Definitions for "Secondary standard"
A secondary standard reference card is a calibration card of known signal amplitude at saturation that is traceable to the primary and master standards. See RM7811-2 and RM7811-6.
An air-quality standard designed to protect human welfare (property, vegetation, etc.) as opposed to health.
"Secondary ambient air quality standards" or "secondary standards" mean levels established to protect the public welfare from any known or anticipated adverse effects, such as injury to agricultural crops and livestock, damage to or deterioration of property, annoyance and nuisance of persons, or hazards to air and ground transportation. (From MN Rule 7009.0010)