Variation in characteristics of air concentrations of NH3, NO2 and O3 induced by applications of urea in soils of plastic greenhouses in suburban China

Few studies have been carried out so far for measuring concentrations of NH3, NO2 and O3 in plastic greenhouses. In this study, NH3, NO2 and O3 concentrations were measured with passive sampler technology in a plastic greenhouse located in the Changsha suburb in southern China over a one and a half month period (November 30, 2008 to January 11, 2009). Soil in the greenhouse was subjected to four treatment (T) types (no N fertilizer T1, common urea T2, coated urea T3 and common urea with nitrification inhibitor dicyandiamide (DCD) T4. The average concentrations (μg/m3) of NH3, NO2 and O3 in descending order was: T4 (31.66) > T2 (25.93) > T3 (23.52) > T1 (7.96), T2 (10.99) > T3 (8.16) > T4 (7.48) > T1 (5.20), T2 (75.05) > T3 (64.20) > T4 (63.85) > T1 (49.02), respectively. This implied that photochemical reactions took place and that harmful gases accumulated after application of N fertilizer in the plastic greenhouse. DCD inhibited the conversion of ammonium to nitrate, increased NH3 volatilization and decreased NO2 level. The coated urea decreased the emissions of NH3 and increased nitrogen use efficiency. We found significant positive correlations (p < 0.01) between temperature and both NH3 and NO2 levels. Correlations between soil pH and both NH3 and NO2 concentrations were also significant (p < 0.01). The O3 average concentration from March 31, 2009 to April 10, 2009 in the higher latitude of the Yinchuan suburb in northern China was two times greater than that in the Changsha suburb in southern China. The O3 daily concentrations in the Yinchuan suburb exceeded 160 μg/m3 (i.e., China's Grade I standard), and the maximal value 214.83 μg/m3 exceeded 200 μg/m3 (i.e., China's Grade III standard).