Paper in Press
JOURNAL OF GEOPHYSICAL RESEARCH, doi:10.1029/2012JD018738
Influence of Daily Variations in Baseline Ozone on Urban Air Quality in the United States Pacific Northwest
- We examine transport of baseline ozone between paired baseline and urban sites
- Baseline ozone explains 40-69% of daily variations in urban ozone mixing ratios
- In Boise, ID, baseline ozone alone may exceed US standards if they are tightened
We examine the influence of daily variations in baseline ozone (O<sub>3</sub>) on urban air quality in the United States (US) Pacific Northwest (PNW) during 2004-2010 through two analyses: (1) transport of free tropospheric (FT) O<sub>3</sub> from Mount Bachelor Observatory (MBO) to Boise, Idaho and (2) transport of marine boundary layer (MBL) O<sub>3</sub> from Cheeka Peak (CP) to Enumclaw, Washington. Both Boise and Enumclaw experience days with maximum daily eight-hour averages of O<sub>3</sub> (MDA8) exceeding US standards. Backward trajectory cluster analyses identify days when FT and MBL O<sub>3</sub> strongly influence MDA8 in Boise and Enumclaw. On these days, MBO and CP O<sub>3</sub> observations explain 40% and 69% of the variations in Boise and Enumclaw MDA8, respectively. Bivariate regressions for Boise/MBO and Enumclaw/CP have slopes of 0.52+/-0.16 and 1.04+/-0.08, respectively, representing the differing interplay of O<sub>3</sub> dilution, production and loss during FT to boundary layer transport (Boise/MBO) and fast boundary layer transport (Enumclaw/CP). AIRPACT-3/CMAQ high resolution air quality simulation results demonstrate how transport of O<sub>3</sub> from the FT above MBO contributes to elevated O<sub>3</sub> at Boise. Average MDA8 O<sub>3</sub> in Boise is higher than in Enumclaw due to site elevation and greater entrainment of FT air masses, a finding likely applicable to other PNW sites. Days with high baseline influence at Boise and Enumclaw have lower average MDA8 O<sub>3</sub> than other days; however, some of these days would still exceed the US standard if it is substantially tightened in 2013, highlighting the increasing importance of FT O<sub>3</sub> influence on urban MDA8.
Received 24 August 2012; accepted 26 November 2012.
Citation: (2012), Influence of Daily Variations in Baseline Ozone on Urban Air Quality in the United States Pacific Northwest, J. Geophys. Res., doi:10.1029/2012JD018738, in press.