AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Characterizing the Influence of Transport Variability on Aerosol Concentrations at Mauna Loa Observatory
LAUREN POTTER, Sonia Kreidenweis, Molly Morman, Barry Huebert, Steven Howell, John Zhuang, Colorado State University
Abstract Number: 550 Working Group: Remote and Regional Atmospheric Aerosols
Abstract Located in the remote Pacific Ocean at an elevation of nearly 4 kilometers above sea level, Mauna Loa Observatory (MLO) is an ideal and unique measurement site for ground-based, free tropospheric observations. This study makes use of a unique, 20-year data set of aerosol ionic composition, obtained by the University of Hawaii at Manoa. Collections of daily filter samples were made during nighttime downslope (free-tropospheric) transport conditions, from 1989 to 2009, and were analyzed for the following species: HNO3(g), and aerosol-phase concentrations of NO$_3$^-, SO$_4$^(2-), MSA, Cl$^-, Oxalate, Na$^+, NH$_4$^+, K$^+, Mg$^(2+), and Ca$^(2+). Understanding the factors involved in seasonal and interannual variations in aerosol speciation and concentrations at this site are complicated by the relatively short lifetimes of aerosols, compared with many greenhouse gases that have also been sampled over long time periods at MLO. Our study applies a combination of back trajectories and climate indices to interpret the relative roles of large-scale transport variability and variability in aerosol primary and secondary emissions, on the overall observed aerosol variability.
We find that aerosol concentrations at MLO were highly influenced by variations in transport efficiency in this portion of the central Pacific, which is highly dependent on synoptic variations due to the El-Niño Southern Oscillation. The degree of Asian continental influence at MLO during late winter/early spring was shown to be strongly related to such circulation characteristics, similar to observations for greenhouse gases. We further find a trend in springtime sulfate aerosol concentrations at MLO of 6%/year over the time period studied, significant at the 95% confidence level. This trend reflects, at least in part, estimated increasing trends in Asian anthropogenic emissions over the same time period, that are superimposed on the variability in transport efficiency.