Aerosol optical depth over Lauder, New Zealand

Aerosol optical depths (AOD) measured over Lauder in Central Otago, New Zealand in 1996–1997, and continuously since 1999, are amongst the lowest observed worldwide. The Lauder measurements show a seasonal cycle in AOD with a winter minimum and summer local maximum, and there is a springtime peak that is probably due to biomass burning. The wavelength dependence of AOD suggests a relatively stable size distribution but smaller average particle size in spring. Lack of correlation with surface humidity below 90% RH, in both AOD and wavelength dependence, may constrain the likely composition of the aerosol. There was a downward but insignificant trend in mean AOD over the measurement period.