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Expanding the use of a recently introduced low-cost particle monitor (DC1700 Dylos Air Quality Monitor) for sensing atmospheric PM2.5 requires comparison with data obtained using a certified method for PM2.5 based on appropriate atmospheric observations. Full-year measurements of atmospheric aerosols were taken in Nagoya, Japan during March 2017-March 2018 using the DC1700 to measure the particle number concentrations of >0.5 and >2.5 μm diameter particles and to measure the PM2.5 mass concentration (Mdry, PM2.5) using an automated β attenuation mass monitor (PM712). The number-size distribution was measured using an optical particle counter (KC01D). The dried mass concentration of 0.5-2.5 μm particles (Mdry, 0.5-2.5) was estimated from the ambient relative humidity and the DC1700 number concentration. The values of Mdry, 0.5-2.5 were invariably less than those of Mdry, PM2.5. The coefficient of determination and slope of Mdry, 0.5-2.5 to Mdry, PM2.5 for the year were, respectively, 0.68 and 0.40. Slope values changed seasonally from 0.24 in July and August 2017 to 0.55 in May and April 2017. Light absorbing particles, smaller-fine particles, and the estimation method of Mdry, 0.5-2.5 were inferred as causes of the difference between Mdry, 0.5-2.5 and Mdry, PM2.5. Especially, we estimated a large contribution (ca. 54% underestimation of Mdry, 0.5-2.5 into Mdry, PM2.5) of particles smaller than the minimum detection diameter of DC1700. The seasonal variation of Mdry, 0.5-2.5/Mdry, PM2.5 was related to the volume fraction of particles smaller than 0.5 μm. Good correlation of Mdry, 0.5-2.5 to Mdry, PM2.5 suggests that data obtained using DC1700 with a correction factor are useful as a rough proxy of atmospheric PM2.5 within a season. However, precise estimation of PM2.5 from the DC1700 number concentrations should include appropriate corrections of the size distribution, not only hygroscopicity.

Spheroidal carbonaceous particles (SCPs) are a type of carbonaceous fly ash resulting from high-temperature industrial fossil fuel combustion. In this study, we examined the fluxes, elemental compositions (18 elements including silicon, sulfur, and aluminum but not carbon) and sizes of dry-deposited SCPs in the atmosphere at Cape Hedo (the northernmost part of Okinawa Island) to assess the temporal variation. The study site at Cape Hedo is suitable for investigating atmospherically deposited SCPs, particularly for evaluating their long-range transportation, because Cape Hedo is situated in an outflow region of East Asian pollutants. High SCP fluxes mostly occurred in autumn and winter when air masses came from the Asian continent. Additionally, we determined the temporal variations in the elemental compositions and the sizes of the SCPs during four week-long sampling periods and these results suggest that the high SCP fluxes were due to the transportation of the particles from the Asian continent to the study site. The potential source regions of the particles during respective periods are very consistent with the backward air mass trajectories. Results of our study would imply that sources of the SCPs deposited in the area changed temporarily, and that coarse particulate-pollutants such as SCPs were transported from the eastern Asian continent to Okinawa Island during the periods under specific meteorological conditions. Our findings suggest that the examination of SCPs from atmospheric deposition can contribute to the assessment of atmospheric transportation, specifically for particulate pollutants in the atmospheric boundary layer.

Atmospheric sea-salt and halogen cycles play important roles in atmospheric science and chemistry including cloud processes and oxidation capacity in the Antarctic troposphere. This paper presents a review and summarizes current knowledge related to sea-salt and halogen chemistry in the Antarctic. First, presented are the seasonal variations and size distribution of sea-salt aerosols (SSAs). Second, SSA origins and sea-salt fractionation on sea-ice and ice sheets on the Antarctic continent are presented and discussed. Third, we discuss SSA release from the cryosphere. Fourth, we present SSA dispersion in the Antarctic troposphere and transport into inland areas. Fifth, heterogeneous reactions on SSAs as a source of reactive halogen species and their relationship with atmospheric chemistry are shown and discussed. Finally, we attempt to propose an outlook for obtaining better knowledge related to sea-salt and halogen chemistry and their effects on the Antarctic and the Arctic.

We have measured black carbon (BC) concentrations at Syowa Station, Antarctica, since February 2005. The measured BC concentrations in 2005–2016 were corrected to equivalent BC (EBC) concentrations using Weingartner's method. Seasonal features of EBC concentrations, long-range transport from mid-latitudes to the Antarctic coast, and their origins were characterized. Results show that daily median EBC concentrations were below the detection limit (0.2 ng m−3) to 63.8 ng m−3 at Syowa Station (median, 1.8 ng m−3; mean, 2.7 ng m−3 during the measurement period of February 2005–December 2016). Although seasonal features and year-to-year variations in EBC concentrations were observed, no long-term trend of EBC concentrations was clear during our measurement period. Seasonal features of EBC concentrations showed a spring maximum during September–October at Syowa Station. To elucidate EBC transport processes, origins, and the potential source area (PSA), we compared EBC data to backward trajectory analysis and chemical transport model simulation. From comparison with backward trajectory, high EBC concentrations were found in air masses from the marine boundary layer. This finding implies that transport via the marine boundary layer was the most important transport pathway to EBC concentrations at Antarctic coasts. Some EBC was supplied to the Antarctic region by transport via the upper free troposphere. Chemical transport model simulation demonstrated that the most important origins and PSA of EBC at Syowa Station were biomass burning in South America and southern Africa. Fossil fuel combustion in South America and southern Africa also have important contributions. The absorption Ångström exponent (AAE) showed clear seasonal features with 0.5–1.0 during April–October and maximum (1.0–1.5) in December–February. The AAE features might be associated with organic aerosols and mixing states of EBC.

Concentrations of PM2.5 in Tokyo, a densely populated megacity, often increase because of NH4NO3 formation under low-wind conditions during winter. To obtain source information of NH3 as a NH4NO3 precursor, hourly NH3 and NH4^+ concentrations were measured at an urban site in Tokyo in December 2017. Results show that PM2.5 and NH4^+ concentrations increased simultaneously under low-wind and low-temperature conditions along with NH3, NOx, CO, and optical black carbon (OBC) concentrations. The remaining NH4^+ (herein, ΔNH4^+) subtracted from observed NH4^+ to equivalent SO4^2− concentration correlated well with NO3^− in PM2.5, indicating the existence of fine NH4NO3 particles. Regression analysis of hourly NH3 + ΔΝH4^+ concentrations with CO, NOx, and OBC showed significant correlation. Virtual emission rates (VER) of NH3 per motor vehicle in Tokyo were estimated using observed relations between NH3 + ΔΝH4^+ and OBC, etc. with data from vehicular statistics: they were 3.7–32 mg/km. The regression of NH3 + ΔΝH4^+ with OBC concentrations indicated an intercept of about 3.2 ppb, which is about half of the monthly average in December. This result implies that the non-vehicular source strength was nearly the same strength as the bulk vehicular emissions of NH3 during winter in Tokyo., ファイル公開：2021-06-01

We took aerosol measurements at Syowa Station, Antarctica, to characterize the aerosol number–size distribution and other aerosol physicochemical properties in 2004–2006. Four modal structures (i.e., mono-, bi-, tri-, and quad-modal) were identified in aerosol size distributions during measurements. Particularly, tri-modal and quad-modal structures were associated closely with new particle formation (NPF). To elucidate where NPF proceeds in the Antarctic, we compared the aerosol size distributions and modal structures to air mass origins computed using backward trajectory analysis. Results of this comparison imply that aerosol size distributions involved with fresh NPF (quad-modal distributions) were observed in coastal and continental free troposphere (FT; 12 % of days) areas and marine and coastal boundary layers (1 %) during September–October and March and in coastal and continental FT (3 %) areas and marine and coastal boundary layers (8 %) during December–February. Photochemical gaseous products, coupled with ultraviolet (UV) radiation, play an important role in NPF, even in the Antarctic troposphere. With the existence of the ozone hole in the Antarctic stratosphere, more UV radiation can enhance atmospheric chemistry, even near the surface in the Antarctic. However, linkage among tropospheric aerosols in the Antarctic, ozone hole, and UV enhancement is unknown. Results demonstrated that NPF started in the Antarctic FT already at the end of August–early September by UV enhancement resulting from the ozone hole. Then, aerosol particles supplied from NPF during periods when the ozone hole appeared to grow gradually by vapor condensation, suggesting modification of aerosol properties such as number concentrations and size distributions in the Antarctic troposphere during summer. Here, we assess the hypothesis that UV enhancement in the upper troposphere by the Antarctic ozone hole modifies the aerosol population, aerosol size distribution, cloud condensation nuclei capabilities, and cloud properties in Antarctic regions during summer.

Local meteorological conditions and natural and anthropogenic sources affect atmospheric NH3 concentrations in urban areas. To investigate potential sources and processes of NH3 variation in urban areas, hourly NH3 and NH4+ concentrations were measured during November 2017–October 2019 in Nagoya, a central Japanese megacity. Average NH3 concentrations are high in summer and low in winter. Daily minimum NH3 concentrations are linearly correlated with daily minimum air temperatures. By contrast, daily maximum NH3 concentrations increase exponentially with temperature, suggesting that different nighttime and daytime processes and air temperatures affect concentrations. Short-term increases in NH3 concentrations of two types were examined closely. Infrequent but large increases (11 parts per billion (ppb) for 2 h) occurred after mist evaporation during daytime. During 2 years of observations, only one event of this magnitude was identified in Nagoya, although evaporation of mist and fog occurs frequently after rains. Also, short-term increases occur with a large morning peak in summer. Amplitudes of diurnal variation in NH3 concentration (daily maximum minus minimum) were analyzed on days with nonwet and low wind conditions. Amplitudes were small (ca. 2 ppb) in winter, but they increased from early summer along with new leaf growth. Amplitudes peaked in summer (ca. 20 ppb) because of droppings from hundreds of crows before roosting in trees on the campus. High daily maximum NH3 concentrations were characterized by a rapid increase occurring 2–4 h after local sunrise. In summer, peak NH3 concentrations at around 08:00 local time (LT) in sunny weather were greater than in cloudy weather, suggesting that direct sunlight particularly boosts the morning peak. Daily and seasonal findings related to the morning peak imply that stomatal emission at the site causes the increase. Differences between daily amplitudes during the two summers was explained by the different input amounts of reactive nitrogen from bird droppings and rain, suggesting that bird droppings, a temporary rich source of NH3, affected the small forest canopy.

application/pdf, Article, Atmospheric Environment. 196, p.20-26

Short-term variations of NH3 concentrations in the urban atmosphere are affected by local meteorological conditions and variations of natural and anthropogenic sources. To investigate potential sources and processes of NH3 variation in an urban area, hourly NH3 and NH4+ concentrations were measured from November 2017 through October 2019 in Nagoya, a megacity located in central Japan. Monthly averages of NH3 concentrations were high in summer and low in winter. Daily minimum NH3 concentrations were almost linearly correlated with daily minimum air temperature. In contrast, daily maximum NH3 concentrations revealed an exponential increase with temperature, suggesting that different processes with air temperature acted during the nighttime and daytime. Short-term increases of NH3 concentrations of two types were examined closely. The first is a rare but large increase (11 ppb for 2 hr) after mist evaporation during daytime. It is noteworthy that an event of this magnitude was identified only once during two years of observations at Nagoya even though evaporation of mist or fog droplets is expected to be frequent after rain. The second short-term increase was a large morning peak in summer. After selected days were fulfilled with non-wet and weak wind conditions, the amplitude of diurnal variation of NH3 concentration (daily maximum minus minimum) was analyzed: the amplitude was small (ca. 2 ppb) in winter but it increased from early summer along with new leaf growth. It peaked in summer (up to ca. 20 ppb) during intense addition of droppings from hundreds of crows on trees in the campus assembled before roosting. The high daily maximum NH3 concentration was characterized by a rapid increase occurring 2–4 hr after local sunrise. Daily and seasonal findings related to the morning peak implied that stomatal emission at the site was responsible for the increase. The yearly difference between daily amplitudes during the two summers was explained by the difference in the input amounts of reactive nitrogen derived from bird droppings and some rain, suggesting that the canopy of a small forest affected by the bird droppings might act as a temporary but strong source of NH3.

Mixing states of soot-containing aerosol particles constitute important information for the simulation of climatic effects of black carbon in the atmosphere. To elucidate the mixing states and morphological features of soot-containing particles over remote oceans, we conducted on-board observations over the southern Indian Ocean and the Southern Ocean during the TR/V Umitaka-maru UM-08-09 cruise, which started from Benoa, Indonesia, on 1 December 2008 via Cape Town, South Africa, and which terminated in Fremantle, Australia, on 6 February 2009. The light absorption coefficients of size-segregated particles ( 42− and CH3SO3−, suggesting that aged soot-containing particles were transformed by soluble materials derived from dimethyl sulfide (DMS) oxidation. The obtained information of soot at various remote ocean areas is expected to be useful to understand long-range transport processes and to improve simulations of global soot concentration.

Passive samplers based on molecular diffusion are used to measure many organic and inorganic gaseous species in the atmosphere. In this study, the permeation resistance of two types of polytetrafluoroethylene membrane filters (TA300 and PF100, the same manufacturer but different membrane thicknesses) was evaluated and 0.2% NaCl-impregnated and polyamide filters (Nylasorb and Magna, different manufacturers) were compared as adsorbents for nitric acid (HNO3). As a reference, an annular denuder coated with NaCl was used for measuring HNO3 concentration. Based on the observed data and effective sampling area of the passive sampler, the sampling velocity (SV) was estimated and compared with reported values from other studies. The NaCl-impregnated filter had a slightly higher SV than the nylon (polyamide) filters. The SV for the thinner permeation filter, with a larger porosity (TA300) was much higher than the less porous filter (PF100). According to these results, the SV for a HNO3 passive sampler can be adjusted by selecting appropriate permeation filters according to the potential concentration at the sampling site and the maintenance schedule of the sampler.

The Tenth Symposium on Polar Science/Ordinary sessions: [OM] Polar Meteorology and Glaciology, Thu. 5 Dec. / 2F Auditorium , National Institute of Polar Research

Acidity is a critical characteristic of aerosol particles that impacts many atmospheric chemical reactions. However, the measurement of aerosol acidity remains challenging because of the high ionic strength of atmospheric aerosol particles. In this study, we developed and evaluated a direct method for measuring the pH of atmospheric aerosol samples using pH testing paper. We first examined the color responses of six pH testing papers under various ionic strengths and selected the best performing paper for further testing at higher ionic strength. This paper was then tested under realistic high-ionic-strength conditions created using hygroscopic equilibrium under high and constant relative humidity (RH). A KNO3 saturated solution was used to maintain an RH of 92% in an airtight box. Under these conditions, the hygroscopic constituents in aerosol particles form droplets of aqueous solutions that possess high ionic strength. On the basis of these results, a method for the direct pH measurement of aerosol particle samples was developed. The pH of the atmospheric aerosol samples was measured using this method under high RH to demonstrate its versatility. Our results indicate that this method requires more than approximately 12 μg per spot of fine (PM0.2–2.0 in this study) particles to form a detectable droplet. Compared with previous methods, our direct pH measurement method is simpler, more convenient, and reliable for wide application without excess dilution in practice, and it may be used to obtain important basic information required to study atmospheric aerosols.

High PM2. 5 concentrations of around 100 µg m−3 were observed twice during an intensive observation campaign in January 2015 at Fukuoka (33.52° N, 130.47° E) in western Japan. These events were analyzed comprehensively with a regional chemical transport model and synergetic ground-based observations with state-of-the-art measurement systems, which can capture the behavior of secondary inorganic aerosols (SO42−, NO3−, and NH4+). The first episode of high PM2. 5 concentration was dominated by NO3− (type N) and the second episode by SO42− (type S). The concentration of NH4+ (the counterion for SO42− and NO3−) was high for both types. A sensitivity simulation in the chemical transport model showed that the dominant contribution was from transboundary air pollution for both types. To investigate the differences between these types further, the chemical transport model results were examined, and a backward trajectory analysis was used to provide additional information. During both types of episodes, high concentrations of NO3− were found above China, and an air mass that originated from northeast China reached Fukuoka. The travel time from the coastline of China to Fukuoka differed between types: it was 18 h for type N and 24 h for type S. The conversion ratio of SO2 to SO42− (Fs) was less than 0.1 for type N, but reached 0.3 for type S as the air mass approached Fukuoka. The higher Fs for type S was related to the higher relative humidity and the concentration of HO2, which produces H2O2, the most effective oxidant for the aqueous-phase production of SO42−. Analyzing the gas ratio as an indicator of the sensitivity of NO3− to changes in SO42− and NH4+ showed that the air mass over China was NH3-rich for type N, but almost NH3-neutral for type S. Thus, although the high concentration of NO3− above China gradually decreased during transport from China to Fukuoka, higher NO3− concentrations were maintained during transport owing to the lower SO42− for type N. In contrast, for type S, the production of SO42− led to the decomposition of NH4NO3, and more SO42− was transported. Notably, the type N transport pattern was limited to western Japan, especially the island of Kyushu. Transboundary air pollution dominated by SO42− (type S) has been recognized as a major pattern of pollution over East Asia. However, our study confirms the importance of transboundary air pollution dominated by NO3−, which will help refine our understanding of transboundary heavy PM2. 5 pollution in winter over East Asia.

Mixing state of aerosols and optical properties including lidar ratio, particle depolarization ratio, and Angstrom exponent were investigated at Fukuoka in western Japan using a multi-wavelength Mie–Raman lidar (MMRL), various aerosol mass-concentration measurements, and a polarization optical particle counter during Winter–Spring 2015. Aerosol extinction coefficient, backscatter coefficient, and depolarization at 355 and 532 nm and attenuated backscatter coefficient at 1064 nm are obtained from the MMRL measurements. Ten aerosol episodes were classified into three categories (air pollution, mineral dust, and marine aerosol) based on aerosol mass-concentration measurements in the fine-mode (particle diameter Dp

Long-term synergetic fine and coarse mode aerosol observations were analyzed at 1-h intervals at Fukuoka, Japan, from January to June 2015. The GEOS-Chem chemical transport model, including dust and sea-salt acid uptake processes, was used for detailed analysis of observation data. Several Asian dust events and long-range anthropogenic aerosol transport events were observed during our analysis period, and the numerical model generally explained the observed time variation for both fine and coarse mode aerosols. We found that (i) the majority of fine mode NO3– can be considered as long-range transport (LRT) outside of Japan during the cold season, and (ii) the peak timing of fine mode NO3– coincided with that of SO4–, indicating that both aerosols are controlled by LRT. Also, an observed mass concentration ratio of NO3–/SO42– > 0.9 occurred during the cold season, indicating the importance of NO3– as a major contributor to the PM2.5 mass fraction. Finally, we clearly showed that large-scale dust-nitrate outflow from China to Fukuoka was confirmed in all cases of dust events, indicating that the anthropogenic NOx is converted to dust-nitrate and transported to Japan with dust. These results demonstrate the importance of anthropogenic NO3– LRT during the cold season and dust-nitrate LRT for all dust events (even in June).

Two regional chemical transport models were applied to simulate high concentrations of particulate matters (PM) observed in East Asia in January 2015; the first model is the Nested Air Quality Prediction Modeling System (NAQPMS) and the second is the Community Multi-scale Air Quality Model (CMAQ). The variation of PM2.5 in both models showed well agreement with measurements over both eastern China and western Japan. Based on the model results and the aerosol compositions observed in Fukuoka in western Japan, three types of PM long-range transport (LRT) were identified: N-, S-, and D-type. The N episode showed higher fine-mode nitrate (fNO3–) concentrations than fine-mode sulfate (fSO42–), indicating the importance of NO3– LRT. The S episode showed the highest fSO42– concentrations (28.9 µg m–3), which were 3.4-fold higher than fNO3–, due to high relative humidity. During the D episode, dust stagnated in Fukuoka for three days, due to the influence of low- and high-pressure systems; thus, dust LRT is also important in winter besides spring. Both models reasonable explained variations in aerosol components during both N and S episodes; however, both underestimated fSO42– especially during D episode, suggesting that they may miss certain emissions or chemical mechanisms. High coarse-mode NO3– (cNO3–) concentrations (maximum: 6.3 µg m–3), and high cNO3–/fNO3– ratios (maximum: 1.2) were observed during D episode. NAQPMS successfully captured this cNO3– peak after including heterogeneous reactions on dust. Our results emphasize the importance of such heterogeneous processes for understanding the LRT of dust and anthropogenic pollutants over East Asia.

Ground-based observation of the polarization properties of aerosol particles using a polarization optical particle counter (POPC) was made from 27 October 2013, to 31 December 2015, at a suburban site in the Kyushu area of Japan. We found that the depolarization ratio (DR, the fraction of s-polarized signal in the total backward light scattering signal) of aerosol particles showed prominent seasonal variability, with peaks in spring (0.21–0.23) and winter (0.19–0.23), and a minimum value (0.09–0.14) in summer. The aerosol compositions in both fine mode (aerodynamic diameter of particle, Dp Dp Dp > 1 µm) particles. Occurrence of substandard air quality days in Kyushu was closely related with mixed type (coexistence of anthropogenic pollutants and dust particles in the atmosphere), especially in winter and spring, indicating that dust events in the Asian continent played a key role in the cross-boundary transport of continental pollution. Backward trajectory analysis demonstrated that air masses originating from the western Pacific contained large amounts of spherical particles due to the influence of sea salt, especially in summer; however, for air masses from the Asian continent, the dependence of number fraction of spherical particles on air relative humidity was insignificant, indicating the predominance of less-hygroscopic substances (e.g., mineral dust), although the mass concentrations of anthropogenic pollutants were elevated.

We measured equivalent black carbon (EBC) concentrations at Syowa Station, Antarctica from February 2005 to characterize seasonal features of EBC concentrations and their origins, and to monitor long-range transport of aerosols from mid-latitudes to the Antarctic coast. Results show that EBC concentrations were below the detection limit (0.2 ng m−3) to 63.8 ng m−3 at Syowa Station (median, 1.8 ng m−3; mean, 2.7 ng m−3 during the measurement period). Although seasonal features and year-to-year variations of EBC concentrations were observed, no long-term trend of EBC concentrations was clear during our measurement period. Seasonal features of EBC concentrations showed a spring maximum during September–October at Syowa Station. The absorption Ångström exponent (AAE) was 0.5–1.0 during April–October; it reached its maximum values (1.0–1.5) during summer. The AAE features imply that EBC was mixed internally in the Antarctic troposphere and that organic aerosols engendered high AAE in the summer. To elucidate EBC transport processes, origins, and the potential source area (PSA), we compared EBC data to backward trajectory analysis and model simulation. Results show that EBC might be transported directly to Syowa Station from mid-latitudes mainly via the boundary layer and the lower free troposphere. Some BC was transported to Antarctic regions via the upper free troposphere. Biomass burning in South America and southern Africa is the most dominant PSA for BC transported to Syowa Station. Fossil fuel combustion in South America and southern Africa also have important contributions.