To characterize concentrations of atmospheric ammonia (NH3) at industrial parks in southern Taiwan, three representative industrial parks and two background locations were selected for this study. The sampling process for gaseous ammonia was performed in accordance with Taiwan EPA NIEA A426.71B. The results revealed that the mean NH3 levels ranged from 70.5 to 153.9 ppb (mean = 100.2 ppb) in Neipu Industrial Park. Both highest mean levels in Neipu Industrial Park during 12:00–13:00 in the daytime and during 20:00–21:00 at night were about 50–150 times greater than ambient background levels. For the whole day, the mean NH3 levels ranged from 43.0 to 114.6 ppb (mean = 72.8 ppb) in Pingtung Industrial Park. In Pingnan Industrial Park, the mean NH3 levels for the whole day ranged from 45.0 to 122.6 ppb (mean = 84.9 ppb). Moreover, the ratio values (Rs) were categorized according to the cover-range (from minimum ratios to maximum ratios) at different sampling periods and the minimum separated boundary lines. The results indicate that the characteristics of ratio values normalized by the background levels can be divided into three main categories in southern Taiwan: (1) R > 200; (2) R > 60; (3) R > 10. Our research data reveal obvious reasons for this clear distinction of ambient NH3 levels in southern Taiwan. Significantly, the results reveal that agricultural NH3 emissions influence local ambient concentrations of NH3.