Orographic:

Relating to the physical geography of mountains and mountain ranges

PAN:

Peroxyacetyl nitrate

PBL:

Planetary boundary layer

PM:

Particulate matter

PM2.5:

Particulate matter having an aerodynamic diameter of 2.5 µm or less

PM10:

Particulate matter having an aerodynamic diameter of 10 µm or less

ppb:

Parts per billion by volume

ppm:

Parts per million by volume

Precision:

Agreement among individual measurements of the same property, under prescribed similar conditions

S:

Sulfur

SIP:

State implementation plans for NAAQS

Sulfuric acid:

H₂SO₄

Synoptic:

Of or relating to data obtained nearly simultaneously over a large area of the atmosphere

Tg:

Teragram, 1 x 10¹² g

TSP:

Total suspended particulates

Uncertainty:

The degree of confidence that can be assigned to a numerical measurement in terms of both its accuracy and its precision

USDA:

U.S. Department of Agriculture

VOC:

Volatile organic compound

Volatile solids:

Weight lost upon ignition at 550 °C (using Method 2540 E of the American Public Health Association). Volatile solids provide an approximation of moisture and organic matter present.

yr:

year(s)