Peroxyacetyl nitrate and peroxypropionyl nitrate during SCOS 97-NARSTO

Area of Science:

• Atmospheric Chemistry
• Air Quality Research
• Environmental Science

Background:

• Peroxyacyl nitrates (PANs) are significant in urban air quality and tropospheric chemistry.
• They are recognized as mutagens, phytotoxins, and potential indicators of fuel composition changes.
• Understanding PAN and PPN concentrations is crucial for assessing air pollution dynamics.

Purpose of the Study:

• To measure ambient concentrations of PAN and PPN in Southern California during summer 1997.
• To compare these concentrations with historical data and assess the impact of reformulated gasoline.
• To analyze diurnal variations and the role of thermal decomposition in PAN levels.

Main Methods:

• Ambient air sampling for PAN and PPN at Azusa and Simi Valley, Southern California.
• Continuous monitoring from June to October 1997.
• Analysis of concentration ratios, diurnal patterns, and thermal decomposition effects.

Main Results:

• Highest concentrations observed were 4.8 ppb for PAN and 0.72 ppb for PPN in Azusa.
• Ambient PAN and PPN levels in 1997 were lower than in 1990, 1991, and 1993.
• PPN/PAN ratios remained consistent, similar to pre-reformulated gasoline levels.
• PAN thermal decomposition significantly contributed to observed PAN levels, especially at higher temperatures.

Conclusions:

• Summer 1997 PAN and PPN levels in Southern California were lower than in previous years.
• The PPN/PAN ratio remained stable, suggesting limited impact from California Phase 2 reformulated gasoline on this metric.
• Thermal decomposition plays a substantial role in daytime PAN concentrations, particularly under warm conditions.