ALBERT

Description: The radioactive species radon (222Rn) has long been used as a test tracer for the numerical simulation of large scale transport processes. In this study, radon transport experiments are carried out using an atmospheric GCM with a finite-difference dynamical core, the van Leer type FFSL advection algorithm and two state-of-the-art cumulus convection parameterization schemes. Measurements of surface concentration and vertical distribution of radon collected from literature are used as references in model evaluation. The simulated radon concentrations using both convection schemes turn out to be consistent with earlier studies with many other models. Comparison with measurements indicates that at the locations where significant seasonal variations are observed in reality, the model can reproduce both the monthly mean surface radon concentration and the annual cycle quite well. At those sites where the seasonal variation is not large, the model is able to give a correct magnitude of the annual mean. In East Asia, where radon simulations are rarely reported in literature, detailed analysis shows that our results compare reasonably well with the observations. The most evident changes caused by the use of a different convection scheme are found in the vertical distribution of the tracer. The scheme associated with a weaker upward transport gives higher radon concentration up to about 6 km above the surface, and lower values in higher altitudes. In the lower part of the atmosphere results from this scheme does not agree as well with the measurements as the other scheme. Differences from 6 km to the model top are even larger, although we are not yet able to tell which simulation is better due to the lack of observations at such high altitudes.

Description: The radioactive species radon (222Rn) has long been used as a test tracer for the numerical simulation of large scale transport processes. In this study, radon transport experiments are carried out using an atmospheric GCM with a finite-difference dynamical core, the van Leer type FFSL advection algorithm, and two state-of-the-art cumulus convection parameterization schemes. Measurements of surface concentration and vertical distribution of radon collected from the literature are used as references in model evaluation. The simulated radon concentrations using both convection schemes turn out to be consistent with earlier studies with many other models. Comparison with measurements indicates that at the locations where significant seasonal variations are observed in reality, the model can reproduce both the monthly mean surface radon concentration and the annual cycle quite well. At those sites where the seasonal variation is not large, the model is able to give a correct magnitude of the annual mean. In East Asia, where radon simulations are rarely reported in the literature, detailed analysis shows that our results compare reasonably well with the observations. The most evident changes caused by the use of a different convection scheme are found in the vertical distribution of the tracer. The scheme associated with weaker upward transport gives higher radon concentration up to about 6 km above the surface, and lower values in higher altitudes. In the lower part of the atmosphere results from this scheme does not agree as well with the measurements as the other scheme. Differences from 6 km to the model top are even larger, although we are not yet able to tell which simulation is better due to the lack of observations at such high altitudes.

Description: A total of 834 individual aerosol particles were collected during October and November 2010 in urban Shanghai, China. Particles were sampled under different weather and air quality conditions. Morphologies, compositions and mixing states of carbonaceous aerosols were investigated by transmission electron microscopy (TEM) coupled with energy-dispersive X-ray (EDX). Structures of some particles were verified using selected-area electron diffraction (SAED). Among the aerosol particles observed, carbonaceous aerosols were mainly categorized into four types: polymeric organic compound (POC), soot, tar ball, and biogenic particle. Based on the detailed TEM-EDX analysis, most of the particles were coated with secondary organic aerosols (SOA), which commonly formed through condensation or heterogeneous reactions of precursor gases on pre-existing particles. Aged particles were associated with days with low wind velocities, showed complex structures, and were bigger in size. The internally mixed particles of sulphates, organics and soot were encountered frequently. Such internally mixed particles may be preferentially formed during a stagnated air mass during serious pollution events, such as on 13 November. Although relative number counts varied with different species, sulphates (38–71%) and soot (11–22%) constituted the most dominant species observed in the samples. However, soil-derived particles (68%) were relatively more frequently observed on the sample collected on 12 November during a dust storm.

Description: Tropospheric aerosol size distributions are simulated by three online global models which employ exactly the same aerosol microphysics module, but differ in many aspects such as model meteorology, natural aerosol emission, sulfur chemistry, and deposition processes. The main purpose of this study is to identify the influence of these differences on the aerosol simulation. Number concentrations of different aerosol size ranges are compared among the three models and against observations. Overall all three models are able to capture the basic features of the observed spatial distribution. The magnitude of number concentration is consistent among the three models in all size ranges, although quantitative differences are also clearly detectable. For the soluble and insoluble coarse and accumulation modes, inter-model discrepancies result primarily from the different parameterization schemes for sea salt and dust emission, and are also linked to the different strengths of the convective transport in the meteorological models. As for the nucleation mode and the soluble Aitken mode, the spread of model results appear largest in the tropics and in the middle and upper troposphere. Diagnostics and sensitivity experiments suggest that this large spread is directly related to the sulfur cycle in the models, which is strongly affected by the choice of sulfur chemistry scheme, its coupling with the convective transport and wet deposition calculation, and the related meteorological fields such as cloud cover, cloud water content, and precipitation. Aerosol size distributions simulated by the three models are compared against observations in the boundary layer. The characteristic shape and magnitude of the distribution functions are reasonably reproduced in typical conditions of clean, polluted and transition areas.

Description: A series of emission control measures were undertaken in Beijing and the adjacent provinces in China during the 2008 Beijing Olympic Games on 8–24 August 2008. This provides a unique opportunity for investigating the effectiveness of emission controls on air pollution in Beijing. We conducted a series of numerical experiments over East Asia for the period of July to September 2008 using a coupled meteorology-chemistry model (WRF-Chem). Model can generally reproduce the observed variation of aerosol concentrations. Consistent with observations, modeled concentrations of aerosol species (sulfate, nitrate, ammonium, black carbon, organic carbon, total particulate matter) in Beijing were decreased by 30–50% during the Olympic period compared to the other periods in July and August in 2008 and the same period in 2007. Model results indicate that emission controls were effective in reducing the aerosol concentrations by comparing simulations with and without emission controls. In addition to emission controls, our analysis suggests that meteorological conditions (e.g. wind direction and precipitation) were also important in producing the low aerosol concentrations appearing during the Olympic period. Transport from the regions surrounding Beijing determined the daily variation of aerosol concentrations in Beijing. Based on the budget analysis, we suggest that to improve the air quality over Beijing, emission control strategy should focus on the regional scale instead of the local scale.

Description: Tropospheric aerosol size distributions are simulated by three online global models that employ exactly the same modal approach but differ in many aspects such as model meteorology, natural aerosol emissions, sulfur chemistry, and the parameterization of deposition processes. The main purpose of this study is to identify where the largest inter-model discrepancies occur and what the main reasons are. The number concentrations of different aerosol size ranges are compared among the three models and against observations. Overall all the three models can capture the basic features of the observed aerosol number spatial distributions. The magnitude of the number concentration of each mode is consistent among the three models. Quantitative differences are also clearly detectable. For the soluble and insoluble coarse mode and accumulation mode, inter-model discrepancies mainly result from differences in the sea salt and dust emissions, as well as the different strengths of the convective transport in the meteorological models. For the nucleation mode and the soluble Aitken mode, the spread of the model results is largest in the tropics and in the middle and upper troposphere. Diagnostics and sensitivity experiments suggest that this large spread is closely related to the sulfur cycle in the models, which is strongly affected by the choice of sulfur chemistry scheme, its coupling with the convective transport and wet deposition calculation, and the related meteorological fields such as cloud cover, cloud water content, and precipitation. The aerosol size distributions simulated by the three models are compared to observations in the boundary layer. The characteristic shape and magnitude of the distribution functions are reasonably reproduced in typical conditions (i.e., clean, polluted and transition areas). Biases in the mode parameters over the remote oceans and the China adjacent seas are probably caused by the fixed mode variance in the mathematical formulations used in the modal approach in the three models, as well as some of the prescribed size distribution parameters of the natural and anthropogenic emissions.

Description: The Tropical Niche Conservatism Hypothesis (TCH) tries to explain the generally observed latitudinal gradient of increasing species diversity towards the tropics. To date, few studies have used phylogenetic approaches to assess its validity, even though such methods are especially suited to detect changes in niche structure. We test the TCH using modeled distributions of 1898 woody species in Yunnan Province (southwest China) in combination with a family level phylogeny. Unlike predicted, species richness and phylogenetic diversity did not show a latitudinal gradient, but identified two high diversity zones, one in Northwest and one in South Yunnan. Despite this, the underlying residual phylogenetic diversity showed a clear decline away from the tropics, while the species composition became progressingly more phylogenetically clustered towards the North. These latitudinal changes were strongly associated with more extreme temperature variability and declining precipitation and soil water availability, especially during the dry season. Our results suggests that the climatically more extreme conditions outside the tropics require adaptations for successful colonization, most likely related to the plant hydraulic system, that have been acquired by only a limited number of phylogenetically closely related plant lineages. We emphasize the importance of phylogenetic approaches for testing the TCH.

Description: The influences of nitrification inhibitor (NI) and biochar incorporation on yield-scaled N2O in a vegetable field were studied using the static chamber method and gas chromatography. An experiment was conducted in an intensively managed vegetable field with 7 consecutive vegetable crops in 2012–2014 in southeastern China. With equal annual amounts of N (1217.3 kg N ha−1 yr−1), 6 treatments under 3 biochar amendment rates, namely, 0 t ha−1 (C0), 20 t ha−1 (C1), and 40 t ha−1 (C2), with compound fertilizer (CF) or urea mixed with chlorinated pyridine (CP) as NI, were studied in these field experiments. The results showed that although no significant influence on soil organic carbon (SOC) content or total nitrogen (TN), CP could result in a significant increase in soil pH during the experimental period. CP significantly decreased cumulative N2O emissions by 15.9–32.1% while increasing vegetable yield by 9.8–41.9%. Thus, it also decreased yield-scaled N2O emissions significantly. In addition to the differential responses of the soil pH, biochar amendment significantly increased SOC and TN. Additionally, compared with the treatments without biochar addition, cumulative N2O emissions showed no significant difference in the CF or the CP group treatments but increased slightly (but not significantly) by 7.9–18.3% in the CP group treatments. Vegetable yield was enhanced by 7.1–49.5% compared with the treatments without biochar amendment, and the yield-scaled N2O emissions were thus decreased significantly. Furthermore, treatments applied with CP and biochar incorporation slightly increased yield-scaled N2O emissions by 9.4%, on average, compared with CP-C0. Therefore, the incorporation of CP could serve as an appropriate practice for increasing vegetable yield and mitigating N2O emissions in intensively managed vegetable fields and should be further examined in various agroecosystems.

Description: The Baker Creek watershed (1570 km2), situated in the central interior of British Columbia, Canada, has been severely disturbed by both logging and natural disturbance, particularly by a recent large-scale mountain pine beetle (MPB) infestation (up to 2009, 70.2% of the watershed area had been attacked by MPB) and subsequent salvage logging. The concept of equivalent clear-cut area (ECA) was used to indicate the magnitude of forest disturbance, with consideration of hydrological recovery following various types of disturbance (wildfire, logging and MPB infestation), cumulated over space and time in the watershed. The cumulative ECA peaked at 62.2% in 2009. A combined approach of statistical analysis (i.e. time series analysis) and graphic method (modified double mass curve) was employed to evaluate the impacts of forest disturbance on hydrology. Our results showed that severe forest disturbance significantly increased annual mean flow. The average increment in annual mean flow caused by forest disturbance was 48.4 mm yr−1, while the average decrease in annual mean flow caused by climatic variability during the same disturbance period was 35.5 mm yr−1. The opposite changes in directions and magnitudes clearly suggest an offsetting effect between forest disturbance and climatic variability, with the absolute influential strength of forest disturbance (57.7%) overriding that from climate variability (42.3%). Forest disturbance also produced significant positive effects on low flow and dry season (fall and winter) mean flow. Implications of our findings for future forest and water resources management are discussed in the context of long-term watershed sustainability.

Description: The Baker Creek watershed (1570 km2) situated in the central interior of British Columbia, Canada has been severely disturbed by both human-being logging and natural disturbance, particularly by a recent large-scale mountain pine beetle (MPB) infestation (up to 2009, 70.2% of the watershed area was attacked by MPB) and subsequent salvage logging. The concept of equivalent clear-cut area (ECA) was used to indicate the magnitude of forest disturbance with consideration of hydrological recovery following various types of disturbances (wildfire, logging and MPB infestation) cumulated over space and time in the studied watershed. The cumulative ECA was up to 62.2% in 2009. A combined approach of statistical analysis (time series analysis) with modified double mass curve was employed to evaluate the impacts of forest disturbance on hydrology. Our results showed that severe forest disturbance significantly increased annual mean flow. The average increment in annual mean flow caused by forest disturbance was 48.4 mm yr−1, while the average decrease in annual mean flow caused by climatic variability during the same disturbance period was −35.5 mm yr−1. The opposite change directions and magnitudes clearly suggest offsetting effect between forest disturbance and climatic variability, with the absolute influential strength of forest disturbance (57.7%) overriding that from climate variability (42.3%). Forest disturbances also produced significant positive effect on low flow and dry season (fall and winter) mean flow. Implications of our findings for future forest and water resources management are discussed in the context of long-term watershed sustainability.