Worst 20% Hazes Across the Country

Based on IMPROVE Speciation Data

by Marc Pitchford

August 2001

What Causes Worst Day & When do the Occur

• Southeastern US– Sulfate dominates worst case days– Most worst case days are in the late summer,

rare to have any during cold periods

• Northeastern US– Sulfates dominate with occasional high nitrate– Many worst days are in the summer, but every

season has some worst days

What Causes Worst Day & When do the Occur

• Northern Tier – Sulfates contribute any time of year– Nitrates contribute primarily in the Winter– Organics are occasionally important in the

Summer

What Causes Worst Day & When do the Occur

• Interior Western US– Sulfates, Organics, & Coarse Mass share the

blame on most worst case days– Apparent fire emissions (very high organic &

elemental carbon) are sporadically responsible for unusually high haze levels

– Apparent dust storms (very high coarse mass & fine soil) are occasionally responsible for unusually high haze levels

What Causes Worst Day & When do the Occur

• California – Nitrate, sulfate, & organic species contribute

most on worst days– Worst days are distributed throughout the year

What Causes Worst Day & When do the Occur

• Alaska– Sulfate is important especially in the cold

seasons (arctic haze from Eurasia?)– Organic is important especially in the warm

seasons (apparently from forest fires)