (Nedelec et al, 2003).…”

European CO budget and links with synoptic circulation based on GEOS-CHEM model simulations

“…Due to the CO lifetime in the troposphere (30Á90 d), the pollutant can be transported in continental scales through several pathways (Holloway et al, 2000;Li et al, 2002;Liu et al, 2003;Duncan and Bey, 2004;Huntrieser and Schlager, 2004;Liang et al, 2004;Weiss-Penzias et al, 2004;Auvray and Bey, 2005;Drori et al, 2012). The transatlantic long-range transport (LRT) is particularly *Corresponding author.…”