Vertical profiles of O3, aerosols, CO and NMHCs in the Northeast Pacific during the TRACE-P and ACE-ASIA experiments

Abstract

Airborne observations of NMHCs, O3, CO, and aerosol scatter were made near the coast of Washington State from 29 March to 6 May 2001 as part of the Photochemical Ozone Budget of the Eastern North Pacific-II (PHOBEA-II) experiment. These observations overlapped the time period of the TRACE-P (24 February to 10 April 2001) and ACE-ASIA (27 March to 30 April 2001) experiments operating in the Western Pacific. Measurements were made during 12 flights at 48.31 ± 0.03°N latitude, 124.63 ± 0.08°W longitude at altitudes from 0 to 6 km. On several flights, significant enhancements in all species were observed and are attributed to transport from the Eurasian continent, including a long-range transport event observed on 14 April 2001. This event contained substantial CO, NMHC, and aerosol loadings and was identified by the Total Ozone Mapping Spectrometer (TOMS) aboard the Earth Probe Satellite and airborne and surface measurements throughout North America. This airmass was unique in that it contained the highest levels of aerosol scatter, CO, and various NMHCs observed in 2001, was the only flight with a low Ångstrom coefficient (0.7) indicating dominance of super micron aerosols, and had a negative relationship between ozone and aerosol scatter (r = -0.30). Within this mineral dust and pollution layer, aerosol scatter, propane, and CO were enhanced by 1054%, 85%, and 36%, respectively, over the observed spring 2001 median values between 3.5 and 6 km. A comparison of our previous aircraft campaign in 1999 with 2001 observations shows that ozone, aerosol scatter, and most NMHCs were significantly lower in the spring of 2001. The exact cause is still under investigation, but the combination of elevated ozone, aerosol scatter, and NMHCs suggests a combustion source that was enhanced and/or transported more efficiently during the spring of 1999.