The Future of Scattered Trees in Agricultural Landscapes

Abstract: Mature trees scattered throughout agricultural landscapes are critical habitat for some biota and provide a range of ecosystem services. These trees are declining in intensively managed agricultural landscapes globally. We developed a simulation model to predict the rates at which these trees are declining, identified the key variables that can be manipulated to mitigate this decline, and compared alternative management proposals. We used the initial numbers of trees in the stand, the predicted ages of these trees, their rate of growth, the number of recruits established, the frequency of recruitment, and the rate of tree mortality to simulate the dynamics of scattered trees in agricultural landscapes. We applied this simulation model to case studies from Spain, United States, Australia, and Costa Rica. We predicted that mature trees would be lost from these landscapes in 90–180 years under current management. Existing management recommendations for these landscapes—which focus on increasing recruitment—would not reverse this trend. The loss of scattered mature trees was most sensitive to tree mortality, stand age, number of recruits, and frequency of recruitment. We predicted that perpetuating mature trees in agricultural landscapes at or above existing densities requires a strategy that keeps mortality among established trees below around 0.5% per year, recruits new trees at a rate that is higher than the number of existing trees, and recruits new trees at a frequency in years equivalent to around 15% of the maximum life expectancy of trees. Numbers of mature trees in landscapes represented by the case studies will decline before they increase, even if strategies of this type are implemented immediately. This decline will be greater if a management response is delayed.     

生物质燃烧对东南亚及中国南方对流层臭氧含量影响的模拟研究

利用区域气候和大气化学模式系统,对2000年春季生物质燃烧排放影响东南亚及中国南部地区对流层臭氧含量进行模拟研究.结果表明,春季东南亚和南亚的生物质燃烧不仅影响源区对流层臭氧含量,而且对处于环流下游的中国南部地区也有显著作用;燃烧源区主要影响对流层低层,下游地区则影响对流层中低层.在源区引起的对流层臭氧总浓度增加达2.1×10^-1g/m²,对下游的中国南部地区增加量为9.0～12.0×10^-2g/m²;源区大气低层1000～900hPa的臭氧含量可增加36×10^-9m³/m³ 以上,而在中国南部750～700hPa高度上空的增加达15×10^-9m³/m³.     

The explosion of non-nano iron dust suspension in the 20-l spherical bomb

The understanding of dust explosion is still incomplete because of the lack of reliable data and accurate models accounting for all the physic-chemical aspects. Besides, most of the experimental data available in the current literature has been accumulated on the 20-l spherical bomb tests, which gives coarse results for the pressure history that cannot be easily converted into fundamental combustion parameters. Nevertheless, the large amount of experimental data available in the spherical bomb is attractive. In this work, the explosion of non-nano iron dust in the standard spherical vessel is analyzed, aiming at evaluating the burning velocity from the theoretical point of view and the simple experiments performed by the standard explosion tests. The choice of iron is of relevance because its adiabatic flame temperature is below the boiling temperature of both the reactants and oxidized gaseous, liquid, or solid (intermediate and final) products and for the negligible particle porosity, which instead is typical of organic dust. Therefore, a non-nano iron dust explosion can be reconducted to a reduced mechanism since heterogeneous (surface) combustion may be determinant, and the diffusion mechanism for oxygen is the only relevant. The laminar burning velocity is strongly dependant on the particle diameter, whereas little effects are due to the dust concentration. The reported final value was found in agreement with typical limiting laminar burning velocity, adopted for the estimation of flammability limits.     

Consequence risk analysis using operating procedure event trees and dynamic simulation

Faults due to human errors cost the petrochemical industry billions of dollars every year and can have adverse environmental consequences. Unquantified human error probabilities exist during process state transitions performed each day by process operators using standard operating procedures. Managing the risks associated with operating procedures is an essential part of managing the overall safety risk. Additional operator training and safety education cannot eliminate all such faults due to human errors; therefore, we propose an operating procedure event tree (OPET) like analysis with branches and events specifically designed to perform risk analysis on operating procedures. The OPET method adapts event trees to analyze the risk due to human error while performing operating procedures. We consider human error scenarios during the procedure and determine the likely consequences by applying dynamic simulation. The modified event tree provides an estimate of the error frequencies.Operating procedure steps were developed, and potential operator faults were determined for two typical equipment switching procedures found in chemical plant operations. Then, dynamic simulation using Aspen HYSYS software was applied to determine the overpressure related consequences of each fault. Finally, the error frequencies resulting from those scenarios were analyzed using operating procedure event trees. We found that a typical ethylene plant gas header would overpressure with 0.6% frequency per manual dryer switch. Since dryer switches occur from every few days up to once per shift, these results suggest that dryer switching should be automated to ensure safe and environmentally friendly operation. Process dryer switching performed manually by operators opening and closing gate valves can be automated with control valves and a distributed control system. A sample distillation column was found to overpressure with 0.85% frequency per manual reflux pump switch.     

春节期间燃放烟花爆竹对我国城市空气质量影响分析

对2013年、2014年我国部分城市春节期间空气质量数据进行分析,结果表明:集中燃放烟花爆竹对我国城市环境空气质量造成了严重影响,大部分城市在集中燃放日出现空气质量超标现象;燃放烟花爆竹可以导致空气中PM10、PM2.5等污染物浓度显著上升;燃放活动还可以导致PM2.5中K、Ba、Pb、Cu等元素含量明显上升;集中燃放烟花爆竹对颗粒物小时浓度值、日均值和年均值均有一定的贡献。     

麦秸焚烧导致的北京市大气污染时空分布和化学组成特征分析

为了全面评价农田秸秆焚烧产生的污染事件,并为制定有效的管理措施提供依据,于2006年6月20日监测了西南风下北京南部农田麦秸焚烧产生的污染物向北京传输的过程.获得了SO2、CO、NOx以及可吸入颗粒物(PM10)质量浓度的数据.颗粒物的化学组分数据.数据分析结果表明,污染输送对北京市西南部地区空气质量影响最大(PM10小时浓度超过600μg·m-3),对北部山区影响较小(PM10浓度峰值在110μg·m-3).高浓度污染在市区持续时间最长.麦秸焚烧通过输送增加了PM10(尤其是PM1)、CO、NO2以及NMHC等污染物质,这使得与前一日相比污染物之间的相关关系发生了变化:SO2与其它污染物的相关性不显著,而CO与NO2、CH4与NO显著相关.因子分析进一步揭示,气象条件对污染物浓度变化具有主导作用,而由麦秸焚烧所产生的外来污染源属于次要地位.污染输送过程中,PM25中的硝酸盐类和有机碳、碳黑质量浓度增大.麦秸焚烧所输送的气态污染物和细小颗粒物对人体健康存在威胁,在不利扩散的气象条件下在大气中存留时间加长.研究结果表明,气象条件不利于污染扩散时必须禁止农田秸秆焚烧.     

古水稻土中多环芳烃的分布特征及其来源判定

测定了马家浜文化(距今约6 000a)遗址2个剖面表层土壤、古代水稻土和古代旱地土壤、以及底层土壤中15种多环芳烃的含量,并对其可能来源进行了判定.结果表明,表层土壤中PAHs的含量分别为202.9μg·kg^-1和207.7μg·kg^-1,主要来源于大气沉降;古水稻土中PAHs含量明显降低,仅为56.0μg·kg^-1,但高于古旱地土壤及底层土壤。古旱地土壤及底层土壤PAHs含量在32.0～36.9μg·kg^-1.古水稻土中,2环和3环所占比例较大,达63%,萘和菲含量最高,而4环以上的多环芳烃含量较低.Phe/Ant和BaA/Chr比值和有机质¹³C-NMR图谱显示,古水稻土中的多环芳烃主要来源于水稻秸秆的焚烧,同时还原条件下的生物合成可能是其另一个重要来源.     

燃烧油品的沸溢特性分析研究

分析了油罐火灾中燃烧油品的沸溢现象,阐述了沸溢发生的条件,研究了沸溢时火焰的热辐射强度,研究表明沸溢时火焰温度平均升高300℃左右,火焰平均热辐射强度是沸溢发生前的2.5～3倍.     

长江中下游地区空气质量的数值模拟研究

根据2002年在ACE-Asia和TRACE-P试验中获得的亚洲区域的污染源排放资料,利用美国EPA最新发展的空气质量模式Models-3,分别模拟研究生物源和人为源排放于2002年7月2日08时至7月3日07时在长江中下游地区引起的O3、SO2、CO以及NOx浓度的变化规律和特征.结果显示,模式对污染物具有很好的模拟能力,无论是污染物浓度的日变化还是PBL层内垂直分布情况,都与已有结论和观测结果一致.     

长江三角洲地区秸秆露天焚烧大气污染物排放清单及其在空气质量模式中的应用

基于长江三角洲江苏、安徽、浙江和上海地区2008年粮食产量的统计年鉴,结合作物谷草比、排放因子等估算了上述地区2008年秸秆焚烧排放污染物清单,重点完善了各县级市污染物排放.结果表明2008年江苏、安徽、浙江和上海地区SO2、NOx、CO、CO2、PM2.5、BC、OC、NH3、CH4、NMVOC的排放总量分别为14.28、86.01、1 744.56、36 893.03、517.54、11.74、114.63、19.93、89.37和208.57 kt.江苏中部和北部、安徽北部地区秸秆露天焚烧污染物排放较多,而江苏南部和浙江地区污染物排放量较少.将建立的秸秆露天焚烧排放污染物清单应用于WRF-CMAQ空气质量模式,结果表明,考虑秸秆焚烧排放源后,对PM10、CO等大气污染物的模拟能力大幅提高,模拟浓度比使用原始排放源分别提高42%和28%,模拟浓度与实测浓度的相关系数分别提高0.25和0.17,模拟值较使用原始排放源更加贴近实测值.