The effectiveness of algae to treat NO2and NO in simulated flue gas was tested using Chlorella vulgaris in photobioreactors (PBRs) using NOxconcentrations between 30 ppm to 780 ppm. NOxdissolved and reacted in water to form NO3-and NO2-in the PBR growth medium, providing a nitrogen source that the algae readily assimilated for cell synthesis. Three 20-L photobioreactors were inoculated with a pure culture of C. vulgaris prepared in Bristol growth medium and algae were grown in the PBRs at 25°C and pH of 7.0 in a modified Bristol medium that did not contain nitrogen compounds. The C. vulgaris grew substantially using NO3-/NO2-as its nitrogen source for cell synthesis. The NO3-and NO2-were formed through the dissolution and oxidation/reduction of NOxfrom the simulated flue gas. Algal growth by assimilation of NO3-and/or NO2-allowed for continual dissolution of NOx, resulting in NOxremoval rates from the gas phase of up to 97%, with residual nitrogen of up to 7 mg-N/L in solution. Algae grew from an initial cell density of 3.1 x 105cells/L to cell densities of up to 1.85 x 107cells/mL and dry weights of up to 243 mg/L. Cell nitrogen content varied from 4-8%. PBR to treatment of gaseous NOxwas analyzed in terms of mass transfer rates, chemical kinetics, and biological growth.