Seasonal significance of new particle formation impacts on cloud condensation nuclei at a mountaintop location

Abstract. New particle formation (NPF) events are defined as a
sudden burst of aerosols followed by growth and can impact climate by
growing to larger sizes and under proper conditions, potentially forming
cloud condensation nuclei (CCN). Field measurements relating NPF and CCN are
crucial in expanding regional understanding of how aerosols impact
climate. To quantify the possible impact of NPF on CCN formation, it is
important to not only maintain consistency when classifying NPF events but
also consider the proper timeframe for particle growth to CCN-relevant
sizes. Here, we analyze 15 years of direct measurements of both aerosol size
distributions and CCN concentrations and combine them with novel methods to
quantify the impact of NPF on CCN formation at Storm Peak Laboratory (SPL),
a remote, mountaintop observatory in Colorado. Using the new automatic
method to classify NPF, we find that NPF occurs on 50 % of all days
considered in the study from 2006 to 2021, demonstrating consistency with
previous work at SPL. NPF significantly enhances CCN during the winter by a
factor of 1.36 and during the spring by a factor of 1.54, which, when combined with
previous work at SPL, suggests the enhancement of CCN by NPF occurs on a
regional scale. We confirm that events with persistent growth are common in
the spring and winter, while burst events are more common in the summer and
fall. A visual validation of the automatic method was performed in the
study. For the first time, results clearly demonstrate the significant
impact of NPF on CCN in montane North American regions and the potential for
widespread impact of NPF on CCN.
