The influence of modification by pre- and post-treatment of active carbons with ammonia on adsorption abilities from liquid and gas phases has been tested. Carbon materials with different surface chemistry were obtained by chemical activation of Polish brown and subbituminous coal. The products were microporous active carbon samples of well developed surface area (S_BET from 1579 to 2,922 m²/g), containing from 0.3 to 7.4 wt% of nitrogen. The results obtained in our study have, moreover, proven that a suitable choice of the modification procedure for coals can produce activated carbons with high capacity of iodine adsorption (to 2,100 mg/g) and high nitrogen dioxide adsorption ability, reaching to 55.1 mg NO₂/g.