UC Davis

Aerosol and tropospheric ozone transport to North America has important implications for regional air quality and climate. We present data from Chews Ridge, a remote mountaintop site in California, in February–September 2012, which identifies separate Asian dust and Asian combustion aerosol signals and quantifies exogenous ozone. We use positive matrix factorization of size-fractionated aerosol X-ray fluorescence data and 206Pb/207Pb and 208Pb/207Pb isotope measurements to isolate aerosol signals of Asian origins and find good agreement between both types source attribution techniques. Power spectra of Asian dust and Asian combustion signals reveal two distinct peaks, one seasonal (~90 days) and one monthly (~25–30 days). Overall, 89% of the Asian dust signal occurs in March–May, compared with June–September, whereas only 51% of the Asian combustion signal occurs in March–May. Nearly half the Pb observed at Chews Ridge was derived from Asia (46%; 8.3% from Asian dust, 23% from Asian combustion, and 15% of the Asian Pb signal was not explained by the positive matrix factorization). A positive correlation between deseasonalized ozone concentrations and the Asian factors suggests that ozone is elevated by 6.3 ± 0.8 ppb due to transpacific transport. Scanning mobility particle size spectra were also measured from May to September and indicate that new particles are often produced and grow throughout the afternoon during onshore flow. We hypothesize that particle nucleation on the windward edge of the continent is an important source of new particles.