Aerosols at Mt. Lemmon: Estimates of gas-to-particle conversion rate

As part of a research project to investigate sources, sinks and climate influence of aerosols we carried out measurements of the aerosol size (diameter), area and volume distributions from a summit location (2.8 km altitude) in the Catalina Mountains in southern Arizona. We find the air to be very clean with respect to aerosol concentration, in fact at certain times nearly as clean as the air at the Mauna Loa Observatory in the central Pacific Ocean. Chemical reactions involving aerosol surface, optical extinction and scattering are controlled by a sub micron and quite volatile (with respect to vapor pressure) `accumulation modeʹ. We present evidence suggesting that the gas-to-particle conversion rate in this mid-tropospheric locale is on the order of 10−19 g cm−3 s−1.