Physical and Chemical Properties of Aerosols in the Marine Boundary Layer

在海洋边界层（MBL）中，由海洋二甲基硫化物（DMS）氧化生成硫酸（H2SO4）和甲烷磺酸（MSA）以及随后这些化合物的成核和冷凝形成的硫酸盐化合物是该部分大气中颗粒物质的主要来源。这些化合物在相互竞争的成核和冷凝过程之间的分配（连同去除过程）决定了气溶胶数量和质量随粒径的最终分布。这些形成过程与先前存在的或由此产生的气溶胶之间有很强的相互作用。根据大气条件，颗粒形成、生长和去除的特征时间从几分钟到几天不等。假设MBL中的颗粒相硫及其与海洋层云的相互作用通过改变云的辐射特性、寿命或地理范围对全球气候具有重要作用。本研究将重点研究MBL中粒子的物理和化学性质。该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大小谱的功能亚群或模式的贡献程度，以及这些颗粒和颗粒质量形成的过程。超细模式（直径为10nm）代表了最近在MBL中由气相冷凝形成的颗粒。堆积模式（直径80 ~ 1000nm）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）是云成核中有效的粒子，是由大小、化学和水蒸气过饱和度定义的总粒子群的一个子集。对于海洋层积云，它们通常包含直径大于约50纳米的范围。海盐模式是由大于100nm的海盐或改性海盐粒子在风和波浪作用下在表面破膜而产生的。由于它们的碱性化学性质，这些颗粒可能对云内外MBL中SO2的氧化产生不成比例的大影响。Atiken模式，在数字基础上大致覆盖了10到80nm的范围，代表了那些已经存在了几天并且在云过程中没有活跃的颗粒。将使用几种物理、光学和化学方法来表征直径在0.003至10um之间的颗粒的数目浓度、化学组成、吸湿性和热性能的分布。直接测量气溶胶的积分光学特性将用积分浊度计进行。CCN浓度的直接测量将在热扩散云室中进行。在测量方案中有相当多的冗余来约束结果的不确定度。将进行实验室测量以校准和比较这些方法。现场研究将在更大的多学科项目的背景下进行，这些项目将解决MBL气相组成测量的整个硫循环问题。实地实验将在几个地点进行，包括华盛顿西北海岸、太平洋中部以及南半球塔斯马尼亚岛和格里姆角背景监测站附近。

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.