Physical and Chemical Properties of Aerosols in the Marine Boundary Layer

9311213海洋边界层中的硫酸盐化合物是大洋二甲基硫化物氧化成硫酸和甲烷磺酸后形成的，这些化合物随后的成核和冷凝是该部分大气中颗粒物的主要来源。这些化合物在相互竞争的成核和冷凝过程之间的分配决定了(与去除过程一起)所产生的气溶胶数量和质量随颗粒大小的分布。这些形成过程与先前存在或产生的气溶胶之间有很强的相互作用。根据大气条件的不同，颗粒形成、生长和去除的特征时间为几分钟到几天。MBL中的颗粒相硫及其与海洋层云的相互作用被假设为对全球气候具有重要作用，无论是通过改变云的辐射性质、寿命或地理范围。这项研究将集中在MBL中的粒子的物理和化学上。项目的总体目标将是确定硫酸盐化合物对气溶胶数量和质量尺寸谱的功能子集或模式的贡献程度，以及这些颗粒和颗粒物的形成过程。超细模式(直径10 nm)代表了最近在MBL中通过气相冷凝形成的那些粒子。聚集模式(直径80~1000 nm)代表了MBL中硫酸盐和光学有效粒子的主要质量。云凝结核(CCN)是由大小化学和水汽过饱和度定义的粒子总数中的一个子集，是云成核的有效粒子。对于海洋层积云，它们的覆盖范围一般大于直径约50纳米。海藻模式包括海藻或经修改的海藻颗粒，这些海藻颗粒在海面上由于风浪作用而破碎薄膜而产生大于100 nm的颗粒。由于它们的碱性化学，这些粒子可能会对MBL中SO2的氧化产生不成比例的大影响，无论是在云内还是云外。Atiken模式在数字的基础上大致覆盖了10到80 nm的范围，它代表了那些几天前就已经存在并且在云过程中没有活动过的粒子。将使用多种物理、光学和化学方法来表征直径在0.003到10微米之间的颗粒的数密度、化学成分、吸湿和热性能的分布。将使用积分浊度计直接测量气溶胶的积分光学性质。直接测量CCN浓度将在热扩散云室中进行。测量方案中有相当大的冗余度，以限制结果的不确定性。将进行实验室测量，以校准和相互比较这些方法。实地研究将在更大的多学科项目范围内进行，这些项目将处理整个硫循环，其中将测量MBL的气相成分。将在华盛顿西北海岸、中太平洋和南半球塔斯马尼亚和格里姆角背景监测站附近的几个地点进行实地试验。

9311213 Covert The formation of sulfate compounds in the marine boundary layer (MBL) from the oxidation of oceanic dimethyl sulfide (DMS) to sulfuric acid (H2SO4) and methane sulfonic acid (MSA) and the subsequent nucleation and condensation of these compounds is a major source of particulate matter in that part of the atmosphere. The partitioning of these compounds between the competing processes of nucleation and condensation determines (along with removal processes) the resultant distribution of aerosol number and mass with particle size. There is strong interaction between these formation processes and the preexisting or resulting aerosol. The characteristic times for particle formation, growth and removal encompass minutes to days depending on atmospheric conditions. Particulate phase sulfur in the MBL and its interaction with marine stratus clouds are hypothesized to have a significant role in global climate either by altering radiative properties, lifetime or geographical extent of the clouds. This research will focus on physics and chemistry of particles in the MBL. The overall project goal will be to determine the extent to which sulfate compounds contribute to functional subsets or modes of the aerosol number and mass size spectrum and the processes by which these particles and particulate mass are formed. The ultrafine mode, (10nm in diameter) is representative of those particles most recently formed in the MBL by condensation from the gas phase. The accumulation mode (80 to 1000nm diameter) is representative of the main mass of sulfate and optically effective particles in the MBL. Cloud condensation nuclei (CCN), those particles effective in cloud nucleation, are a subset of the total particle population defined by size chemistry and water vapor supersaturation. For marine stratocumulus they generally encompass the range greater than ca. 50nm diameter. The seasalt mode consists of seasalt or modified seasalt particles greater than 100nm generated at the surface by breaking films due to wind and wave action. Due to their alkaline chemistry these particles may have a disproportionately large influence on oxidation of SO2 in the MBL, both in and out of cloud. The Atiken mode, which on a number basis loosely covers the range 10 to 80nm, represents those particles that are several days of age and have not been active in cloud processes. Several physical, optical and chemical methods will be used to characterize the distribution of number concentration, chemical composition, hygroscopic and thermal properties of the particles between 0.003 and 10um diameter. Direct measurements of integral optical properties of the aerosol will be made with an integrating nephelometer. Direct measurements of the CCN concentration will be made in a thermal diffusion cloud chamber. There is considerable redundancy in the measurement scheme to constrain the uncertainty of the results. Laboratory measurements will be done to calibrate and intercompare the methods. The field research will be carried out within the context of larger multidisciplinary projects that will address the overall sulfur cycle in which gas phase composition of the MBL will be measured. Field experiments will be done at several locations, along the NW coast of Washington, in the mid-Pacific and in the Southern Hemisphere in the vicinity of Tasmania and the Cape Grim Background Monitoring Station.