NIST currently supports AIGER members by maintaining reasonable inventories of required gas SRMs that consist of dilute mixtures of key pollutants such as carbon dioxide, carbon monoxide, hydrocarbons, and nitric oxide. Newer vehicles produce lower levels of these pollutants because their engines employ fuel injection with air-to-fuel ratios optimized by an on-board computer and emissions reduced by efficient catalytic converters. During testing the tailpipe exhaust levels are diluted with clean air and collected using constant volume sampling bags or new mini-diluter technology. AIGER stakeholders have identified the need for gas standards with significantly lower concentrations of carbon monoxide, carbon dioxide, hydrocarbons, and nitric oxide.
NIST has responded to AIGER needs by developing four new SRMs with significantly lower concentrations of carbon dioxide, nitric oxide, and propane. They are:
SRM 2737 (500.0 ± 7.5) nmol/mol nitric oxide in nitrogen
SRM 2738 (1000 ± 15) nmol/mol nitric oxide in nitrogen
SRM 2765 (100.0 ± 0.6) nmol/mol propane in air
SRM 2617 (500.0 ± 1.0) µmol/mol carbon dioxide in nitrogen
Nitric oxide and propane are precursors to smog formation. The new SRMs allow lower levels of these precursors to be monitored. It is estimated that when the regulations are fully implemented in 2010, smog-forming emissions in the Los Angeles area will be reduced by 57 tons per day. SRM 2617 is a high-accuracy carbon dioxide standard that will be used to measure fuel economy.
Research to minimize cylinder wall off-gassing of NO over time will be studied.