Lignin pyrolysis products that generated by biomass burning can conduce to the formation of secondary organic aerosols (SOA), especially in municipal environments. 3-Methylcatechol (3-MC) and 4-Methylcatechol (4-MC) were selected as a representative congener of lignin pyrolysis product to investigate its fate both in the atmosphere and in aqueous particles. This work aims to summarize the reaction rules of this kind of compound, evaluate the contribution of such previously unconsidered reactions to the SOA formation from methylcatechols, and to provide a solution for the optimization of the water environment of such pollutants. We performed quantum chemical calculations for the O-3-intiated further reactions of the Criegee intermediates (generated during the primary reaction) with NO (only in the gas phase), H2O and O-2. Using kinetic simulation, the calculated total rate constant (at 298 K and 1 atm) of O-3-initiated reactions of 3-MC and 4-MC are 7.89 x 10(-17) and 1.11 x 10(-17)cm(3) molecule(-1) s(-1). For the lignin pyrolysis products in this work and our previous studies, atmospheric lifetime comparison shows that the reactivity of these compounds takes the order 3-methylcatechol > 4-methylcatechol > catechol > methoxybenzene, which is consistent with experimental results. The ecotoxicity assessment shows majority of the toxic intermediates and intermediate products are converted into harmless compounds after ozone addition reactions.