Assessment of the aerosol water content in urban atmospheric particles by the hygroscopic growth measurements in Sapporo,Japan

Aerosol water content (AWC) of urban atmospheric particles was investigated based on the hygroscopic growth measurements for 100 and 200 nm particles using a hygroscopicity tandem differential mobility analyzer in Sapporo, Japan in July 2006. In most of the humidogram measurements, presence of less and more hygroscopic mode was evident from the different dependence on relative humidity (RH). The volume of liquid water normalized by that of dry particle (V_w(RH)/V_dry) was estimated from the HTDMA data for 100 and 200 nm particles. The RH dependence of V_w(RH)/V_dry was well represented by a fitted curve with a hygroscopicity parameter κ_eff. The κ_eff values for 200 nm particles were in general higher than those for 100 nm particles, indicating a higher hygroscopicity of 200 nm particles. Based on the κ_eff values, the volume mixing ratios of water-soluble inorganic compounds (ammonium sulfate equivalent) were estimated to be on average 31% and 45% for 100 and 200 nm particles, respectively. The diurnal variation of κ_eff, with relatively higher values in the noontime and nighttime and lower values in the morning and evening hours, was observed for both particle sizes. The V_w(RH)/V_dry values under ambient RH conditions were estimated from κ_eff to range from 0.05 to 2.32 and 0.06 to 2.43 for 100 nm and 200 nm particles, respectively. The degree of correlation between κ_eff and V_w(RH)/V_dry at ambient RH suggests a significant contribution of the variation of κ_eff to atmospheric AWC in Sapporo.     

High abundance of gaseous and particulate 4-oxopentanal in the forestal atmosphere

Atmospheric concentrations of 4-oxopentanal (4-OPA) in both gas and particulate phase were measured at the experimental forest, 200 km north of Sapporo, Japan, from August 13 to 15, 2001. 4-OPA was collected using an annular denuder sampling system and measured with a gas chromatography employing benzylhydroxyl oxime derivatization. Its gas phase concentrations ranged from 180 ng m(-3) (44 pptv) to 1570 ng m(-3) (384 pptv), whereas those in the particulate phase were from below the detection limit (25 ng m(-3)) to 207 ng m(-3). The particulate 4-OPA accounted for 28% (particle/(gas+particle)) of the total concentration as the maximum at 06:00 on August 15th (average: 10%). The particulate concentrations of 4-OPA were found to be comparable to those of pinonic acid, indicating that 4-OPA is also an important constituent of organic aerosols in the forestal atmosphere. Here, we report, for the first time, the concentrations of 4-OPA in both gas and particulate phase and its diurnal variations in the forestal atmosphere.     

In situ measurement of isoprene in the marine air and surface seawater from the western North Pacific

Isoprene (2-methyl-1,3-butadiene) was measured on board of R/V Mirai for eight air samples and 14 seawater samples collected in the western North Pacific during ACE-Asia campaign (from 18 to 26 May 2001). The measurements were conducted in situ using a cryo-focus/gas chromatography/mass spectrometry (Cryo/GC/MS). Concentrations of isoprene ranged from 7.2 to 110 parts-per-trillion (pptv) in the marine air, and ranged from below 12 to 94 pmol l⁻¹ in the seawater. Based on these results, sea-to-air fluxes of isoprene were calculated to be 184 and 300 nmol m⁻² day⁻¹ for two samples, and the upper limits of the fluxes were also calculated to be from 32 to 300 nmol m⁻² day⁻¹. Atmospheric isoprene concentrations cannot be explained only by the flux from the seawater. Thus, the concentrations of isoprene in the marine air in western North Pacific should be significantly affected by terrestrial vegetational emission and subsequent long-range atmospheric transport of isoprene.