Arctic spring and summertime aerosol optical depth baseline from long-term observations and model reanalyses – Part 2: Statistics of extreme AOD events, and implications for the impact of regional biomass burning processes

Abstract. In a companion paper (Xian et al., 2022, part 1 of the study), we present an Arctic aerosol optical depth (AOD) climatology and trend analysis for 2003–2019 spring summertime periods derived from combination reanalyses, remote-sensing retrievals, ground observations. Continued previous discussion as second study, report statistics trends AOD extreme events using U.S. Navy Aerosol Analysis Prediction System ReAnalysis version (NAAPS-RA v1), sun photometer data AErosol RObotic NETwork (AERONET) sites, oceanic Maritime Network (MAN) measurements. Here, are defined with exceeding 95th percentile (denoted “AOD95”) distributions given locations 6-hourly or daily data. While AERONET MAN estimate median 550 nm value to be 0.07, is 0.24. Such dominated by fine-mode particles, largely attributable biomass burning (BB) smoke North American Arctic, Asian most areas Ocean. However, lower European more anthropogenic biogenic fine particles. The extreme-event occurrence dominance sea salt limited Atlantic Norwegian Sea. amplitudes are, however, significantly than those regions where dominant. Even sites distant BB source regions, principal driver variation above AOD95 threshold. Maximum values in high 2010–2019 have increased compared 2003–2009, indicating stronger influence recent years. tended equally distributed over all months (April–August) during 2003–2009 period while being concentrated late season (July–August) period. temporal shift likely due improved control early-season agriculture burning, climate-change-related increases lightning frequencies, reduction pollution