Measurements of new particle formation and ultrafine particle growth rates at a clean continental site

TLDR

The study builds on aerosol measurement techniques previously used at the Mauna Loa Observatory, applying them to the remote continental site of Idaho Hill, Colorado. Researchers conducted simultaneous measurements of aerosol particles and their expected gas‑phase precursors at Idaho Hill, Colorado. New particle formation at Idaho Hill was strongly linked to high sulfuric acid concentrations, with growth rates 5–10 times higher than predicted by sulfuric acid alone, indicating additional nucleation and growth species beyond H₂SO₄. Citation: Weber et al., 1995.

Abstract

Simultaneous measurements of aerosol particles and their expected gas phase precursors were made at Idaho Hill, Colorado, a remote continental site. This study used apparatus and techniques similar to those employed in an earlier study at the Mauna Loa Observatory, Hawaii [ Weber et al. , 1995]. New particle formation, identified by the presence of ultrafine particles (nominally 3 to 4 nm diameter), was commonly observed in downslope (westerly) air and was correlated with high sulfuric acid (H 2 SO 4 ) concentrations, low relative humidity and low particle surface area concentrations. The data point to H 2 SO 4 as a principle nucleation precursor species with typical daytime concentrations between 10 6 and 10 7 molecules cm −3 . Particle production was observed at H 2 SO 4 concentrations that are well below predicted values for binary nucleation of H 2 O and H 2 SO 4 , suggesting that another species participated. Particle growth rates were estimated from the data with two independent approaches and in both cases were ∼5 to 10 times higher than can be explained by condensation of H 2 SO 4 and its associated water. This suggests that species in addition to H 2 S0 4 were also making large contributions to ultrafine particle growth. Finally, calculated steady‐state H 2 SO 4 concentrations were found to be in good agreement with measured values if the mass accommodation coefficient for H 2 SO 4 on aerosol surfaces was assumed equal to ∼1.