The oxidation of biogenic and anthropogenic compounds leads to the formation of secondary organic aerosol mass (SOA). The present study aims to investigate Î±-pinene, limonene, and m-cresol with regards to their SOA formation potential dependent on relative humidity (RH) under night- (NO.sub.3 radicals) and daytime conditions (OH radicals) and the resulting chemical composition. It was found that SOA formation potential of limonene with NO.sub.3 under dry conditions significantly exceeds that of the OH-radical reaction, with SOA yields of 15-30 % and 10-21 %, respectively. Additionally, the nocturnal SOA yield was found to be very sensitive towards RH, yielding more SOA under dry conditions. In contrast, the SOA formation potential of Î±-pinene with NO.sub.3 slightly exceeds that of the OH-radical reaction, independent from RH. On average, Î±-pinene yielded SOA with about 6-7 % from NO.sub.3 radicals and 3-4 % from OH-radical reaction. Surprisingly, unexpectedly high SOA yields were found for m-cresol oxidation with OH radicals (3-9 %), with the highest yield under elevated RH (9 %), which is most likely attributable to a higher fraction of 3-methyl-6-nitro-catechol (MNC). While Î±-pinene and m-cresol SOA was found to be mainly composed of water-soluble compounds, 50-68 % of nocturnal SOA and 22-39 % of daytime limonene SOA are water-insoluble. The fraction of SOA-bound peroxides which originated from Î±-pinene varied between 2 and 80 % as a function of RH. Furthermore, SOA from Î±-pinene revealed pinonic acid as the most important particle-phase constituent under day- and nighttime conditions with a fraction of 1-4 %. Other compounds detected are norpinonic acid (0.05-1.1 % mass fraction), terpenylic acid (0.1-1.1 % mass fraction), pinic acid (0.1-1.8 % mass fraction), and 3-methyl-1,2,3-tricarboxylic acid (0.05-0.5 % mass fraction). All marker compounds showed higher fractions under dry conditions when formed during daytime and showed almost no RH effect when formed during night.