Atmospheric Observations of Aerosol Sizes, Sulfuric Acid and Ammonia Measured in Kent, Ohio

Atmospheric particles affect atmospheric composition, cloud formation, global radiation budget, and human health. Nucleation is a gas-to-particle conversion process in which new particles form directly from gas phase species and is a key process that controls particle number concentrations. The most common feature of the new particle formation events is a substantial increase of number concentrations of nucleation mode particles reaching up to 105-106 cm-3 in the condensable vapor-laden air. There are several nucleation mechanisms for tropopsheric aerosol formation, but it is unclear which nucleation process dominates. In particular, observations and modeling studies show that ammonia can be important for atmospheric nucleation in the boundary layer, but simultaneous measurements of aerosol sizes and precursors including sulfuric acid and ammonia are critically lacking. In order to overcome these shortcomings, we conduct atmospheric observations of new particle formation in Kent, OH. We have measured aerosol sizes and concentrations for particles in the size range from 3-102 nm semi- continuously from December 2005 and for particles from 3-1000 nm continuously from September 2007 in Kent State campus, Kent, OH (with an inlet placed at ~11.5 m above ground level). We also simultaneously measure sulfuric acid and ammonia, two most important inorganic aerosol precursors, with two chemical ionization mass spectrometers (CIMS) from August 2008. Kent, located in Northeastern Ohio, is relatively rural itself, but is also surrounded by several urban cities within 40 miles. Because of the combination of its relatively rural environment (hence low surface areas of aerosol particles), active vegetation (organic and NH3 emissions), and possible transport of aerosol precursors from the surrounding urban and industrialized areas, Kent is a unique location to make new particle formation studies. So far, most of new particle formation observations made typically in US were at relatively polluted areas (e.g., Atlanta, Pittsburgh, and Detroit). We will present our ground-based, long-term measurements of aerosol sizes and concentrations and discuss how aerosol precursors (H2SO4 and NH3), RH, temperature and photochemistry affect new particle formation in this rather rural Midwestern town, by comparing with previous new particle formation observations made in other sites (e.g., EPA supersites in relatively polluted atmosphere and in Finland boreal forest).