Persistent daily new particle formation at a mountain-top location

Frequent new particle formation (NPF) has been observed regularly at Storm Peak Laboratory, a high elevation mountain-top observatory in Colorado. These events occurred during 52% of the 474 measurement days from 2001 to 2009, consistently during the mid-afternoon throughout the spring, summer and winter months. Average growth rates, condensation sinks, and formation rates are presented. The strongest correlation factor with NPF is ultraviolet radiation. The events are not related to increased ozone concentration or pre-existing aerosol surface area, implying that nucleation can occur anywhere in the free troposphere.