Chemical precursors of new particle formation in coastal New Zealand

Abstract. To reduce uncertainties in climate predictions, we need to better understand aerosol formation in different environments. An important part of this is studying which chemical species are responsible for particle formation. While many advances have been made in this field, measurements are lacking especially from marine environments. Here, we measured the chemical composition of ambient ions over 7 months at Baring Head station, located in coastal New Zealand. This adds to our previous work which reported the aerosol size distribution measurements and investigated new particle formation and environmental conditions favouring new particle formation at the station. By combining the information on ion chemical composition with our previous work, we were able to study the chemical precursors of new particle formation. Our results showed that while over land new particle formation is likely driven by sulfuric acid and organic species, in clean marine air iodine oxides and sulfur species are likely important drivers of particle formation processes. These data were also used to characterise the diurnal and seasonal cycles of most important ion groups and their geographical source regions. Sulfate ions displayed a clear daytime maximum where as iodine oxides had morning and evening maximums. Highly oxygenated organic molecules on the other hand, were most abundant during the night when the air was land-influenced. This data set is highly valuable and our results provide important information on the chemical species driving new particle formation at a remote Southern Hemisphere coastal site.