Increase in secondary organic aerosol in an urban environment

Abstract. The evolution of fine aerosol (PM1) species as well the contribution potential sources to total organic (OA) at an urban background site in Barcelona, western Mediterranean basin (WMB) was investigated. For this purpose, a quadrupole chemical speciation monitor (Q-ACSM) deployed acquire real-time measurements for two 1-year periods: May 2014–May 2015 (period A) and September 2017–October 2018 B). Total PM1 concentrations showed slight decrease (from 10.1 9.6 µg m−3 from A B), although relative inorganic compounds varied significantly. Regarding compounds, SO42-, black carbon (BC) NH4+ significant period B (−21 %, −18 % −9 respectively), whilst NO3- were higher (+8 %). Source apportionment revealed OA contained 46 70 secondary (SOA) periods B, respectively. Two oxygenated (OOA) differentiated by their oxidation status (i.e. ageing): less oxidized (LO-OOA) more (MO-OOA). Disregarding winter periods, when LO-OOA production not favoured, transformation into MO-OOA found be effective B. lowest LO-OOA-to-MO-OOA ratio, excluding winter, September–October (0.65), implying accumulation aged after high temperature solar radiation conditions summer season. In addition temperature, SOA (sum OOA factors) enhanced exposure NOx-polluted ambient other pollutants, especially O3 during afternoon hours. anthropogenic primary identified, cooking-related (COA), hydrocarbon-like (HOA), biomass burning (BBOA), decreased both absolute (as whole, 44 30 respectively). However, proportion grew rapidly highly polluted episodes. influence certain atmospheric episodes on also assessed. Both factors boosted with long- medium-range circulations, those coming inland Europe (triggering mainly MO-OOA) breeze-driven regional circulation (mainly LO-OOA). contrast, POA either air-renewal or stagnation anticyclonic events.