模拟氮沉降对温带阔叶红松林地氮素净矿化量的影响

采用埋置PVC管的树脂芯方法原位测定了不同氮形态及其剂量作用下长白山阔叶红松林地0～7 cm和0～15 cm土壤氮素净氨化、净硝化和净矿化量的季节和年际变化规律.近3年的观测结果表明,对照处理不同土层氮素年净矿化量中以净氨化占主导地位,约占净矿化量的53％～72％,高剂量NO3-N的输入使该比例减少至37％～66％,而NH4-N的输入却使该比例增至86％～92％.随着模拟氮沉降量增加,土壤氮素年净矿化量也随之增加,尤其外源NH+4-N输入对净矿化量的促进作用更为明显,但随着施肥年限的延长,这种促进作用逐渐减弱.与林地0～15 cm土壤相比,氮沉降量增加对0～7 cm土壤氮素净氨化和净矿化量的促进作用更为明显,尤其是NH4Cl处理的促进作用更大.通过将实验结果与前人报道的野外原位观测整合,逐步回归分析后发现土壤氮素年净矿化量随着氮素年沉降量的增加而增大,氮沉降量对不同区域森林土壤氮素年净矿化量的贡献率约为38％;大气氮沉降量、森林有机层pH及其碳/氮比值可解释不同区域森林表层土壤氮素年净矿化量一半的变化.研究结果将利于有效预测区域林地氮素净矿化量特征及其对环境变化的响应.     

Atmospheric inorganic nitrogen in marine aerosol and precipitation and its deposition to the North and South Pacific Oceans

Aerosol and rain samples were collected between 48°N and 55°S during the KH-08-2 and MR08-06 cruises conducted over the North and South Pacific Ocean in 2008 and 2009, to estimate dry and wet deposition fluxes of atmospheric inorganic nitrogen (N). Inorganic N in aerosols was composed of ~68% NH₄⁺ and ~32% NO₃^– (median values for all data), with ~81% and ~45% of each species being present on fine mode aerosol, respectively. Concentrations of NH₄⁺ and NO₃⁻ in rainwater ranged from 1.7–55 μmol L⁻¹ and 0.16–18 μmol L⁻¹, respectively, accounting for ~87% by NH₄⁺ and ~13% by NO₃⁻ of total inorganic N (median values for all data). A significant correlation (r = 0.74, p < 0.05, n = 10) between NH₄⁺ and methanesulfonic acid (MSA) was found in rainwater samples collected over the South Pacific, whereas no significant correlations were found between NH₄⁺ and MSA in rainwater collected over the subarctic (r = 0.42, p > 0.1, n = 6) and subtropical (r = 0.33, p > 0.5, n = 6) western North Pacific, suggesting that emissions of ammonia (NH₃) by marine biological activity from the ocean could become a significant source of NH₄⁺ over the South Pacific. While NO₃⁻ was the dominant inorganic N species in dry deposition, inorganic N supplied to surface waters by wet deposition was predominantly by NH₄⁺ (42–99% of the wet deposition fluxes for total inorganic N). We estimated mean total (dry + wet) deposition fluxes of atmospheric total inorganic N in the Pacific Ocean to be 32–64 μmol m⁻² d⁻¹, with 66–99% of this by wet deposition, indicating that wet deposition plays a more important role in the supply of atmospheric inorganic N than dry deposition.     

Aspects of the cycle of inorganic nitrogen compounds in the tropical rain forest of the Ivory Coast

A partial balance of mineral N is given for the basins of two coastal rivers in a forest zone in the Ivory Coast. The dry and wet depositions on the basin surfaces is given for particulate matter (NO₃ ^–, NH₄ ⁺). The quantity of mineral N washed away in the rivers is evaluated. The losses from leaching of the soils by rainwater are about 0.33 to 1.0% of the atmospheric depositions for NH₄ ⁺–N and 2.2 to 5.8% for NO₃ ^––N. The yearly atmospheric input of N compounds to the ecosystem, about 1.4 g N m^–2 y^–1, is at least 14% of mineral N formed in the soils and is therefore quite significant.     

Seasonal variation of volatile organic iodine compounds in the water column of Funka Bay,Hokkaido, Japan

Volatile organic iodine compounds (VOIs) emitted from the ocean surface to the air play an important role in atmospheric chemistry. Shipboard observations were conducted in Funka Bay, Hokkaido, Japan, bimonthly or monthly from March 2012 to December 2014, to elucidate the seasonal variations of VOI concentrations in seawater and their sea-to-air iodine fluxes. The bay water exchanges with the open ocean water of the North Pacific twice a year (early spring and autumn). Vertical profiles of CH₂I₂, CH₂ClI, CH₃I, and C₂H₅I concentrations in the bay water were measured bimonthly or monthly within an identified water mass. The VOI concentrations began to increase after early April at the end of the diatom spring bloom, and represented substantial peaks in June or July. The temporal variation of the C₂H₅I profile, which showed a distinct peak in the bottom layer from April to July, was similar to the PO₄ ^3? variation profile. Correlation between C₂H₅I and PO₄ ^3? concentrations (r = 0.93) suggests that C₂H₅I production was associated with degradation of organic matter deposited on the bottom after the spring bloom. CH₂I₂ and CH₂ClI concentrations increased substantially in the surface and subsurface layers (0–60 m) in June or July resulted in a clear seasonal variation of the sea-to-air iodine flux of the VOIs (high in summer or autumn and low in spring).     

Rainwater Chemistry and Wet Deposition over the Wet Savanna Ecosystem of Lamto (Côte d'Ivoire)

From the IGAC-DEBITS Africa network (IDAF), data sets on precipitation chemistry collected from the ‘wet savanna ecosystem’ site of Lamto (Côte d'Ivoire), are analyzed (1995–2002). Inorganic (Ca^{2 +}, Mg^{2 +}, Na⁺, K⁺, NH₄ ⁺, Cl^?, SO₄ ^{2 ?}, NO₃ ^?) and organic (HCOO^?, CH₃COO^?) ions content were determined using Ion Chromatography. The analyzed 631 rainfall events represent 8420.9 mm of rainfall from a 9631.1 mm total. The precipitation chemistry at Lamto is influenced by four main sources: natural biogenic emissions from savanna soils (NO _x and NH₃), biomass burning (savanna and domestic fires), terrigeneous particles emissions from dry savanna soils, and marine compounds embedded in the summer monsoon. The inter-annual variability of the weighted volume mean concentration of chemical species linked with wet deposition fluctuates by ～ 20% over the period. Ammonium concentration is found to be the highest (17.6 μ eq.l^{? 1}) from all IDAF sites belonging to the West Africa ecosystems. Ammonia sources are from domestic animals, fertilizers and biomass burning. In spite of the high potential acidity of 30.5 μ eq.l^{? 1} from NO₃ ^?, SO₄ ^{2 ?}, HCOO^? and CH₃COO^?, a relatively weak acidity is measured: 6.9 μ eq.l^{? 1}. The 40% acid neutralization is explained by the acid gas – alkaline soil particles interaction. The remaining neutralization is from inclusion of gaseous ammonia. When results from Lamto, are compared with those from Banizoumbou (dry savanna) and Zoetele (equatorial forest), a regional view for wet tropospheric chemistry processes is obtained. The high concentration of the particulate phase in precipitation emphasizes the importance of multiphases processes between gases and particles in the atmospheric chemistry of the West Africa ecosystems. For example, the nss Ca^{2 +} precipitation content, main indicator of terrigeneous particles, goes from 30.8 μ eq.l^{? 1} in dry savanna to 9.2 μ eq.l^{? 1} at Lamto and 8.9 μ eq.l^{? 1} in the Cameroon forest. A similar gradient is obtained for rainfall mineral particles precipitation content with contribution of 80% in dry savanna, 40% in wet savanna, and 20% in the equatorial forest.     

Production of N2O,CH4, and CO2 from soils in the tropical savanna during the dry season

Emissions of N₂O, CH₄, and CO₂ from soils at two sites in the tropical savanna of central Venezuela were determined during the dry season in February 1987. Measured arithmetic mean fluxes of N₂O, CH₄, and CO₂ from undisturbed soil plots to the atmosphere were 2.5×10⁹, 4.3×10¹⁰, and 3.0×10¹³ molecules cm^-2 s^-1, respectively. These fluxes were not significantly affected by burning the grass layer. Emissions of N₂O increased fourfold after simulated rainfall, suggesting that production of N₂O in savanna soils during the rainy season may be an important source for atmospheric N₂O. The CH₄ flux measurements indicate that these savanna soils were not a sink, but a small source, for atmospheric methane. Fluxes of CO₂ from savanna soils increased ninefold two hours after simulated rainfall, and remained three times higher than normal after 16 hours. More research is needed to clarify the significance of savannas in the global cycles of N₂O, CH₄, CO₂, and other trace gases, especially during the rainy season.     

Size distributions and dry deposition fluxes of water-soluble inorganic nitrogen in atmospheric aerosols in Xiamen Bay,China

Size-segregated aerosol particles were collected using a high volume MOUDI sampler at a coastal urban site in Xiamen Bay, China, from March 2018 to June 2020 to examine the seasonal characteristics of aerosol and water-soluble inorganic ions (WSIIs) and the dry deposition of nitrogen species. During the study period, the annual average concentrations of PM₁, PM_2.5, PM₁₀, and TSP were 14.8?±?5.6, 21.1?±?9.0, 35.4?±?14.2 μg m^?3, and 45.2?±?21.3 μg m^?3, respectively. The seasonal variations of aerosol concentrations were impacted by the monsoon with the lowest value in summer and the higher values in other seasons. For WSIIs, the annual average concentrations were 6.3?±?3.3, 2.1?±?1.2, 3.3?±?1.5, and 1.6?±?0.8 μg m^?3 in PM₁, PM_1-2.5, PM_2.5–10, and PM_>10, respectively. In addition, pronounced seasonal variations of WSIIs in PM₁ and PM_1-2.5 were observed, with the highest concentration in spring-winter and the lowest in summer. The size distribution showed that SO₄^2?, NH₄⁺ and K⁺ were consistently present in the submicron particles while Ca²⁺, Mg²⁺, Na⁺ and Cl^? mainly accumulated in the size range of 2.5–10 μm, reflecting their different dominant sources. In spring, fall and winter, a bimodal distribution of NO₃^? was observed with one peak at 2.5–10 μm and another peak at 0.44–1 μm. In summer, however, the fine mode peak disappeared, likely due to the unfavorable conditions for the formation of NH₄NO₃. For NH₄⁺ and SO₄^2?, their dominant peak at 0.25–0.44 μm in summer and fall shifted to 0.44–1 μm in spring and winter. Although the concentration of NO₃–N was lower than NH₄–N, the dry deposition flux of NO₃–N (35.77?±?24.49 μmol N m^?2 d^?1) was much higher than that of NH₄–N (10.95?±?11.89 μmol N m^?2 d^?1), mainly due to the larger deposition velocities of NO₃–N. The contribution of sea-salt particles to the total particulate inorganic N deposition was estimated to be 23.9—52.8%. Dry deposition of particulate inorganic N accounted for 0.95% of other terrestrial N influxes. The annual total N deposition can create a new productivity of 3.55 mgC m^?2 d^?1, accounting for 1.3–4.7% of the primary productivity in Xiamen Bay. In light of these results, atmospheric N deposition could have a significant influence on biogeochemistry cycle of nutrients with respect to projected increase of anthropogenic emissions from mobile sources in coastal region.

     

Ion fluxes from fog and rain to an agricultural and a forest ecosystem in Europe

The deposition fluxes of inorganic compounds dissolved in fog and rain were quantified for two different ecosystems in Europe. The fogwater deposition fluxes were measured by employing the eddy covariance method. The site in Switzerland that lies within an agricultural area surrounded by the Jura mountains and the Alps is often exposed to radiation fog. At the German mountain forest ecosystem, on the other hand, advection fog occurs most frequently. At the Swiss site, fogwater deposition fluxes of the dominant components SO₄²⁻ (0.027 mg S m⁻² day⁻¹), NO₃⁻ (0.030 mg N m⁻² day⁻¹) and NH₄⁺ (0.060 mg N m⁻² day⁻¹) were estimated to be <5% of the measured wet deposition (0.85, 0.70 and 1.34 mg m⁻² day⁻¹, respectively). The corresponding fluxes at the forest site (0.62, 0.82 and 1.16 mg m⁻² day⁻¹, respectively) were of the same order of magnitude as wet deposition (1.04, 1.01 and 1.36 mg m⁻² day⁻¹), illustrating the importance of fog (or occult) deposition. Trajectory analyses at the forest site indicate significantly higher fogwater concentrations of all major ions if air originated from the east (i.e. the Czech Republic), which is in close agreement with earlier studies.     

Precipitation Chemistry and Wet Deposition in Kruger National Park, South Africa

The chemical composition, as well as the sources contributing to rainwater chemistry have been determined at Skukuza, in the Kruger National Park, South Africa. Major inorganic and organic ions were determined in 93 rainwater samples collected using an automated wet-only sampler from July 1999 to June 2002. The results indicate that the rain is acidic and the averaged precipitation pH was 4.72. This acidity results from a mixture of mineral acids (82%, of which 50% is H₂SO₄) and organic acids (18%). Most of the H₂SO₄ component can be attributed to the emissions of sulphur dioxide from the industrial region on the Highveld. The wet deposition of S and N is 5.9 kgS⋅ha⁻¹⋅yr⁻¹ and 2.8 kgN⋅ha⁻¹⋅yr⁻¹, respectively. The N deposition was mainly in the form of NH₄ ⁺. Terrigenous, sea salt component, nitrogenous and anthropogenic pollutants have been identified as potential sources of chemical components in rainwater. The results are compared to observations from other African regions.     

Effects of Irrigation on Nitrous Oxide, Methane and Carbon Dioxide Fluxes in an Inner Mongolian Steppe

Increased precipitation during the vegetation periods was observed in and further predicted for Inner Mongolia. The changes in the associated soil moisture may affect the biosphere-atmosphere exchange of greenhouse gases. Therefore, we set up an irrigation experiment with one watered （W） and one unwatered plot （UW） at a winter-grazed Leymus chinensis-steppe site in the Xilin River catchment, Inner Mongolia. UW only received the natural precipitation of 2005 （129 mm）, whereas W was additionally watered after the precipitation data of 1998 （in total 427 mm）. In the 3-hour resolution, we determined nitrous oxide （N20）, methane （CH4） and carbon dioxide （CO2） fluxes at both plots between May and September 2005, using a fully automated, chamber-based measuring system. N20 fluxes in the steppe were very low, with mean emissions （±s.e.） of 0.9-4-0.5 and 0.7-4-0.5 μg N m^-2 h^-1 at W and UW, respectively. The steppe soil always served as a CH4 sink, with mean fluxes of -24.1-4-3.9 and -31.1-4- 5.3 μg C m^-2 h^-1 at W and UW. Nighttime mean CO2 emissions were 82.6±8.7 and 26.3±1.7 mg C m^-2 h^-1 at W and UW, respectively, coinciding with an almost doubled aboveground plant biomass at W. Our results indicate that the ecosystem CO2 respiration responded sensitively to increased water input during the vegetation period, whereas the effects on CH4 and N2O fluxes were weak, most likely due to the high evapotranspiration and the lack of substrate for N2O producing processes. Based on our results, we hypothesize that with the gradual increase of summertime precipitation in Inner Mongolia, ecosystem CO2 respiration will be enhanced and CH4 uptake by the steppe soils will be lightly inhibited.     

The effects of below-cloud aerosol on the acidification process of rain

Using a model of the acidification process of rain, we calculate and analyze the effects and contributions of a below-cloud aerosol in its different concentrations and acidities on the pH and ion components of rain (SO ₄ ^2– , H⁺, NO ₃ ^– , NH ₄ ⁺ , etc.) under the conditions of different concentrations of pollution gases. The results show that the aerosol has an acidification or alkalization effect on the rain which changes the pHs of rain and aerosol. As acidifying pollution gas concentrations (SO₂, HNO₃) are low, the acid aerosol has important effects on the pH and H⁺ of rain, but as the gas concentrations are high, the acid aerosol has very little effect. The alkalizing aerosol makes the pH of rain increase by between 0.3 and 0.5 and neutralizes about 60% of H⁺ in the rain. As alkalizing pollution gas NH₃ exists, the acid aerosol has important effects on the pH and H⁺ of rain. But the alkalizing aerosol has very little effect, especially as the NH₃ concentration is high. The percentage contribution of the aerosol to SO ₄ ^2– in rain is generally 7–15%, the contribution of the aerosol to NO ₃ ^– is nearly the same as that of HNO₃=1 ppb, and the contribution of the aerosol to NH ₄ ⁺ is nearly the same as that of NH₃, from 5 to 7 ppb, and is an important source of NH ₄ ⁺ in rain. Finally, according to the actual conditions of typical regions in the south and north of China (Chongqing and Beijing), we analyze the effects of aerosol and pollution gases on the ion components of rain.     

Rainwater chemistry and bulk atmospheric deposition in a tropical semiarid ecosystem: the Brazilian Caatinga

We assessed the rainwater chemistry, the potential sources of its main inorganic components and bulk atmospheric deposition in a rural tropical semiarid region in the Brazilian Caatinga. Rainfall samples were collected during two wet seasons, one during an extremely dry year (2012) and one during a year with normal rainfall (2013). According to measurements of the main inorganic ions in the rainwater (H⁺, Na⁺, NH₄ ⁺, K⁺, Ca²⁺, Mg²⁺, Cl^?, NO₃ ^?, and SO₄ ^2?), no differences were observed in the total ionic charge between the two investigated wet seasons. However, Ca²⁺, K⁺, NH₄ ⁺ and NO₃ ^? were significant higher in the wetter year (p < 0.05) which was attributed to anthropogenic activities, such as organic fertilizer applications. The total ionic contents of the rainwater suggested a dominant marine contribution, accounting for 76 % and 58 % of the rainwater in 2012 and 2013, respectively. The sum of the non-sea-salt fractions of Cl^?, SO₄ ^2?, Mg²⁺, Ca²⁺ and K⁺ were 19 % and 33 % in 2012 and 2013, and the nitrogenous compounds accounted for 2.8 % and 6.0 % of the total ionic contents in 2012 and 2013, respectively. The ionic ratios suggested that Mg²⁺ was probably the main neutralizing constituent of rainwater acidity, followed by Ca²⁺. We observed a low bulk atmospheric deposition of all major rainwater ions during both wet seasons. Regarding nitrogen deposition, we estimated slightly lower annual inputs than previous global estimates. Our findings contribute to the understanding of rainfall chemistry in northeastern Brazil by providing baseline information for a previously unstudied tropical semiarid ecosystem.     

Comparison of collection methods to determine atmospheric deposition in a rural Mediterranean site (NE Spain)

Wet-only, dry-only, bulk deposition and deposition of sedimentary particles and gases deposited after the last rain (DAR) were collected weekly at La Castanya station in the Montseny mountains (NE Spain, 41°46′N, 2°21′E) from February 2009 to July 2010. These samples were analysed for pH, alkalinity, and the concentrations of major ions (Cl^?, NO₃ ^?, SO₄ ^2?, Na⁺, K⁺, Ca²⁺, Mg²⁺, NH₄ ⁺). Significant differences were observed between bulk and wet-only precipitation, with an enrichment of ions associated to coarse particles in bulk deposition. The comparison between wet and dry fluxes revealed that the removal of compounds at Montseny occurred mainly by wet deposition, which accounted for 74 % of total deposition. The dry flux was characterised by the predominance of K⁺, Ca²⁺ and Mg²⁺, which are related to coarse particles. Bulk collection methods at Montseny were considered representative of total atmospheric deposition, since bulk deposition plus DAR accounted for 97 % of total deposition measured with wet and dry-only collection devices. Thus, bulk deposition collectors can be recommended for deposition networks at remote sites (lacking electricity connection) in environments, where coarse particles are a predominant fraction of the aerosol mass.     

Methodology of analysis associating survey results by the filter-pack method with those of precipitation- Acid-base balance on acid-related and alkali-related chemical species in urban ambient air and its influence on the acidification of precipitation -

Continuous weekly monitoring on the concentration of gases and aerosols in urban ambient air by a four-stage filter-pack method was carried out for 7 years in order to study not only the acid-base balance of acid-related (HNO₃, NO₃ ⁻, and non-sea-salt-(nss-)SO₄ ²⁻) and alkali-related (NH₃, NH₄ ⁺, and nss-Ca²⁺) chemical species but also its influence on the acidification of precipitation. The concentrations of the total nitrate (= NO₃⁻ + HNO₃) and nss-SO₄²⁻ showed a similar seasonal variation: high in the summer and low in the winter. The total nitrate and nss-SO₄²⁻ accounted for 0.43 and 0.57 of the acid-related species, respectively, on an equivalent basis. The total ammonium (= NH₃ + NH₄⁺) accounted for more than 0.9 of the alkali-related species, except for a springtime nss-Ca²⁺ episodic peak. The alkali-related species were generally overabundant compared with the acid-related species in the HNO₃-NO₃⁻-nss-SO₄²⁻-NH₃-NH₄⁺-nss-Ca²⁺ system. The alkali-rich distribution was especially pronounced in the winter, but the acid-related species was comparable to the alkali-related species in the summer, which was attributed to the larger H⁺ deposition by precipitation in the summer. This study can provide a methodology to associate survey results obtained by a filter-pack method with those of precipitation.     

Catalysed self-cleaning of air on the earth's surface

Generally, it is assumed that UV-light, high temperature or reactive molecules like O₃ and OH are needed to activate gas reactions in air. In consequence, the catalytic activity on natural materials such as sand and soil on the earth's surface is assumed to be insignificant. We have measured O₂-dissociation rates on natural quartz sand at 40˚C and compared these with O₂-dissociation rates near 500˚C on materials with well-known catalytic activity. In terms of probabilities for dissociation of impinging O₂-molecules the measured rates are in the 10⁻¹²–10⁻⁴ range. We have also measured dissociation rates of H₂ and N₂, water-formation from H₂ and O₂ mixtures, exchange of N between N₂, NO _x and a breakdown of HNO₃, NO₂ and CH₄ on natural quartz sand at 40˚C. The measured rates together with an effective global land area have been used to estimate the impact of thermodynamically driven reactions on the earth's surface on the global atmospheric budgets of H₂, NO₂ and CH₄. The experimental data on natural quartz sand together with data from equilibrium calculations of air suggest that an expected increase in anthropogenic supply of air pollutants, such as NO _x or other “reactive” nitrogen compounds, hydrogen and methane, will be counter-acted by catalysis on the earth's surface. On the other hand, at Polar Regions and boreal forests where the “reactive” nitrogen concentration is below equilibrium, the same catalytic effect activates formation of bio-available nitrogen compounds from N₂, O₂ and H₂O.     

Chemical and isotopic interpretation of major ion compositions from precipitation: a one-year temporal monitoring study in Wrocław,SW Poland

The chemical compositions (Na⁺, NH₄ ⁺, K⁺, Mg²⁺, Ca²⁺, Cl^?, NO₂ ^?, NO₃ ^?, SO₄ ^2?, HCO₃ ^?) of wet precipitation and nitrogen isotope compositions δ¹⁵N(NH₄ ⁺) were studied from January to December 2010 in Wroc?aw (SW Poland). Results of a principle component analysis show that 82 % of the data variability can be explained by three main factors: 1) F1 (40 %) observed during vegetative season (electrical conductivity, HCO₃ ^?, NO₃ ^?, NO₂ ^?, NH₄ ⁺ and SO₄ ^2?), mainly controlling rainwater mineralization; 2) F2 (26 %) observed during vegetative and heating seasons (K⁺, Ca²⁺ and Mg²⁺), probably representing a combination of two processes: anthropogenic dusts and fertilizers application in agricultural fields, and 3) F3 (16 %) reported mainly during heating season (Na⁺ and Cl^?) probably indicating the influence of marine aerosols. Variations of δ¹⁵N(NH₄ ⁺) from ?11.5 to 18.5?‰ identify three main pathways for the formation of NH₄ ⁺: 1) equilibrium fractionation between NH₃ and NH₄ ⁺; 2) kinetic exchange between NH₃ and NH₄ ⁺; 3) NH₄ ⁺ exchange between atmospheric salts particles and precipitation. The coupled chemical/statistical analysis and δ¹⁵N(NH₄ ⁺) approach shows that while fossil fuels burning is the main source of NH₄ ⁺ in precipitation during the heating season, during the vegetative season NH₄ ⁺ originates from local sewage irrigation fields in Osobowice or agricultural fertilizers.     

Estimates of global N2O emissions from cattle, pig and chicken manure, including a discussion of CH4 emissions

Humans seem to have doubled the global rate of terrestrial nitrogen fixation. Globally 50–70% (85 Tg, 1 Tg=10¹² g) of the nitrogen supplied in fertilizer (80 Tg N/a) and leguminous crops (40–80 Tg N/a) are used to feed cattle. The aim of the present study was to derive some estimates of global N₂O production from animal manure. As the parameter giving the most stable numerical basis for regional and global extrapolation we adopted the molar emission ratios of N₂O to NH₃. These ratios were measured in cattle, pig and chicken housings with different manure handling systems, in dung-heaps and in liquid manure storage tanks. Individual molar emission ratios from outside manure piles varied over two orders of magnitude, strongly dependent on the treatment of the manure. A median emission ratio of 1.6×10^-2 (n=65) was obtained in cow-sheds with slatted floors and liquid manure stored underneath and a median ratio of 24×10^-2 (n=31) was measured in a beef cattle housing with a solid manure handling system.We next extrapolated to global NH₃ emissions from those estimated for Europe, using N uptake by the animals as a scaling factor. Multiplication with observed N₂O to NH₃ ratios next provided some estimates of regional and global N₂O emissions. To account for the great variability of the emission ratios of N₂O/NH₃, we developed upper and lower case emission scenarios, based on lower and upper quartiles of measured emission ratios. The global emission from cattle and swine manure is in the range of 0.2–2.5 Tg N-N₂O/a, representing 44+-39% of the annual atmospheric accumulation rate. This N₂O emission arises from about 40 Tg N/a of cattle and pig manure stored in or at animal housings. We did not account for N₂O emissions from another 50 Tg N/a excreted by grazing cattle, goats and sheep, and application of the manure to agricultural fields. Our study makes it clear that major anthropogenic N₂O emissions may well arise from animal manure. The large uncertainty of emission ratios, which we encountered, show that much more intense research efforts are necessary to determine the factors that influence N₂O emissions from domestic animal manure both in order to derive a more reliable global estimate of N₂O release and to propose alternative waste treatment methods causing smaller N₂O releases. In our studies we found large enhancements in N₂O releases when straw was added to the manure, which is a rather common practice. In view of the ongoing discussion in Europe to re-install the traditional solid manure system (bed down cattle) for environmental and animal welfare reasons, it is noteworthy that our measurements indicate highest N₂O release from this particulary system.In a similar manner, but based on a smaller data set, we also estimated the release of CH₄ from cattle and swine manure and from liquid manure only to be about 9 Tg/year in good agreement with the estimate by the Environmental Protection Agency (1994) of 8.6+-2.6 Tg/year. A total annual methane release as high as 34 Tg/a was derived for solid and liquid cattle and pig manure from animals in housings.     

Ground Based Gas Phase Measurements in Surinam during the LBA-Claire 98 Experiment

As part of the LBA-CLAIRE-98 experiment, ground level atmosphericconcentrations of O₃, CO, hydroperoxides and organic acids weremeasured in the rainforest region in Surinam. Measurements of CO andO₃ were also made at a coastal site.The results suggest that a significant consumption of `boundary layer' ozoneoccurs over the forested region of Surinam, with an estimated net ozoneconsumption of about 5% hr^–1 during daytime. Thiswould be mainly explained by a low photochemical production and high drydeposition to the forest vegetation. Compared to other tropical sites, lowerlevels of H₂O₂ were observed at the rainforest site,with an average boundary layer concentration of 0.55± 0.2 nmolmol^–1. Also acetic and formic acids showed relatively lowaverage boundary layer mixing ratios; 1.1± 0.4 nmolmol^–1 and 1.4± 0.5 nmol mol^–1,respectively. Significant correlations were found between both acids andbetween the acids and hydrogen peroxide, suggesting an atmospheric source forthe acids.From the available observations we discuss possible implications of ourmeasurements for the O₃, HO₂, and NO_x budgetsand concentrations in the boundary layer. We conclude that, despite the highsolar irradiation, relatively low levels of O₃,H₂O₂, HCOOH and CH₃COOH are observed in theboundary layer of the rainforest of Surinam, probably due to low levels ofNO_x and high levels of VOCs, which leads to loss of OH andHO₂ radicals. Additionally, high deposition rates of these gasesoccur to the forest vegetation.     

Behaviour of H2O2, NH3, and black carbon in mixed-phase clouds during CIME

We investigated the partitioning of trace substances during the phase transition from supercooled to mixed-phase cloud induced by artificial seeding. Simultaneous determination of the concentrations of H₂O₂, NH₃ and black carbon (BC) in both condensed and interstitial phases with high time resolution showed that the three species undergo different behaviour in the presence of a mixture of ice crystals and supercooled droplets. Both H₂O₂ and NH₃ are efficiently scavenged by growing ice crystals, whereas BC stayed predominantly in the interstitial phase. In addition, the scavenging of H₂O₂ is driven by co-condensation with water vapour onto ice crystals while NH₃ uptake into the ice phase is more efficient than co-condensation alone. The high solubility of NH₄⁺ in the ice could explain this result. Finally, it appears that the H₂O₂–SO₂ reaction is very slow in the ice phase with respect to the liquid phase. Our results are directly applicable for clouds undergoing limited riming.     

Determination of heterogeneous reaction probability using deposition profile measurement in an annular reactor: Application to the N2O5/H2O reaction

A method for the estimation of the reaction probability of the heterogeneous N₂O₅+H₂O 2HNO₃ reaction using the deposition profile in a laminar flow tube, in which the walls are coated with the condensed aqueous phase of interest, is presented. The production of gas phase nitric acid on the surface followed by its absorption complicates the deposition profiles and hence the calculation of the reaction probability. An estimation of the branching ratio for this process enables a more appropriate calculation to be carried out. Reaction probabilities of N₂O₅ on substances including some normally constituting atmospheric aerosols, NaCl, NH₄HSO₄, as well as Na₂CO₃ are estimated and found to depend on relative humidity and characteristics of the coating used. These fell within the range (0.04–2.0)×10^–2.