报告显示全球土地退化损失等于5%农业GDP（来源：新华社 郭洋）

    联合国4月9日公布的最新数据显示，土地退化带来的损失已相当于全球农业领域国内生产总值 （GDP）的5%，关注土地退化的经济、社会影响，采取可持续的土地管理迫在眉睫。《联合国防治荒漠化公约》第二次科学会议4月9日在德国波恩召开。会议 发布的研究报告显示，全球土地退化导致的直接经济损失差异巨大，非洲地区农业GDP的4%至12%因土地退化而损失，而在危地马拉这一比例竟高达24%。

    土地退化导致的社会成本同样令人不安，全球大约8.7亿人处于长期饥饿状态。在乌兹别克斯坦，土地退化导致粮食减产20%至30%。2011年的干旱导致东非地区接近370万人口需要食品援助。

    1992年，联合国曾就荒漠化、土地退化和干旱导致的经济损失展开评估，当时得出的结论为每年导致直接经济损失420亿美元。不过，《联合国防治荒漠化公约》秘书处执行秘书吕克·尼亚卡贾表示，当年的评估相对单薄，未将荒漠化带来的间接损失等计算在内。

    《联合国防治荒漠化公约》第二次科学会议将于4月12日闭幕。这次会议旨在对荒漠化、可持 续土地管理及干旱、半干旱和亚湿润干旱区的恢复能力进行更为全面的经济评估，以便为政策制定者提供决策参考。尼亚卡贾说，希望会议能进一步增强人们对干旱 及其影响的认识，实现防治土地退化以及土壤修复的目标。

H. J. Chacon-Madrid K. M. Henry and N. M. Donahue. Photo-oxidation of pinonaldehyde at low NO_x: from chemistry to organic aerosol formation. Atmos. Chem. Phys. 13 3227-3236 2013

Abstract

Pinonaldehyde oxidation by OH radicals under low-NO_x conditions produces significant secondary organic aerosol (SOA) mass yields. Under concurrent UV illumination mass yields are lower than high-NO_x yields published earlier by our group. However when OH radicals are produced via dark ozonolysis the SOA mass yields are comparable at high and low NO_x. Because pinonaldehyde is a major first-generation gas-phase product of α-pinene oxidation by either ozone or OH radicals its potential to form SOA serves as a molecular counterpoint to bulk SOA aging experiments involving SOA formed from α-pinene. Both the general tendency for aging reactions to produce more SOA and the sensitivity of the low-NO_x products to UV photolysis observed in the bulk clearly occur for this single species as well. Photochemical oxidation of pinonaldehye and analogous first-generation terpene oxidation products are potentially a significant source of additional SOA in biogenically influenced air masses.

Lihua Xie Shaoyu Lü Mingzhu Liu Chunmei Gao Xinggang Wang and Lan Wu. Recovery of Ammonium onto Wheat Straw To Be Reused as a Slow-Release Fertilizer. J. Agric. Food Chem. 2013 61