Hygroscopic properties of ultrafine aerosol particles in the boreal forest: diurnal variation, solubility and the influence of sulfuric acid
Hygroscopic properties of ultrafine aerosol particles in the boreal forest: diurnal variation, solubility and the influence of sulfuric acid
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DOI：
10.5194/acp-7-211-2007
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发表时间：
2006-10
影响因子：
6.3
通讯作者：
M. Ehn;T. Petäjä;H. Aufmhoff;P. Aalto;K. Hämeri;F. Arnold;A. Laaksonen;M. Kulmala
中科院分区：
文献类型：
--
作者：
M. Ehn;T. Petäjä;H. Aufmhoff;P. Aalto;K. Hämeri;F. Arnold;A. Laaksonen;M. Kulmala
在相对湿度为88%的条件下，测量了北方森林中气溶胶粒子的吸湿性生长。同时，监测了一种吸湿性很强的化合物--硫酸的气相浓度。焦点主要集中在形核形成新颗粒的天数上。测得的吸湿生长因子(GF)与气相硫酸浓度呈正相关。颗粒越小，相关性越强，50 nm时r=0.20，10 nm时r=0.50。对于初始质量较小的粒子，由于冷凝硫酸而导致的GF增加预计会更大。在新粒子形成过程中，计算了新粒子生长到Aitken模尺寸过程中溶解度的变化。随着模径的增大，颗粒的溶解度降低。这表明，初始颗粒的增长是由于吸湿性较强的化合物造成的，而在晚上和夜间的后期增长主要是由于吸湿性较低甚至疏水性的化合物造成的。对于所有测量的大小，无论有无粒子形成的日子，都观察到了GF的日变化。GF在午夜左右最低，根据颗粒大小和白天是否有新的颗粒形成，其平均值为1.12-1.24，中午左右增加到1.25-1.34。这可以初步用白天和夜间的气相化学来解释；根据一天中的不同时间，会出现不同的蒸气，通过冷凝，这些化合物将以不同的方式改变颗粒的吸湿性。
The hygroscopic growth of aerosol particles present in a boreal forest was measured at a relative humid- ity of 88%. Simultaneously the gas phase concentration of sulfuric acid, a very hygroscopic compound, was monitored. The focus was mainly on days with new particle formation by nucleation. The measured hygroscopic growth factors (GF) correlated positively with the gaseous phase sulfuric acid concentrations. The smaller the particles, the stronger the correlation, with r=0.20 for 50 nm and r=0.50 for 10 nm particles. The increase in GF due to condensing sulfuric acid is expected to be larger for particles with initially smaller masses. During new particle formation, the changes in solu- bility of the new particles were calculated during their growth to Aitken mode sizes. As the modal diameter increased, the solubility of the particles decreased. This indicated that the initial particle growth was due to more hygroscopic com- pounds, whereas the later growth during the evening and night was mainly caused by less hygroscopic or even hy- drophobic compounds. For all the measured sizes, a diur- nal variation in GF was observed both during days with and without particle formation. The GF was lowest at around midnight, with a mean value of 1.12-1.24 depending on par- ticle size and if new particle formation occurred during the day, and increased to 1.25-1.34 around noon. This can be tentatively explained by day- and nighttime gas-phase chem- istry; different vapors will be present depending on the time of day, and through condensation these compounds will alter the hygroscopic properties of the particles in different ways.