3:45 PM - 4:00 PM
[AAS11-25] Variation in the number concentration of ice nucleating particles at Mt. Tsukuba, Japan
Keywords:aerosol, bioaerosol, Ice Nucleating Particle, INP
The change of the amount of ice crystals in a mixed-phase cloud can influence microphysical processes in the clouds, thereby affecting its cloud properties (cloud lifetime, precipitation, and radiation balance). Ice crystal formation in the mixed-phase cloud requires the presence of aerosol particles that act as its nuclei (Ice nucleating particles, INPs). Previous studies have suggested that mineral dust particles and some bioaerosol particles can act as effective INPs [1]. However, due to the limited observational knowledge of INPs in the atmosphere, the quantitative impact of variations in the concentration of these atmospheric aerosol particles on INPs concentration remains uncertain. In particular, basic knowledges of bioaerosol particles in the atmosphere, such as their concentration, species, and spatiotemporal behavior, are still insufficient. Moreover, the ice nucleation activity of bioaerosol particles can vary significantly depending on their spices. Therefore, it is also necessary to clarify the relationship between INPs and bioaerosol particles to improve our understandings of INPs in the atmosphere. So, focusing on the concentration of the atmospheric aerosol particles, especially mineral dust and bioaerosol particles, we measured INPs concentration simultaneously with those aerosol particle observations at Mt.Tsukuba observation site (36.225° N, 140.098° E; 877 m a.s.l.).
For measurement of INPs, the atmospheric aerosol particles were collected on polycarbonate membrane filters (φ47 mm, pore size: 0.4 µm, Cytiva) using vacuumed pump at flow rate of 5 L/min for 167 hours. A piece of the filter sample (φ11 mm) was suspended in ultra pure water (1 mL). About 100 droplets of 2.5 µl were placed on a cooling plate coated with Vaseline and cooled at 1 °C/min while introducing dry air at about 0.7 L/min and the freezing temperature of each droplet was recorded. In addition, to measure the concentration of heat-resistant INPs such as those from mineral dust particles, the suspensions were also measured in the same way after being heated in a water bath at 95°C for 30 minutes[2]. During the same periods of particle collection, the number concentration of the aerosol particles was observed using Optical Particle Counter (OPC, KC-01E, RION), Polarization OPC (POPC, YGK) and Wideband Integrated Bioaerosol Sensor (WIBS, DMT) at the site. Here, we present the results from April to August in 2024.
During this period, the number concentration of INPs which are active by -15°C ranged approximately 0.01 - 1.64 /L, and at -20°C it was approximately 0.16 - 1.00 /L. The Ice Nucleation Active Site (INAS) density at -15°C was approximately 0.39 - 154 /cm2, and at -20°C it was approximately 3.04 - 168 /cm2. We found no clear seasonal trend in INPs concentration and INAS density during this period. However, relatively high values were sometimes observed during the period when Asian dust was transported over the area. Also, a comparison of the INPs concentration measured in this study with those empirically estimated from the number concentration of particles 0.5 µm or larger [3] suggests that the estimated INPs concentration are generally underestimated, except for some periods. Comparing the observed fluorescent bioaerosols particles with the INPs, the number fraction of the biological particles containing riboflavin in the atmospheric particles, which are larger than 0.5 µm, showed a relatively strong correlation with INAS density at -15°C. Meanwhile, since this trend was not clear at lower freezing temperature, these results suggest that the activity of bioaerosols as INPs depended on the temperature at which ice crystal formation in the clouds. To make sure that a similar trend is observed over a longer period, these observations need to be continued.
[1] Creamean, et al., 2013, Science, 339, 1572-1578.
[2] Tobo, 2016, Sci. Rep., 6.
[3] DeMott, et al., 2010, PNAS, 107.25, 11217-11222.
For measurement of INPs, the atmospheric aerosol particles were collected on polycarbonate membrane filters (φ47 mm, pore size: 0.4 µm, Cytiva) using vacuumed pump at flow rate of 5 L/min for 167 hours. A piece of the filter sample (φ11 mm) was suspended in ultra pure water (1 mL). About 100 droplets of 2.5 µl were placed on a cooling plate coated with Vaseline and cooled at 1 °C/min while introducing dry air at about 0.7 L/min and the freezing temperature of each droplet was recorded. In addition, to measure the concentration of heat-resistant INPs such as those from mineral dust particles, the suspensions were also measured in the same way after being heated in a water bath at 95°C for 30 minutes[2]. During the same periods of particle collection, the number concentration of the aerosol particles was observed using Optical Particle Counter (OPC, KC-01E, RION), Polarization OPC (POPC, YGK) and Wideband Integrated Bioaerosol Sensor (WIBS, DMT) at the site. Here, we present the results from April to August in 2024.
During this period, the number concentration of INPs which are active by -15°C ranged approximately 0.01 - 1.64 /L, and at -20°C it was approximately 0.16 - 1.00 /L. The Ice Nucleation Active Site (INAS) density at -15°C was approximately 0.39 - 154 /cm2, and at -20°C it was approximately 3.04 - 168 /cm2. We found no clear seasonal trend in INPs concentration and INAS density during this period. However, relatively high values were sometimes observed during the period when Asian dust was transported over the area. Also, a comparison of the INPs concentration measured in this study with those empirically estimated from the number concentration of particles 0.5 µm or larger [3] suggests that the estimated INPs concentration are generally underestimated, except for some periods. Comparing the observed fluorescent bioaerosols particles with the INPs, the number fraction of the biological particles containing riboflavin in the atmospheric particles, which are larger than 0.5 µm, showed a relatively strong correlation with INAS density at -15°C. Meanwhile, since this trend was not clear at lower freezing temperature, these results suggest that the activity of bioaerosols as INPs depended on the temperature at which ice crystal formation in the clouds. To make sure that a similar trend is observed over a longer period, these observations need to be continued.
[1] Creamean, et al., 2013, Science, 339, 1572-1578.
[2] Tobo, 2016, Sci. Rep., 6.
[3] DeMott, et al., 2010, PNAS, 107.25, 11217-11222.