Simulating Dry Deposition Fluxes of PM_(10) and Particulate Inorganic Nitrogen over the Eastern China Seas During a Severe Asian Dust Event Using WRF-Chem Model

A WRF-Chem model including a comprehensive gas-phase nitrogen chemistry module was used to simulate a severe dust event appearing in the eastern China on 19-25 March, 2002. The modeling result well reproduced PM10 concentrations in various distances from the dust sources and the transport pathway of the dust strom. The results showed that both the concentrations and the dry deposition fluxes of PM10 increased over the China seas during the dust event following the passage of a cold front system. The maximum fluxes of PM10 in the Yellow Sea and the East China Sea during the dust event were 5.5 and 8.4 times of those before the event, respectively. However, the temporal variations of the dry deposition fluxes of particulate inorganic nitrogen differed over the Yellow Sea from those over the East China Sea. Nitrate and ammonium in the whole northern China rapidly decreased because of the intrusion of dust-loaded air on 19 March. The dust plume arrived in the Yellow Sea on 20 March, decreasing the particulate inorganic nitrogen in mass concentration accordingly. The minimum dry deposition fluxes of nitrate and ammonium in the Yellow Sea were about 3/5 and 1/6 of those before the dust arrival, respectively. In contrast, when the dust plume crossed over the Yangtze Delta area, it became abundant in nitrate and ammonium and increased the concentrations and dry deposition fluxes of particulate inorganic nitrogen over the East China Sea, where the maximum dry deposition fluxes of nitrate and ammonium increased approximately by 4.1 and 2.6 times of those prior to the dust arrival.

Reducing nitrogen runoff from paddy fields with arbuscular mycorrhizal fungi under different fertilizer regimes

Nitrogen（N） runoff from paddy fields serves as one of the main sources of water pollution. Our aim was to reduce N runoff from paddy fields by fertilizer management and inoculation with arbuscular mycorrhizal fungi（AMF）. In northeast China, Shuangcheng city in Heilongjiang province, a field experiment was conducted, using rice provided with 0%, 20%, 40%, 60%, 80%,and 100% of the local norm of fertilization（including N, phosphorus and potassium）, with or without inoculation with Glomus mosseae. The volume, concentrations of total N（TN）,dissolved N（DN） and particulate N（PN） of runoff water were measured. We found that the local norm of fertilization led to 18.9 kg/ha of N runoff during rice growing season, with DN accounting for 60%–70%. We also found that reduction in fertilization by 20% cut down TN runoff by 8.2% while AMF inoculation decreased N runoff at each fertilizer level and this effect was inhibited by high fertilization. The combination of inoculation with AMF and 80% of the local norm of fertilization was observed to reduce N runoff by 27.2%. Conclusively, we suggested that the contribution of AMF inoculation combined with decreasing fertilization should get more attention to slow down water eutrophication by reducing N runoff from paddy fields.

Effects of tillage on soil nitrogen and its components from rice-wheat fields in subtropical regions of China

It is of great significance to explore the effects of different tillage practices on total nitrogen and its components in rice-wheat rotation farmland.The experiment was carried out in Jiangyan County,Jiangsu Province of China,and a total of four treatments were set up:minimum tillage(MT),rotary tillage(RT),conventional tillage(CT),and conventional tillage without straw retention(CT0).The total nitrogen(TN),light fraction nitrogen(LFN),heavy fraction nitrogen(HFN),particulate nitrogen(PN),and mineral-associated nitrogen(MN)in 0-20 cm soil were determined.The results show that MT increased TN concentration by2.26%-27.57%compared with the other treatments in 0-5 cm soil,but it lost this advantage in 5-10 cm and 10-20 cm soil.MT altered the concentration of LFN by 6.03%-95.86%,of HFN by 1.68%-20.75%,of PN by 12.58%-96.83%,and of MN by−1.73%-9.83%as compared to RT,CT,and CT0 in 0-5 cm soil,respectively.With the deepened of soil depth,the concentration of TN,LFN,HFN,PN,and MN decreased quickly in MT,which was lower than that in RT and CT at 10-20 cm soil depth.Straw return increased the concentration of TN and its components in 0-20 cm soil.The concentration of TN was extremely significantly positively correlated with that of LFN,HFN,PN,and MN(p<0.01).The variation of TN was significantly positively correlated with that of LFN,HFN,PN,and MN(p<0.01),and LFN showed the highest sensitivity to tillage practice.In general,minimum tillage combined with straw retention increased the concentration of soil TN and its components in topsoil.LFN was the best indicator to indicate the change in soil total nitrogen affected by tillage practice.

High NO_2/NO_X emissions downstream of the catalytic diesel particulate filter:An influencing factor study

Diesel vehicles are responsible for most of the traffic-related nitrogen oxide（NO x） emissions,including nitric oxide（NO） and nitrogen dioxide（NO2）. The use of after-treatment devices increases the risk of high NO2/NO x emissions from diesel engines. In order to investigate the factors influencing NO2/NO x emissions, an emission experiment was carried out on a high pressure common-rail, turbocharged diesel engine with a catalytic diesel particulate filter（CDPF）. NO2 was measured by a non-dispersive ultraviolet analyzer with raw exhaust sampling. The experimental results show that the NO2/NO x ratios downstream of the CDPF range around 20%–83%, which are significantly higher than those upstream of the CDPF. The exhaust temperature is a decisive factor influencing the NO2/NO x emissions. The maximum NO2/NO x emission appears at the exhaust temperature of 350°C. The space velocity,engine-out PM/NO x ratio（mass based） and CO conversion ratio are secondary factors. At a constant exhaust temperature, the NO2/NO x emissions decreased with increasing space velocity and engine-out PM/NO x ratio. When the CO conversion ratios range from 80% to 90%,the NO2/NO x emissions remain at a high level.