Fig. 1. Ammonia concentration gradients with height during winter and summer and over lagoons of different ammonium concentrations: (a) North Carolina farrow-to-finish farm number 10 at 0800 h on 22 Jan. 1998, (b) North Carolina farrow-to-finish farm number 20 at 0800 h on 2 Feb. 1998, (c) North Carolina farrow-to-finish farm number 10 at 0800 on 5 Aug. 1997, and (d) North Carolina farrow-to-finish farm number 20 at 0800 on 7 Aug. 1997.