[Effects of the Crop Rotation on Greenhouse Gases from Flooded Paddy Fields].

A field experiment was conducted at the Key Field Station for Monitoring Eco-environment of Purple Soil of the Ministry of Agriculture of China in the farm of Southwest University, Chongqing. The static chamber and gas chromatography method was used to study the effect of the cropping systems on greenhouse gases from rice-fallow (RF), rice-rapeseed rotation (RR), and rice-brussel mustard rotation (RV) cropland in situ for a year. An opaque chamber was used for CH4 and N2O observations and a transparent chamber was utilized for CO2 observations. The results show that the annual cumulative CH4 emissions from different crop rotations were (CH4, kg·hm-2) RF (422.87±27.1) > RR (132.05±23.11) > RV (50.91±3.83). The RV and RR were significantly lower than RF (P<0.05). The annual cumulative emissions of N2O[N2O, kg·hm-2] were RV (21.38±6.51) > RR (20.02±5.23) > RF (0.48±0.02). The RV and RR were significantly higher than RF (P<0.05). The annual net cumulative emissions of CO2 were (CO2, t·hm-2) RR (-55.43±5.04) > RV (-29.1±3.00) > RF (-14.08±1.81). The RV and RR were significantly higher than RF (P<0.05). At the time scale of 100 a, the integrated global warming potentials (GWP) of CH4, N2O, and CO2 were (CO2, t·hm-2)RR(-46.43) > RV(-22.01) > RF(-2.11), indicating that converting flooded paddy fields to paddy-upland crop rotation systems notably increases the potential increment of carbon sinks. Compared with RV, RR has a better effect, which suggests that rice-rapeseed rotation is the most effective measure for the escalation of carbon sinks of ecosystems in the southwestern area.

[Pollution Characteristics of Organic Carbon and Elemental Carbon in Atmospheric Aerosols in Beibei District, Chongqing].

To study the pollution characteristics of atmospheric carbon aerosols, aerosol samples were collected via a cascade impactor (Andersen) from March 2014 to February 2015 in Beibei District, Chongqing. Organic carbon (OC) and element carbon (EC) were detected using a DRI 2001A carbon analyzer. The results showed that the annual average concentrations of OC and EC in PM2.1 were (16.3±7.6) and (1.8±0.7), respectively, and (25.0±9.6), and (3.2±1.3) µg·m-3, respectively, in PM9.0. The concentrations of both OC and EC were higher in winter and spring than in summer and autumn for PM2.1, whereas, for PM9.0, the concentration of OC was higher in summer and spring than in winter and autumn and that of EC was higher in winter and spring than in summer and autumn. The particle size distributions of OC and EC for the study year were analyzed, and it was found that those of OC were bimodal, with peaks in the size ranges of 0.43-0.65 µm for fine particles and 4.7-5.8 µm for coarse particles, and those of EC were trimodal, with peaks in the size ranges of 0.43-0.65 µm for fine particles and 4.7-5.8 µm for coarse particles and a concurrent significant peak in the particle size range of 2.1-3.3 µm. In addition, the correlations between OC and EC were analyzed and the SOC in PM2.1 was estimated. It was found that the average concentration of SOC was (6.3±5.9) µg·m-3, which accounted for 33.5%±22.6% of the OC concentration in Beibei District. Furthermore, OC and EC were significantly correlated. Finally, the pollution sources of atmospheric aerosols in Beibei were analyzed, and it was found that the pollution in Beibei mainly came from the exhaust gas of gasoline vehicles, biomass combustion, and coal combustion.