Environmental toxicity of the major acidic pollutants in the flue gas mixtures has long been well known. This study addresses of using Synechococcus sp. and Chlorella sp. as effective biomaterials in their tolerance to SO2 and NO2 and improving their growth and survival by addition of triacontanol (TRIA) and sodium bicarbonate (NaHCO3) to the culture medium. The cultures were exposed to SO2 or NO2 for 10', 15', and 20' periods at the 10th day of incubation. Optimum pH was found as 7.5 for Synechococcus sp. and 8.5 for Chlorella sp. at 10' exposure to SO2 or NO2 gas. Toleration of both microalgal cultures towards NO2 was better than SO2. Chlorella sp. had much more tolerance to acidic pollutants than Synechococcus sp. Chlorophyll a concentration of Synechococcus sp. was 0.142 mu g/mL at 15' exposure to SO2, 0.130 mu g/mL at 20' exposure to SO2, 0.296 mu g/mL at 15' exposure to NO2, and 0.142 mu g/mL at 20' exposure to NO2. Chlorophyll (a + b) concentration of Chlorella sp. was 0.667 mu g/mL at 15' exposure to SO2, 0.493 mu g/mL at 20' exposure to SO2, 0.800 mu g/mL at 15' exposure to NO2, and 0.510 mu g/mL at 20' exposure to NO2. This study highlights the potential of using Synechococcus sp. and Chlorella sp. in tolerance to NO2 and SO2 from flue gas mixtures at least. (C) 2012 Elsevier Ltd. All rights reserved.