Time series of BCt and COt surface concentrations
over the northeast and midwest in summer show greater
autocorrelation in the future than for present-day. We
counted the number of consecutive days with regional
concentrations above the 84th percentile as representative
of pollution episodes. Over the midwest we found an
increase of episode duration from 2.3 days to 3.0 days for
COt and from 2.4 days to 4.6 days for BCt. In the northeast,
COt pollution episodes lengthen from 2 to 2.5 days, but the
change for BCt episodes is negligible.