Implications of Organic Mass to Carbon Ratios Increasing Over Time in the Rural United States Journal of Geophysical Research: Atmospheres

The thermal evolution procedure used by most monitoring programs in the United States to determine carbonaceous aerosol concentrations is referred to as the thermal ‐optical re flectance method, where an aerosol sample that has been collected on a quartz filter is heated and evolved carbon is characterized as either organic (OC) or light absorbing carbon (LAC). Evolved carbon assigned to OC is multiplied by a factor, Roc, to achieve an estimate of organic mass. Over the last 10 –15 years, Roc, estimated through multiple linear regression analysis of data collected in the Interagency Monitoring of ProtectedVisual Environments (IMPROVE) program, has increased at about a rate of about 0.02 per year, reaching values above 2.0 in many regions of the United States. Analysis of evolved carbon concentration temporal