he instrument indicated a CO2 con- centration that was always higher (ranging from 0.33 to 3.33%) in comparison to nearby atmospheric levels the trails, a high rate of NOx at the beginning of each trial (4.4, 5.9 and 3.9 mg Nm3 in the first, second and third year, respectively) and limited emissions of aldehydes, ammonia, aliphatic amine and VOCs from the composting piles.