An Atmospheric Chemistry Interpretation of Mass Scans Obtained from a Proton Transfer Mass Spectrometer Flown over the Tropical Rainforest of Surinam

Data on a variety of organic gases are presented, obtained with a protontransfer mass spectrometer (PTR-MS) operated during the March 1998 LBA/CLAIREairborne measurement campaign, between 60 and 12500 m over the rainforest inSurinam (2° N–5° N, 54° W–57° W). The instrumentcan detect molecules with a proton affinity greater than water, includingalkenes, dialkenes, carbonyls, alcohols, and nitriles. Many such molecules areemitted from the rainforest (e.g., isoprene) or formed from the oxidation ofprimary emissions (e.g., methylvinylketone (MVK) and methacrolein (MACR)).From a comparison with modelled data; the variation with altitude; previouslyreported biogenic emissions and the time and location of the measurement,possible and probable identities for the significant masses encountered in therange 33–140 amu have been deduced.The main observed protonated masses, postulated identities and observedaverage boundary layer mixing ratios over the rainforest were: 33 methanol(1.1 nmol/mol); 42 acetonitrile (190 pmol/mol); 43 multiple possibilities (5.9nmol/mol), 45 acetaldehyde (1.7 nmol/mol), 47 formic acid (not quantified);59 acetone (2.9 nmol/mol), 61 acetic acid (not quantified), 63 dimethylsulphide (DMS) (289 pmol/mol), 69 isoprene (1.7 nmol/mol), 71 MVK + MACR (1.3nmol/mol), 73 methyl ethyl ketone (1.8 nmol/mol), 75 hydroxyacetone (606pmol/mol), 83 C₅ isoprene hydroxy carbonylsC₅H₈O₂, methyl furan, and cis 3-hexen-1-ol(732 pmol/mol), 87 C₅ carbonyls and methacrylic acid, 95 possibly2-vinyl furan (656 pmol/mol), 97 unknown (305 pmol/mol), 99 cis hexenal (512pmol/mol) and 101 isoprene C₅ hydroperoxides (575 pmol/mol). Somespecies agreed well with those derived from an isoprene only photochemicalmodel (e.g., mass 71 MVK + MACR) while others did not and were observed athigher than previously reported mixing ratios (e.g., mass 59 acetone, mass 63DMS). Monoterpenes were not detected above the detection limit of 300pmol/mol. Several species postulated are potentially important sources ofHO_x in the free troposphere, e.g., methanol, acetone, methyl ethylketone, methyl vinyl ketone and methacrolein.     

气象—化学双向耦合模式（WRF-NAQPMS）研制及其在京津冀秋季重霾模拟中的应用

为解析大气污染物与气象的双向反馈机制及其对气象和环境的影响,建立基于Mie散射理论的气溶胶—光学性质模块,研制气象-化学双向耦合器,以嵌套网格空气质量预报模式NAQPMS(Nested Air Quality Prediction Modeling System)为基础,建立了NAQPMS和中尺度气象模式WRF(Weather Research and Forecasting Model)的双向耦合模式(WRF-NAQPMS)。利用此模式数值模拟了2013年9月27日至10月1日的北京-天津-河北地区一次秋季严重灰霾过程。结果表明,考虑气溶胶辐射反馈的双向耦合模式模拟的气象要素和细颗粒物(PM2.5)浓度与观测结果更为一致。灰霾期间,气溶胶直接辐射效应显著改变了边界层气象要素,北京-天津-河北地区地面接收的太阳短波辐射减少25%,2 m高度的温度平均下降1°C,湍流动能下降20%,10 m高度的风速降低超过0.2 m/s,边界层高度下降25%,使得边界层大气更加静稳,进而造成了重污染地区污染进一步加剧,如石家庄近地面细颗粒物浓度增加可达30%。分析表明灰霾与边界层气象要素之间存在一种正反馈机制,采用该机制的双向耦合模式有利于准确模拟和预报灰霾污染过程。