Case study for September 3, 1997-Eastern

US sulfate transport to Colorado Plateau

12 spatially coherent sites in TX, NM, AZ, CO 20% worst haze,with sulfate dominant

Table 1. SITE S percentile

(1997) S conc μg/m3 (adj to STP)

GRSA 98 0.69 MEVE 100 0.74 MOZI 98 0.47 ROMO 94 0.42 WEMI 100 0.62 BAND 100 0.75 GICL 99 1.18 BIBE 98 2.09 GUMO 98 1.71 TONT 100 1.11 CHIR 100 1.26 GRCA 100 0.74

Highest S for all 1997 at Arizona, New Mexico sites and Mesa Verde, 94-99 percentile other sites

2 days prior to event, flow was light from the east to southeast upwind of sites. Haze reported at many eastern US NWS stations

Weak cold front passes- stronger flow accelerates westward movement of hazy airmass? Flow in response to high pressure system along Canadian border

Bandalier, Big Bend 315 hour backtrajectories from noon local time Sep 3

BANDBIBE

TONT

Tonto, Grand Canyon 315 hour backtrajectories from noon local time Sep 3

Mt. Zirkel, Great Sand Dunes, 315 hour backtrajectories from noon local time Sep 3

MOZIGRSA

Conceptual model of event

• Highest S day for 1998 for Arizona and New Mexico sites long-range transport from eastern US

• Specific source areas in eastern US, unknown, could be large hazy blob and many source areas included from southeast to possibly Ohio River Valley

• Initial inspection of aerosol maps indicates rare to get this far west- but not unusual to reach Big Bend (from BRAVO study analyses)

• Movement of large early autumn high pressure west to east along Canadian border associated with this pattern and other cases of eastern US transport to Big Bend

• Additional analysis could look at airport visibility data, other aerosol data, additional cases (if found)

BAND, BIBE

GRCA