Atmospheric fine particle mass mostly originates from emissions from motor vehicles, wildfires and other combustion processes. When emissions are exposed to oxidants and sunlight, they evolve chemically and physically to generate secondary particulate matter. Dr. Allen L. Robinson, Head of the Department of Mechanical Engineering at Carnegie Mellon University, shared results from their investigations of atmospheric evolution of emissions at the SOCAAR Seminar on February 1, 2017.

Dr. Robinson spoke about the investigation of gasoline vehicles to characterize secondary organic aerosol formation and primary emissions. 84 vehicles ranging from the 1980s to 2014 were tested. Due to more stringent regulations, newer vehicles showed decreasing secondary organic aerosol production. Improvements in engine control and catalytical converter technology are the main reason for the dramatic reduction in emissions. But the secondary organic aerosol reduction observed was less than expected as new regulations were adopted.

In fact, although vehicles are getting a lot cleaner, lots of secondary organic aerosol production from light duty gasoline vehicles exhaust were still observed. Dr. Robinson believe that the chemistry of the atmosphere, shifting from a low to high NOx regime is a factor. He believes that further investigations are needed to understand how NOx influence secondary organic aerosol formation, and the implications of the findings on human exposure, climate and design of regulations to control pollutant emissions.