Ergonomics and Aerosol Technology, ‡Division of Nuclear Physics, and §Solid State Physics, Lund University , P.O. Box 118, SE-221 00, Lund, Sweden.
Environ Sci Technol. 2014 Jun 3;48(11):6300-8. doi: 10.1021/es5000353. Epub 2014 May 14.
In urban environments, airborne particles are continuously emitted, followed by atmospheric aging. Also, particles emitted elsewhere, transported by winds, contribute to the urban aerosol. We studied the effective density (mass-mobility relationship) and mixing state with respect to the density of particles in central Copenhagen, in wintertime. The results are related to particle origin, morphology, and aging. Using a differential mobility analyzer-aerosol particle mass analyzer (DMA-APM), we determined that particles in the diameter range of 50-400 nm were of two groups: porous soot aggregates and more dense particles. Both groups were present at each size in varying proportions. Two types of temporal variability in the relative number fraction of the two groups were found: soot correlated with intense traffic in a diel pattern and dense particles increased during episodes with long-range transport from polluted continental areas. The effective density of each group was relatively stable over time, especially of the soot aggregates, which had effective densities similar to those observed in laboratory studies of fresh diesel exhaust emissions. When heated to 300 °C, the soot aggregate volatile mass fraction was ∼10%. For the dense particles, the volatile mass fraction varied from ∼80% to nearly 100%.
在城市环境中，空气传播的颗粒物不断被排放出来，随后经历大气老化。此外，其他地方排放的、被风输送而来的颗粒物也会对城市气溶胶做出贡献。我们研究了哥本哈根市中心冬季颗粒物的有效密度（质量-迁移率关系）和混合状态，这与颗粒物的来源、形态和老化有关。我们使用差分迁移率分析仪-气溶胶粒子质量分析仪（DMA-APM）发现，直径在 50-400nm 范围内的颗粒物分为两组：多孔烟尘聚集体和密度更大的颗粒。这两组颗粒在每个尺寸上都以不同的比例存在。我们发现了两种类型的两组颗粒相对数量分数的时间变化：烟尘与昼夜模式下的密集交通相关，而密集颗粒则在来自污染大陆地区的长距离传输期间增加。每组的有效密度随时间相对稳定，尤其是烟尘聚集体，其有效密度与实验室对新鲜柴油排放物的研究中观察到的相似。当加热到 300°C 时，烟尘聚集体的挥发性质量分数约为 10%。对于密集颗粒，挥发性质量分数从约 80%到接近 100%不等。
