ALBERT

Description: Nitrous acid (HONO) plays a significant role in the atmosphere, especially in the polluted troposphere. Its photolysis after sunrise is an important source of hydroxyl free radicals (OH). Measurements of nitrous acid and other pollutants were carried out in the Kathmandu urban atmosphere during January–February 2003, contributing to the sparse knowledge of nitrous acid in South Asia. The results showed average nocturnal levels of HONO (1.7±0.8 ppbv), NO2 (17.9±10.2 ppbv), and PM10 (0.18±0.11 mg m−3) in urban air in Kathmandu. Surprisingly high ratios of chemically formed secondary [HONO] to [NO2] (up to 30%) were found, which indicates unexpectedly efficient chemical conversion of NO2 to HONO in Kathmandu. The ratios of [HONO]/[NO2] at night were found to be much higher than previously reported values from measurements in urban air in Europe, North America and Asia. The influences of aerosol surface, ground reactive surface, and relative humidity on NO2-HONO chemical conversion were discussed. The high humidity, strong and low inversion layer at night, and high aerosol pollution burden in Kathmandu may explain the particularly efficient conversion of NO2 to HONO.

Description: Heterogeneous processes on dust particles are important for understanding the chemistry and radiative balance of the atmosphere. This paper investigates an intense Asian dust storm episode observed at Mount Heng (1269 m a.s.l.) in southern China on 24–26 April 2009. A set of aerosol and trace gas data collected during the study was analyzed to investigate their chemical evolution and heterogeneous photochemistry as the dust traveled to southern China. Results show that the mineral dust arriving at Mt. Heng experienced significant modifications during transport, with large enrichments in secondary species (sulfate, nitrate, and ammonium) compared with the dust composition collected at an upwind mountain top site (Mount Hua). A photochemical age "clock" (−Log10(NOx/NOy)) was employed to quantify the atmospheric processing time. The result indicates an obvious increase in the abundance of secondary water-soluble ions in dust particles with the air mass atmospheric processing time. Based on the observations, a 4-stage evolution process is proposed for carbonate-containing Asian dust, starting from fresh dust to particles coated with hydrophilic and acidic materials. Daytime-enhanced nitrite formation on the dust particles was also observed, which indicates the recent laboratory result of the TiO2 photocatalysis of NO2 as a potential source of nitrite and nitrous acid.

Description: Results from an intercomparison of several currently used in-situ techniques for the measurement of atmospheric formaldehyde (CH2O) are presented. The measurements were carried out at Bresso, an urban site in the periphery of Milan (Italy) as part of the FORMAT-I field campaign. Eight instruments were employed by six independent research groups using four different techniques: Differential Optical Absorption Spectroscopy (DOAS), Fourier Transform Infra Red (FTIR) interferometry, the fluorimetric Hantzsch reaction technique (five instruments) and a chromatographic technique employing C18-DNPH-cartridges (2,4-dinitrophenylhydrazine). White type multi-reflection systems were employed for the optical techniques in order to avoid spatial CH2O gradients and ensure the sampling of nearly the same air mass by all instruments. Between 23 and 31 July 2002, up to 13 ppbv of CH2O were observed. The concentrations lay well above the detection limits of all instruments. The formaldehyde concentrations determined with DOAS, FTIR and the Hantzsch instruments were found to agree within ±11%, with the exception of one Hantzsch instrument, which gave systematically higher values. The two hour integrated samples by DNPH yielded up to 25% lower concentrations than the data of the continuously measuring instruments averaged over the same time period. The consistency between the DOAS and the Hantzsch method was better than during previous intercomparisons in ambient air with slopes of the regression line not significantly differing from one. The differences between the individual Hantzsch instruments could be attributed in part to the calibration standards used. Possible systematic errors of the methods are discussed.

Description: Wetland loss and climate change are known to alter regional and global methane (CH4) budgets. Over the last six decades, an extensive area of marshland has been converted to cropland on the Sanjiang Plain in Northeast China, and a significant increase in air temperature has also been observed there, while the impacts on regional CH4 budgets remain uncertain. Through model simulation, we estimated the changes in CH4 emissions associated with the conversion of marshland to cropland and climate change in this area. Model simulations indicated a significant reduction of 1.1 Tg yr−1 from the 1950s to the 2000s in regional CH4 emissions. The cumulative reduction of CH4 from 1960 to 2009 was estimated to be ~36 Tg relative to the 1950s, and marshland conversion and the climate contributed 86 % and 14 % of this change, respectively. Interannual variation in precipitation (linear trend with P 〉 0.2) contributed to yearly fluctuations in CH4 emissions, but the relatively lower amount of precipitation over the period 1960–2009 (47 mm yr−1 lower on average than in the 1950s) contributed ~91 % of the reduction in the area-weighted CH4 flux. Global warming at a rate of 0.3 °C per decade (P 〈 0.001) has increased CH4 emissions significantly since the 1990s. Relative to the mean of the 1950s, the warming-induced increase in the CH4 flux has averaged 19 kg ha−1 yr−1 over the last two decades. For the RCP 2.6, RCP 4.5, RCP 6.0 and RCP 8.5 scenarios of the fifth IPCC assessment report (AR5), the CH4 flux is predicted to increase by 36 %, 52 %, 78 % and 95 %, respectively, by the 2080s compared to 1961–1990 in response to climate warming and wetting.

Description: Soil moisture plays a key role in vegetation restoration and ecosystem stability in arid and semiarid regions. The response of soil moisture to rainfall pulses is an important hydrological process, which is strongly influenced by land use during the implementation of vegetation restoration. In this study, vertical soil moisture variations of woodland (Pinus tabulaeformis), native grassland (Stipa bungeana), shrubland (Hippophea rhamnoides), cropland (Triticum aestivum) and artificial grassland (Onobrychis viciaefolia) in five soil profiles were monitored in a typical loess hilly area during the 2010 growing season. The results demonstrated that rainfall pulses directly affected soil moisture variation. A multi-peak pattern of soil moisture appeared during the growing season, notably in the surface soil layer. Meanwhile, the response of each vegetation type to rainfall was inconsistent, and a time-lag effect before reaching the peak value was detected, following each heavy rainfall event. The response duration of soil moisture, however, varied markedly with the size of rainfall events. Furthermore, higher soil water content was detected in grassland and shrubland. Woodland was characterized by relatively lower soil moisture values throughout the investigation period. Our research suggests that vegetation restoration efforts should give priority to grassland and shrubland at the research site. We suggest that more studies should be focused on the characteristics of community structure and spatial vegetation distribution on soil moisture dynamics, particularly within the grass and shrub ecosystems.

Description: Soil moisture plays a key role in vegetation restoration and ecosystem stability in arid and semiarid regions. The response of soil moisture to rainfall pulses is an important hydrological process, which is strongly influenced by land use during the implementation of vegetation restoration measures. In this study, vertical soil moisture variations of woodland (Pinus tabulaeformis), native grassland (Stipa bungeana), shrubland Hippophea rhamnoides), cropland (Triticum aestivum) and artificial grassland (Onobrychis viciaefolia) in five soil profiles were monitored in a typical loess hilly area during the 2010 growing season. The results demonstrated that rainfall pulses directly affected soil moisture variation. A multi-peak pattern of soil moisture appeared during the growing season, notably in the surface soil layer. Meanwhile, the response of each vegetation type to rainfall was inconsistent, and a time-lag effect before reaching the peak value was detected, following a heavy rainfall event. The response duration of soil moisture, however, varied markedly with the size of rainfall events. Furthermore, higher soil water content was detected in grassland and shrubland. Woodland was characterized by relatively lower soil moisture values throughout the investigation period. Our research suggests that vegetation restoration efforts should give priority to grassland and shrubland at the research site. We suggest that more studies should be focused on the characteristics of community structure and spatial vegetation distribution on soil moisture dynamics, particularly within the grass and shrub ecosystems.

Description: The Gonghe Basin is a sandified and desertified region of China, but the distribution of soil organic carbon (SOC) and total nitrogen (TN) along the cultivation chronosequence across this ecologically fragile region is not well understood. This study was carried out to understand the effects of restoration with Salix cheilophila for different periods of time (6, 11, 16, 21 years) to test whether it enhanced C and N storage. Soil samples, in four replications from seven depth increments (0–10, 10–20, 20–30, 30–50, 50–100, 100–150 and 150–200 cm), were collected in each stand. Soil bulk density, SOC, TN, aboveground biomass and root biomass were measured. Results indicated that changes occurred in both the upper and deeper soil layers with an increase in revegetation time. The 0–200 cm soil showed that the 6-year stand gained 3.89 Mg C ha−1 and 1.00 Mg N ha−1, which accounted for 40.82% of the original SOC and 11.06% of the TN of the 0-year stand. The 11-year stand gained 7.82 Mg C ha−1 and 1.98 Mg N ha−1 in the 0–200 cm soil layers, accounting for 58.06% of the SOC and 19.80% of the TN of the 0-year stand. The 16-year stand gained 11.32 Mg C ha−1 and 3.30 Mg N ha−1 in the 0–200 cm soil layers, accounting for 66.71% of the SOC and 21.98% of the TN of the 0-year stand. The 21-year stand gained 13.05 Mg C ha−1 and 5.45 Mg N ha−1 from the same soil depth, accounting for 69.79% of the SOC and 40.47% of the TN compared with the 0-year stand. The extent of these changes depended on soil depth and plantation age. The results demonstrated that, as stand age increased, the storage of SOC and TN increased. These results further indicated that restoration with S. cheilophila has positive impacts on the Gonghe Basin and has increased the capacity of SOC sequestration and N storage. The shrub's role as carbon sink is compatible with system management and persistence. The findings are significant for assessing C and N sequestration accurately in semi-arid degraded high, cold sandy regions in the future.

Description: Failure of high earth dams under earthquake may cause disastrous economic damage and loss of lives. It is necessary to conduct seismic safety assessment, and numerical analysis is an effective way. Solid-fluid interaction has a significant influence on the dynamic responses of geotechnical materials, which should be considered in the seismic analysis of earth dams. The initial stress field needed for dynamic computation is often obtained from postulation, without considering the effects of early construction and reservoir impounding. In this study, coupled static analyses are conducted to simulate the construction and impounding of an ultra-high earth rockfill dam in China. Then based on the initial static stress field, dynamic response of the dam is studied with fully coupled nonlinear method. Results show that excess pore water pressure accumulates gradually with earthquake and the maximum value occurs at the bottom of core. Acceleration amplification reaches the maximum at the crest as a result of whiplash effect. Horizontal and vertical permanent displacements both reach the maximum values at the dam crest.

Description: Land Surface Temperature (LST) is a key variable (commonly studied to understand the hydrological cycle) that helps drive the energy balance and water exchange between the Earth's surface and its atmosphere. One observable constituent of much importance in the land surface water balance model is snow. Snow cover plays a critical role in the regional to global scale hydrological cycle because rain-on-snow with warm air temperatures accelerates rapid snow-melt, which is responsible for the majority of the spring floods. Accurate information on near-surface air temperature (T-air) and snow skin temperature (T-skin) helps us comprehend the energy and water balances in the Earth's hydrological cycle. T-skin is critical in estimating latent and sensible heat fluxes over snow covered areas because incoming and outgoing radiation fluxes from the snow mass and the air temperature above make it different from the average snowpack temperature. This study investigates the correlation between MODerate resolution Imaging Spectroradiometer (MODIS) LST data and observed T-air and T-skin data from NOAA-CREST-Snow Analysis and Field Experiment (CREST-SAFE) for the winters of 2013 and 2014. LST satellite validation is imperative because high-latitude regions are significantly affected by climate warming and there is a need to aid existing meteorological station networks with the spatially continuous measurements provided by satellites. Results indicate that near-surface air temperature correlates better than snow skin temperature with MODIS LST data. Additional findings show that there is a negative trend demonstrating that the air minus snow skin temperature difference is inversely proportional to cloud cover. To a lesser extent, it will be examined whether the surface properties at the site are representative for the LST properties within the instrument field of view.

Description: The Gonghe Basin is a sandified and desertified region of China, but the distribution of soil organic carbon (SOC) and total nitrogen (TN) along the cultivation chronosequence across this ecologically fragile region is not well understood. This study was carried out to understand the effects of afforestation with Salix cheilophila for different periods of time (6, 11, 16, 21 years) to test whether it enhanced C and N storage. Soil samples, in four replications from seven depth increments (every 10 cm from 0 to 30 cm, every 20 cm from 30 to 50 cm and every 50 cm from 50 to 200 cm), were collected in each stand. Soil bulk density, SOC, TN, aboveground biomass and root biomass were measured. Results indicated that changes occurred in both the upper and deeper soil layers with an increase in revegetation time. The 0–200 cm soil showed that the 6-year stand gained 3.89 Mg C ha−1 and 1.00 Mg N ha−1, which accounted for 40.82% of the original SOC and 11.06% of the TN of the 0-year stand. The 11-year stand gained 7.82 Mg C ha−1 and 1.98 Mg N ha−1 in the 0–200 cm soil layers, accounting for 58.06% of the SOC and 19.80% of the TN of the 0-year stand. The 16-year stand gained 11.32 Mg C ha−1 and 3.30 Mg N ha−1 in the 0–200 cm soil layers, accounting for 66.71% of the SOC and 21.98% of the TN of the 0-year stand. The 21-year stand gained 13.05 Mg C ha−1 and 5.45 Mg N ha−1 from the same soil depth, accounting for 69.79% of the SOC and 40.47% of the TN compared with the 0-year stand. The extent of these changes depended on soil depth and plantation age. The results demonstrated that as stand age increased, the storage of SOC and TN increased. These results further indicated that afforestation with S. cheilophila has positive impacts on the Gonghe Basin and has increased the capacity of SOC sequestration and N storage. Shrub's role as carbon sink is compatible with system's management and persistence. The findings are significant for assessing C and N sequestration accurately in semi-arid degraded high-cold sandy regions in the future.