The main objective of the present study is the assessment of the non-radiative impact on the lower troposphere air quality of the intense biomass burning events that took place in the Eastern Mediterranean, when wild forest fires were burning in Peloponnesus (Greece) at the end of August 2007. The MM5-CAMx modeling system was applied in the Eastern Mediterranean in high spatial and temporal resolution for the period 23 to 31 August 2007, forced by biomass burning emission fluxes from the Global Fire Emissions Database (version 3.0), in day-to-day temporal and 0.1° spatial variability from the Global Fire Assimilation System. Enhancements of the CO and NOx concentrations over almost the entire modeling domain were estimated due to the biomass burning, which were more pronounced over the burnt areas and maximum over the Peloponnesus forest fires. The domain-wide near surface mean concentration was higher by +6% for CO and +11% for NOx because of the biomass burning. The near surface O3 values were reduced over the fire hot spots but increased over the greater part of the modeling domain. On the 26th August 2007, the maximum O3 concentrations reduction of about 12ppb (i.e. -34%) was calculated over the Peloponnesus fires while the highest O3 increase of about 27ppb (i.e. +52%) was estimated over the sea at 500km downwind the Peloponnesus large forest fires. The process analysis revealed that on that day, the inclusion of the biomass burning emissions resulted in an enhancement of the daytime gas phase O3 production in the boundary layer in the Eastern Mediterranean and during some daytime hours in a change of the chemical regime from O3 destruction to O3 production. From 6 to 16 UTC, the O3 photochemistry in the boundary layer was VOC-sensitive close to the Peloponnesus fires, gradually changing to NOx-sensitive in the downwind fire plume. In the same period, the maximum impact on the oxidizing capacity of the boundary layer was an increase by 0.25ppt for OH and a reduction by 13ppt for HO2 mean concentrations over the Peloponnesus forest fires and an increase by 12ppt for HO2 in the downwind plume.