Semi-volatile secondary organic aerosol in urban atmospheres: meeting a measurement challenge

Abstract Ammonium nitrate and semi-volatile organic compounds are significant components of fine particles in urban atmospheres. These components, however, are not properly determined with current US EPA accepted methods such as the PM 2.5 FRM or other single filter samplers due to significant losses of semi-volatile material (SVM) from particles collected on the filter during sampling. Continuous PM 2.5 mass measurements are attempted using methods such as the RP The majority of semi-volatile fine particulate organic material is secondary organic aerosol. • This semi-volatile organic aerosol is not retained on the heated filter of a regular TEOM monitor and hence is not measured by this sampling technique. In addition, secondary ammonium nitrate is also lost. • Much of the semi-volatile organic aerosol is also lost during sampling from single filter samplers such as the PM 2.5 FRM sampler. • The amount of semi-volatile organic aerosol lost from single filter samplers can vary from less than 1 3 that lost from heated TEOM filters during cold winter conditions to essentially all during warm summer conditions. • Semi-volatile organic aerosol can only be reliably collected using an appropriate denuder sampler. • Either a PM 2.5 FRM sampler or the IMPROVE sampler can be easily modified to a denuder sampler with filters which can be analyzed for semi-volatile OC, nonvolatile OC and EC using existing OC/EC analytical techniques. The research upon which these statements are based is summarized in this document.