Rapid evolution of aerosol particles and their optical properties downwind of wildfires in the western US
Rapid evolution of aerosol particles and their optical properties downwind of wildfires in the western US
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DOI：
10.5194/acp-20-13319-2020
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发表时间：
2020-11-11
影响因子：
6.3
通讯作者：
Yokelson, Robert J.
中科院分区：
文献类型：
--
作者：
Kleinman, Lawrence, I;Sedlacek, Arthur J., III;Yokelson, Robert J.
在太平洋西北部进行的生物质燃烧操作项目（BBOP）现场活动的第一阶段，美国能源部G-1飞机被用来跟踪野火烟雾从排放点附近到下风2-3.5小时位置的时间演变。在九次飞行中，我们在不同的顺风距离处对野火羽流进行了重复的横切，从而可以跟踪羽流的时间演变。平均而言，稀释归一化气溶胶质量浓度作为顺风距离的函数变化不大。这种一致性隐藏了一个动态系统，其中主要的气溶胶粒子正在蒸发，而次级粒子正在冷凝。有机气溶胶因此被氧化。在所有样带上，90%以上的气溶胶是有机物。在新排放的烟雾气溶胶中，NH 4+大约相当于NO3。经过2小时的白天老化，NH 4+增加，大约相当于Cl，SO 42和NO3的总和。颗粒尺寸随着顺风距离的增加而增加，导致颗粒更有效地散射。平均超过9次飞行，质量散射效率（MSE）增加了56%，在一次飞行中增加了一倍。从小到大的颗粒质量重新分配的机制进行了讨论。凝结是有效的移动气溶胶从艾特肯积累模式，但产生的MSE只有轻微的增加。由于吸收随年龄的增长几乎保持不变，单次散射的时间演化受年龄相关散射的控制。近火气溶胶具有0.8-0.9的单次散射比（SSA）。老化1至2小时后，SSA通常为0.9或更大。假设全球平均的表面和大气条件下，观测到的年龄依赖SSA将改变野火羽流的直接辐射效应从近零附近的火灾到顺风冷却效应。
During the first phase of the Biomass Burn Operational Project (BBOP) field campaign, conducted in the Pacific Northwest, the DOE G-1 aircraft was used to follow the time evolution of wildfire smoke from near the point of emission to locations 2-3.5 h downwind. In nine flights we made repeated transects of wildfire plumes at varying downwind distances and could thereby follow the plume's time evolution. On average there was little change in dilution-normalized aerosol mass concentration as a function of downwind distance. This consistency hides a dynamic system in which primary aerosol particles are evaporating and secondary ones condensing. Organic aerosol is oxidized as a result. On all transects more than 90 % of aerosol is organic. In freshly emitted smoke aerosol, NH4+ is approximately equivalent to NO3. After 2 h of daytime aging, NH4+ increased and is approximately equivalent to the sum of Cl, SO42, and NO3. Particle size increased with downwind distance, causing particles to be more efficient scatters. Averaged over nine flights, mass scattering efficiency (MSE) increased in similar to 2 h by 56 % and doubled in one flight. Mechanisms for redistributing mass from small to large particles are discussed. Coagulation is effective at moving aerosol from the Aitken to accumulation modes but yields only a minor increase in MSE. As absorption remained nearly constant with age, the time evolution of single scatter albedo was controlled by age-dependent scattering. Near-fire aerosol had a single scatter albedo (SSA) of 0.8-0.9. After 1 to 2 h of aging SSAs were typically 0.9 and greater. Assuming global-average surface and atmospheric conditions, the observed age dependence in SSA would change the direct radiative effect of a wildfire plume from near zero near the fire to a cooling effect downwind.