Chemical compositions and particle number densities of atmospheric aerosols were measured continuously in the coastal area of Seto Inland Sea during the spring of 2015. The mean concentrations of NH4+, NO3-, and water soluble organic nitrogen (ONws) were 1.6, 0.85, and 0.28 μg N m-3, respectively in total sampling mode. NO3- existed in both fine and coarse modes, while NH4+ and ONws existed primarily in fine mode. On the days of normal atmospheric conditions, the amount of ONws contributing to the total nitrogen was about 14% N in both fine and coarse sampling modes. This ratio was equivalent to the amount of NO3- content in fine mode and NH4+ in coarse mode. On the days with polluted atmospheric conditions, the amount of ONws contributing to total nitrogen was about 9.3% N in fine mode and about 5.0% N in coarse mode. This ratio was equivalent to the contributions of NO3- in fine mode and NH4+ in coarse mode. Dry deposition fluxes of particulate NH4+, NO3-, and ONWS in the area were 280, 660, and 83 μg N m-2 day-1, respectively. The flux of NO3- was more effective than any other nitrogen compounds, since the deposition rate depends upon a size distribution. The dry deposition of ONws accounted for about 8.1% of the total nitrogen dry deposition. Thus, ONWS cannot be ignored when considering the nitrogen budget and cycles in this area.
The electrodynamic balance (EDB), where a single charged aerosol can be levitated in space over the periods of hours, provides the opportunity for in situ observation of the suspended droplet. In this technical report, we describe a newly designed EDB system with a high resolution side-view imaging for the observation of a dynamic behavior of mixing state into droplet. A newly developed slim-type EDB consists of two coaxial cylinder electrodes (I.D. 6 mm and O.D. 8 mm) provided independently controlled the DC voltages superimposed on AC high voltage. Furthermore, the ground shield electrode (I.D. 14 mm and O.D. 15 mm) was installed in order to make the distance between levitated droplet and objective lens of optical microscope as close as possible. The shield electrode also played a significant role in preventing the discharge between the objective lens and a pair of cylindrical electrodes. With this instrument, we directly observed the crystallization processes of supersaturated sodium chloride and sodium bromide droplets in space. It is demonstrated that a newly designed EDB system can be a useful tool for understanding the role of internal mixing state of a droplet during the formation of solid particles.
Elemental carbon (EC) is one of the most important aerosol species that damage human health and affect global climate. The Soot Particle Aerosol Mass Spectrometer (SP-AMS) was recently developed for the measurement of refractory black carbon (rBC) via laser induced incandescence and mass spectrometry. In this study, a SP-AMS was used to measure the rBC in both diesel exhaust and aerosols at a traffic intersection. The comparison of rBC with EC concentrations determined by a thermal optical method suggested a necessity of special caution during the data analysis. Namely, (1) rBC must be determined by subtracting the signals at the laser-off from those at the laser-on for the analysis of unit mass resolution data, and (2) because the collection efficiency of the laser evaporator depends on particle morphology, simultaneous measurements of rBC by SP-AMS and EC or BC by other instruments should be carried out to determine the collection efficiency. We also found that the spectrum of carbon cluster ions in the particles emitted from a direct–ignition gasoline vehicle was different from that of diesel exhaust particles. Therefore, the ratio of cluster ions C＋/C3＋ may be a good indicator for distinguishing these two types of particles in the environment.
In this study, the counting efficiencies of optical particle counters (OPC) were evaluated by using AIST-inkjet aerosol generator (AIST-IAG). Among the six particle size channels of an OPC (RION KC-31), the counting efficiencies were evaluated at two size channels (0.5 μm and 5.0 μm) which are used to monitor the cleanliness of the pharmaceutical manufacturing environments. Current industrial standards (ISO 21501-4 or JIS B 9921) define the particle sizes measured by an OPC as PSL-equivalent optical diameters, dPSL, while the particle diameters of IAG-generated particles are defined as volume equivalent diameter, dve. Therefore, we developed a method to experimentally find a dve-value whose dPSL-value measured by an OPC would fall within a desirable range. Particle generation rate of the AIST-IAG was fixed at 50 particles/s, and three types of water-soluble particles with different morphologies were generated: inorganic salt particles (NaCl) which were non-spherical, solid organic particles (lactose) which were near spherical, and a non-volatile liquid particle (ionic liquid). The measured counting efficiencies ranged from 1.000 to 1.005 and their expanded uncertainties ranged from 0.0052 to 0.0053. From these results it was concluded that AIST-IAG is an effective calibration device for precisely evaluating the counting efficiencies of OPC.
Microchip-based high field asymmetric waveform ion mobility spectrometry (FAIMS) was used for the separation of the cluster ions generated by a corona ionizer in laboratory air. The hydrated cluster ions such as NO3-(H2O)n, NO3-HNO3(H2O)n, and HCO3-HNO3(H2O)n dominated the negative ion mass spectrum, while NH4＋(H2O)n along with H3O＋(H2O)n comprised the majority of the ion peaks in the positive ion mass spectrum. FAIMS spectra of these ions were measured using a FAIMS microchip coupled with an atmospheric pressure ionization mass spectrometer. FAIMS spectra of negative ions demonstrated that most of the negative ions tend to increase their mobilities with increasing the electric field strength and that the ions can be separated into up to six groups depending on the differences in ion mobility under a high and a low electric field. Separation of positive ions occurred at lower electric fields than that of negative ions. A single ion peak at low electric fields split into two peaks with increasing the field strength, but they merged to form a single peak again at a higher electric field. Another ion separation was observed to take place at even higher electric fields. This variation of positive ions in FAIMS spectra suggested that the mobilities of the separated ions initially decreased and subsequently increased with increasing the electric field.
In order to obtain a seasonal variation of Asian dust (Kosa) transport frequency over Japan, the number–size distribution of atmospheric aerosol particles was measured using an optical particle counter (OPC) at Mt. Tateyama during 2004–2014. The OPC data were used to calculate the volume concentration of coarse particles (> 1 μm). Data of light detection and ranging (LIDAR) systems at Toyama near the mountain site were also used to assist dust event detection at Mt. Tateyama during the daytime. The dust event days per month at Mt. Tateyama were frequently detected in spring but not found in September, showing a similar seasonality of Kosa events based on the visibility reduction at meteorological observatories. In July and August, a few dust events were detected at Mt. Tateyama. Analysis of average winds and backward air trajectories suggested that the dust events would be observed at Mt. Tateyama even in summer because of frequent influence of westerly winds during summer.
We studied the formation of non-aggregated Li4Ti5O12 particles by reaction between lithium nitrate and titanium tetraisopropoxide in a methane/oxygen coflow diffusion-flame reactor. We obtained the powder consisting of phase-pure Li4Ti5O12 particles after calcination at 1,073 K. The particles produced in the flame reaction from the spray solution contained an excess amount of lithium corresponding to 25% of the stoichiometric amount. A change in the proportion of virtually non-aggregated particles in TEM images was observed using a rapid cooling of the entire flame aerosol by blowing with cold quenching gas of Ar followed by supercooling in a Laval nozzle placed above the flame. The proportion of non-aggregates was 28% for the particles produced without any cooling steps. When the flame aerosol was supercooled in the Laval nozzle after blowing with 203 K Ar quenching gas, the proportion of non-aggregates was as large as 88%. Thus, rapid cooling in the region of the flame tip is quite effective for preventing particle aggregation.