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14 Nitro-polycyclic aromatic hydrocarbons (NPAH) are ubiquitous in polluted air but little is 15 known about their abundance in background air. NPAHs were studied at one marine and one 16 continental background site i.e., a coastal site in the southern Aegean Sea (summer 2012) and 17 a site in the central Great Hungarian Plain (summer 2013), together with the parent 18 compounds, PAHs. A Lagrangian particle dispersion model was used to track air mass history. 19 Based on Lagrangian particle statistics, the urban influence on samples was quantified for the 20 first time as a fractional dose to which the collected volume of air had been exposed to. 21 At the remote marine site, the 3-4 ring NPAH (sum of 11 targeted species) concentration was 22 23.7 pg m -3 while the concentration of 4-ring PAHs (6 species) was 426 pg m -3 . 223 nitrofluoranthene (2NFLT) and 3-nitrophenanthrene were the most abundant NPAHs. Urban 24 fractional doses in the range <0.002–5.4% were calculated. At the continental site, the Σ11 325 4rNPAH and Σ6 4rPAH were 58 and 663 pg m -3 , respectively, with 9-nitroanthracene and 26 2NFLT being highest concentrated amongst the targeted NPAHs. The NPAH levels observed 27 in the marine background are the lowest ever reported and remarkably lower, by more than 28 one order of magnitude, than one decade before. Day-night variation of NPAHs at the 29 continental site reflected shorter lifetime during the day, possibly because of photolysis of 30 some NPAHs. The yields of formation of 2NFLT and 2-nitropyrene (2NPYR) in marine air 31 seem to be close to the yields for OH-initiated photochemistry observed in laboratory 32 experiments under high NOx conditions. Good agreement is found for prediction of NPAH 33 gas-particle partitioning using a multi-phase poly-parameter linear free energy relationship. 34 Sorption to soot is found less significant for gas-particle partitioning of NPAHs than for 35 PAHs. The NPAH levels determined in the southeastern outflow of Europe confirm 36 intercontinental transport potential. 37 38