Technical note: A 23-year record of twice-weekly aerosol composition measurements at Mauna Loa Observatory

This paper introduces a newly compiled data set of atmospheric particulate matter (PM) measurements from 1988 through 2010 at Mauna Loa Observatory (MLO), Hawaii, USA. The data are from two samplers: one running only during nighttime hours over multiple days and another running continuously over the same days. The objective of the night-only schedule is to capture samples from Pacific background air masses transported in the free troposphere with minimal contamination from local and marine emissions. Elements characteristic of soils generally exhibit similar concentrations between the continuous and night-only samples, which suggests Pacific background air masses are responsible for the majority of the fine soil aerosol observed at MLO. Sulfur concentrations in the continuous samples often substantially exceed those in night-only samples, suggesting that local sources contribute to the daytime S concentrations at MLO. Trends estimated from Thiel-Sen regression for all 23 years are 1.3% and −1.7% per year for S and Fe (significant at p = 0.05) in the night-only samples; S and Fe trends in the last 10 years are in the same directions and stronger (4.2% and −4.4% per year).