[Analysis of HONO Concentration and Source in Typical Rural Area of North China].

Nitrous acid (HONO) is easily photolyzed with the production of·OH, which plays an important role in the formation of regional secondary pollution. In China, research of HONO observation is concentrated mainly in urban areas and is rarely reported in rural areas. In our study, a one-month HONO field observation was conducted at the Station of Rural Environment, Chinese Academy of Sciences (Dongbaituo Village, Wangdu County, Hebei Province) in November 2017 using the long path absorption photo meter (LOPAP). The concentration, variety characteristics, and budget of HONO was studied. During the observation period, HONO exhibited pronounced diurnal variation with low concentrations in the day and high concentration in the evening. The highest concentration at night was about 3.70×10-9, and the lowest concentration at noon was about 0.10×10-9, indicating the presence of a strong source of HONO in rural areas. The CO concentration increased significantly before and after heating, whereas the HONO concentration did not change significantly, indicating that heating combustion contributed less to HONO, Direct emission of motor vehicles at night contributed 23.20% and 31.20% to HONO in polluted and clean weather conditions, respectively, indicating the presence of strong sources of HONO in polluted weather conditions. The average formation rate of HONO at night from homogeneous reaction of·OH and NO could reach 0.40×10-9 h-1, which is 0.67 times higher than that of heterogeneous reaction of NO2 (0.24×10-9 h-1), indicating that the homogeneous reaction of·OH and NO is the main source of HONO at night. HONO has a strong unknown source in the daytime with an intensity reaching 1.37×10-9 h-1, which contributes about 50% to HONO.

[N2O exchange fluxes from wheat-maize crop rotation system in the North China Plain].

N2O exchange fluxes from the intensively cultivated winter wheat-summer maize crop rotation system in the North China Plain were measured by the static chamber technique under normal fertilization treatment and normal fertilization combined with straw returning treatment. The results indicated that the cumulative emissions of N2O from normal fertilization treatment and normal fertilization combined with straw returning treatment were 7.61 kg x hm(-2) and 12.6 kg x hm(-2), respectively. The increased N2O from the straw returning mainly occurred during the maize growing season. The N2O emission during the maize growing season from the two fertilization treatments accounted for 57% - 86% of the annual N2O cumulative emission, which indicated that the annual emission of N2O mainly occurred during the maize growing season. Total N2O emission after 10 days of each fertilization accounted for about 71% - 88% of the annual emission. It is obvious that the application of existing chemical fertilizers greatly promoted the N2O emissions in the North China Plain.

Effect of pyrene on denitrification activity and abundance and composition of denitrifying community in an agricultural soil.

Toxicity of pyrene on the denitrifiers was studied by spiking an agricultural soil with pyrene to a series of concentrations (0-500 mg kg(-1)) followed by dose-response and dynamic incubation experiments. Results showed a positive correlation between potential denitrification activity and copy numbers of denitrifying functional genes (nirK, nirS and nosZ), and were both negatively correlated with pyrene concentrations. Based on the comparison of EC(50) values, denitrifiers harboring nirK, nirS or nosZ gene were more sensitive than denitrification activity, and denitrifiers harboring nirS gene were more sensitive than that harboring nirK or nosZ genes. Seven days after spiking with EC(50) concentration of pyrene, denitrifiers diversity decreased and community composition changed in comparison with the control. Phylogenetic analyses of three genes showed that the addition of pyrene increased the proportion of Bradyrhizobiaceae, Rhodospirillales, Burkholderiales and Pseudomonadales. Some species belonging to these groups were reported to be able to degrade PAHs.

[Measurement of near-UV absorption cross sections of CS2].

The UV-absorption cross sections of CS2 are reported. The absorption spectra were measured by using a diode array spectrometer over the wavelength range of 220-380 nm at room temperature (298 +/- 3)K. The maximum absorption cross section appeared around 315 nm with the value of sigma (315 nm) = 7.184 x 10(-20) cm2 x molecule(-1). The measured data by this study were in good agreement with that reported in the literature, and used to estimate the photolysis of the CS2 in the atmosphere.

[Contribution of isoprene emitted from vegetable to atmospheric formaldehyde in the ambient air of Beijing city].

Methacrolein (MACR) and methyl vinyl ketone (MVK), which are the characteristic products of isoprene photooxidation in the atmosphere, as well as formaldehyde, were determined during March to November of 2006 in the ambient air of Beijing city. Cartridges coated with 2, 4-dinitrophenylhenylhydrazine (DNPH) were used to collect those carbonyls in ambient air and a high pressure liquid chromatography (HPLC) was used for quantification. Distinct amounts of MACR and MVK were detected during vegetable growing seasons from April to October with ambient levels in ranges of 0.11 x 10(-9) - 0.67 x 10(-9) and 0.19 x 10(-9) - 1.36 x 10(-9), respectively, with their maximal concentrations appearing in August. MACR and MVK were measured under the detecting limit in March and November, which may be ascribed to low isoprene emission from the broadleaf trees without leaves during two months. According to the stoichiometric coefficients among MVK, MACR, isoprene and formaldehyde, the concentrations of the reacted isoprene due to photo-oxidation can be calculated derived from the concentrations of the measured MVK and MACR. Then, the monthly (April to October) average concentrations of formaldehyde produced by the photo-oxidation of reacted isoprene were roughly estimated to be in the range of 0.35 x 10(-9) - 2.5 x 10(-9), which accounted for 4.6%-11.5% of total atmospheric formaldehyde. During the period with active atmospheric photo-oxidation (June to August), the contribution of biogenic isoprene to formaldehyde was predominant. Therefore, the biogenic isoprene is an important source to local photo-oxidant formation in Beijing and should be considered of.

Temperature dependence of the absolute rate constant for the reaction of ozone with dimethyl sulfide.

Absolute rate constants for the reaction of ozone with dimethyl sulfide (DMS) were measured in a 200-L Teflon chamber over the temperature range of 283-353 K. Measurements were carried out using DMS in large excess over ozone of 10 to 1 or greater. Over the indicated temperature range, the data could be fit to the simple Arrhenius expression as kDMS = (9.96 +/- 3.61) x 10(-11) exp (-(7309.7 +/- 1098.2)/T) cm3/(molecule x s). A compared investigation of the reaction between ozone and ethene had a kC2H4 value of (1.35 +/- 0.11) x 10(-18) cm3/(molecule x s) at room temperature.

[Methane emission from aquatic vegetation zones of Wuliangsu Lake, Inner Mongolia].

To quantify the variations of methane fluxes from different aquatic vegetation zones, two-year measurements were measured at different aquatic vegetation zones and water depths using static chamber technique during two growing season from April to October in 2003 and 2004. Results showed that the average emission flux of CH4 from Potamogeton pectinatus (submerged macrophyte) growing zones was (3.44 +/- 1.60) mg x (m2 x h)(-1), 78.06% lower than that from Phragmites australis (emergent macrophyte). Significant seasonal and diurnal variations of CH4 emission were observed for Phragmites community; however, the variations were minor for P. pectinatus. Sediment temperature at 5 cm and photosynthesis active radiation were important factors influencing seasonal and diurnal variations of CH4 fluxes from Phragmites zone. Annual methane flux from the lake was 1 024.6 t and 1 156.7 t in 2003 and 2004, respectively.

Surface-exchange of NOx and NH3 above a winter wheat field in the Yangtze Delta, China.

A four-dynamic-chamber system was constructed to measure NOx and NH3 surface-exchange between a typical wheat field and the atmosphere in the Yangtze Delta, China. The average fluxes ofNO, NO2 and NH3 were 79, -5.6 and -5.1 ngN/(m2 x s), and 91, -1.8 and 23 ngN/(m2 x s), respectively for the wheat field and the bare soil. The NO flux was positively correlated with soil temperature and the fluxes of NO2 and NH3 were negatively correlated with their ambient concentrations during the investigated period. The compensation point of NO2 between the wheat field and the atmosphere was 11.9 microg/m3. The emissions of NO-N and NH3-N from the urea applied to the wheat field were 2.3% and 0.2%, respectively, which indicated that the main pathway of N loss from the investigated winter wheat field was NO. Application of a mixture of urea and lignin increased the emissions of NO, but also greatly increased the yield of the winter wheat.

Vertical distributions of COS and CS2 in Beijing City.

Vertical distributions of COS and CS2 were measured at a meteorological tower in Beijing City. The mixing ratios of COS and CS2 are in the range of 371-1681 pptv and 246-1222 pptv, respectively. The significant high mixing ratios of the two compounds at ground level and distinct vertical distributions indicated the existence of strong anthropogenic sources of COS and CS2 in Beijing City. Domestic stoves and central heaters are important sources of COS during winter season. Cesspools may play significant role on COS over whole seasons. Chemical productions may be responsible for the observed high mixing ratios of CS2 in Beijing City.