Characteristics of NO Emission from Typical Saline Soil of Southern Shanxi Cotton Land

NO is a primary air pollutant and fertilized farmland is globally the second largest source of atmospheric NO. Development of mitigation strategies to relieve air pollution requires understanding the characteristics and quantifying the amounts of NO emissions from cultivated saline soils. The authors carried out yearround continuous measurements of NO fluxes from the typical saline soil cultivated with cotton in southern Shanxi and applied with a pure nitrogen fertilizer at 663 kg·hm-2·a-1. An automated system based on static chamber technique and online chemiluminescent analysis was employed for the measurements. The results showed that increasing measurement intervals to better capture diurnal variability was more essential than increasing spatial replicates of observations, in terms of annual emission quantification. The NO emission showed an obvious pattern of seasonal variation, with intensive fluxes appearing in spring and early summer, especially after nitrogen fertilization, and marginal emissions occurring in the remaining period of the year. The diurnal variation pattern with singlepeak commonly appeared under clear weathers. The maximum diurnal fluxes of the daypeak pattern mostly appeared about 3 h earlier than that of soil (5 cm) temperature. The background NON emission was estimated at about 0.64 kg·hm-2·a-1. Meanwhile, the annual direct NO emission factor of applied nitrogen fertilizers was quantified as 0.32%±0.09%. While this study revealed some important characteristics of NO emission from saline soils cultivated with cotton, it also provided emission factors for compiling inventories of NO emissions from croplands.