<p><strong>Abstract.</strong> Nitro-monoaromatic hydrocarbons (NMAHs), such as nitrocatechols, nitrophenols and nitrosalicylic acids, are important constituents of atmospheric particulate matter (PM) water soluble organic carbon (WSOC) and humic-like substances (HULIS). Nitrated and oxygenated derivatives of polycyclic aromatic hydrocarbons (NPAHs, OPAHs) are toxic and ubiquitous in the ambient air; due to their light absorption properties, together with NMAHs they are part of aerosol brown

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... on (BrC). We investigated the winter concentrations of these substance classes in size-resolved particulate matter (PM) from two urban sites in central and southern Europe, i.e. Mainz (MZ), Germany and Thessaloniki (TK), Greece. ∑₁₁NMAH concentrations in PM₁₀ and total PM were 0.51&amp;ndash;8.38 and 12.1&amp;ndash;72.1&amp;thinsp;ng&amp;thinsp;m^&amp;minus;3 at MZ and TK site, respectively, whereas ∑₈OPAHs were 47&amp;ndash;1636 and 858&amp;ndash;4306&amp;thinsp;pg&amp;thinsp;m^&amp;minus;3, and ∑₁₇NPAHs were ≤&amp;thinsp;90 and 76&amp;ndash;578&amp;thinsp;pg&amp;thinsp;m^&amp;minus;3, respectively. NMAHs and the water-soluble OPAHs contributed 0.4 and 1.8&amp;thinsp;%, and 0.0001 and 0.0002&amp;thinsp;% to the HULIS mass, at MZ and TK, respectively. The mass size distributions of the individual substances generally peaked in the smallest or second smallest size fraction i.e., <&amp;thinsp;0.49&amp;thinsp;µm or 0.49&amp;ndash;0.95&amp;thinsp;µm. The mass median diameter (MMD) of NMAHs was 0.10&amp;thinsp;µm and 0.27&amp;thinsp;µm at MZ and TK, respectively, while the MMDs of NPAHs and OPAHs were both 0.06&amp;thinsp;µm at MZ, and 0.12 and 0.10&amp;thinsp;µm at TK. Correlation analysis between NMAHs, NPAHs and OPAHs from one side and WSOC, HULIS, nitrate, sulphate and potassium cation (K⁺) from another, suggested that the fresh biomass burning emissions dominated at the TK site, while aged air masses (influenced by biomass and fossil fuel burning) were predominant at the MZ site.</p>