Keiichiro Hara

Arctic Study of Tropospheric Aerosol and Radiation (ASTAR) 2000: Arctic haze case study

The ASTAR 2000 (Arctic Study of Tropospheric Aerosol and Radiation) campaign ran from 12 March until 25 April 2000 with extensive flight operations in the vicinity of Svalbard (Norway) from Longyearbyen airport (78.25°N, 15.49°E). It was a joint Japanese (NIPR Tokyo)–German (AWI Bremerhaven/Potsdam) airborne measurement campaign using AWI aircraft POLAR 4 (Dornier 228-101). Simultaneous ground-based measurements were done at the international research site Ny-Ålesund (78.95°N, 11.93°E) in Svalbard, at the German Koldewey station, at the Japanese Rabben station and at the Scandinavian station at Zeppelin Mountain (475 m above sea level). During the campaign 19 profiles of various aerosol properties were measured. In general, the Arctic spring aerosol in the vicinity of Svalbard had significant temporal and vertical variability. A strong haze event occurred between 21 and 25 March in which the optical depth from ground-based observation was 0.18, which was significantly greater than the background value of 0.06. Airborne measurements on 23 March during this haze event showed a high aerosol layer with an extinction coefficient of 0.03 km−1 or more up to 3 km and a scattering coefficient from 0.02 in the same altitude range. From the chemical analyses of airborne measurements, sulfate, soot and sea salt particles were dominant, and there was a high mixing ratio of external soot particles in some layers during the haze event, whereas internal mixing of soot in sulfate was noticeable in some layers for the background condition. We argue that the high aerosol loading is due to direct transport from anthropogenic source regions. In this paper we focus on the course of the haze event in detail through analyses of the airborne and ground-based results.

Variations of constituents of individual sea-salt particles at Syowa station, Antarctica

Sampling of atmospheric aerosol particles was carried out at Syowa station, Antarctica (39.58°E, 69.00°S) in 1998. For a better understanding of sea-salt chemistry in the coastal Antarctic regions, individual sea-salt particles were analysed using a scanning electron microscope equipped with energy dispersive X-ray spectrometer (SEM-EDX). Individual particle analysis indicates that more sea-salt particles were modified in fine particles (0.2–2 µm in diameter) through heterogeneous reactions mainly with gaseous sulfur species in the summer and reactive nitrogen oxides in the winter—spring. In particular, sea-salt particles in the coastal Antarctic atmosphere may be modified by heterogeneous reactions with not only SO2 and H2SO4 but also volatile sulfur species (e.g. CH3SO3H, DMS and DMSO) derived from bioactivity on the ocean surface during the summer. Also, low air temperature and a larger extent of sea ice offshore Syowa probably enhanced release of fractionated sea-salt particles (S-rich, Mg-rich, K-rich and Ca-rich) from the surface of snow and sea ice, particularly in September—October 1998. In addition, we attempt to estimate the scavenging rate of atmospheric sulfur species and reactive nitrogen oxides by dry deposition of sea-salt particles. Our estimation suggests that the upper limit of the scavenging rate of atmospheric sulfur species by sea-salt particles could rise to approximately 0.5 nmol m−2 day−1 at Syowa station during the summer. This value corresponded to about 30% of the concentration of particulate sulfur species such as non-sea-salt (nss)-SO2−4 and CH3SO−3 and ~10% of total atmospheric sulfur species (nss-SO2−4, CH3SO−3 and SO2). In contrast, the estimated NO−3 scavenging rate by sea-salt particles was ~0.2 nmol m−2 day−1, which is similar to the dry deposition rate of HNO3+N2O5 (approximately 0.2–0.3 nmol m−2 day−1). Hence, sea-salt particles probably play an important role as scavengers of acidic species in the coastal Antarctic regions.

Vertical variations of sea-salt modification in the boundary layer of spring Arctic during the ASTAR 2000 campaign

Abstract Airborne and ground-based aerosol/gas measurements were carried out in Svalbard between mid-March and mid-April 2000. From the viewpoint of vertical features of sea-salt modification in the lower troposphere (1500 m) of the Arctic spring, more than 1000 individual sea-salt particles were analyzed with scanning electron microscopy energy dispersive X-ray spectrometry (SEM-EDX) in the present study. Individual particle analysis suggested a vertical gradient of sea-salt modification in fine sea-salt particles with an altitude of 59–1485 m above sea level (asl), e.g. chlorine liberation rates of 33.0% (212 m asl) and 81.0% (1266 m asl) on 15 March, and 72.7% (100 m asl), 83.8% (495 m asl) and 95.8% (1411 m asl) on 26 March. Sea salts may be dominantly modified with SO2 and SO42− under Arctic haze conditions with higher SO2 concentration (≥2 nmol m−3), whereas they are dominantly modified with NO3− and reactive nitrogen oxides under Arctic background conditions, with [HNO3] of 0.15–1.3 nmol m−3 and [SO2] of 0.04–2 nmol m−3. Vertical trends in sea-salt modification suggested that it makes a significant contribution to the formation of reactive halogen species in the upper boundary layer and the lower free troposphere of the spring Arctic.

Transboundary secondary organic aerosol in western Japan indicated by the δ13C of water-soluble organic carbon and the m/z 44 signal in organic aerosol mass spectra.

The stable carbon isotope ratio (δ13C) of low-volatile water-soluble organic carbon (LV-WSOC) was measured in filter samples of total suspended particulate matter, collected every 24 h in the winter of 2010 at an urban site and two rural sites in western Japan. Concentrations of the major chemical species in fine aerosol (<1.0 μm) were also measured in real time by aerosol mass spectrometers. The oxidation state of organic aerosol was evaluated using f44; i.e., the proportion of the signal at m/z 44 (CO2+ ions from the carboxyl group) to the sum of all m/z signals in the organic mass spectra. A strong correlation between LV-WSOC and m/z 44 concentrations was observed, which suggested that LV-WSOC was likely to be associated with carboxylic acids in fine aerosol. Plots of δ13C of LV-WSOC versus f44 showed random variation at the urban site and systematic trends at the rural sites. The systematic trends qualitatively agreed with a simple binary mixture model of secondary organic aerosol with background LV-WSOC with an f44 of ∼0.08 and δ13C of -17‰ or higher. Comparison with reference values suggested that the source of background LV-WSOC was likely to be primary emissions associated with C4 plants.

“Sizing” Heterogeneous Chemistry in the Conversion of Gaseous Dimethyl Sulfide to Atmospheric Particles

The oxidation of biogenic dimethyl sulfide (DMS) emissions is a global source of cloud condensation nuclei. The amounts of the nucleating H2SO4(g) species produced in such process, however, remain uncertain. Hydrophobic DMS is mostly oxidized in the gas phase into H2SO4(g) + DMSO(g) (dimethyl sulfoxide), whereas water-soluble DMSO is oxidized into H2SO4(g) in the gas phase and into SO4(2-) + MeSO3(-) (methanesulfonate) on water surfaces. R = MeSO3(-)/(non-sea-salt SO4(2-)) ratios would therefore gauge both the strength of DMS sources and the extent of DMSO heterogeneous oxidation if Rhet = MeSO3(-)/SO4(2-) for DMSO(aq) + ·OH(g) were known. Here, we report that Rhet = 2.7, a value obtained from online electrospray mass spectra of DMSO(aq) + ·OH(g) reaction products that quantifies the MeSO3(-) produced in DMSO heterogeneous oxidation on aqueous aerosols for the first time. On this basis, the inverse R dependence on particle radius in size-segregated aerosol collected over Syowa station and Southern oceans is shown to be consistent with the competition between DMSO gas-phase oxidation and its mass accommodation followed by oxidation on aqueous droplets. Geographical R variations are thus associated with variable contributions of the heterogeneous pathway to DMSO atmospheric oxidation, which increase with the specific surface area of local aerosols.

Frost flowers and sea-salt aerosols over seasonal sea-ice areas in north-western Greenland during winter–spring

Sea salts and halogens in aerosols, frost flowers, and brine play an important role in atmospheric chemistry in polar regions. Simultaneous sampling and observations of frost flowers, brine, and aerosol particles were conducted around Siorapaluk in northwestern Greenland during December 2013 to March 2014. Results show that watersoluble frost flower and brine components are sea-salt components (e.g., Na, Cl, Mg2+, K, Ca2+, Br, and iodine). Concentration factors of sea-salt components of frost flowers and brine relative to seawater were 1.14–3.67. Sea-salt enrichment of Mg2+, K, Ca2+, and halogens (Cl, Br, and iodine) in frost flowers is associated with sea-salt fractionation by precipitation of mirabilite and hydrohalite. High aerosol number concentrations correspond to the occurrence of higher abundance of sea-salt particles in both coarse and fine modes, and blowing snow and strong winds. Aerosol number concentrations, particularly in coarse mode, are increased considerably by release from the sea-ice surface under strong wind conditions. Sulfate depletion by sea-salt fractionation was found to be limited in sea-salt aerosols because of the presence of non-sea-salt (NSS) SO2− 4 . However, coarse and fine sea-salt particles were found to be rich in Mg. Strong Mg enrichment might be more likely to proceed in fine seasalt particles. Magnesium-rich sea-salt particles might be released from the surface of snow and slush layer (brine) on sea ice and frost flowers. Mirabilite-like and ikaite-like particles were identified only in aerosol samples collected near new sea-ice areas. From the field evidence and results from earlier studies, we propose and describe sea-salt cycles in seasonal sea-ice areas.

Important contributions of sea-salt aerosols to atmospheric bromine cycle in the Antarctic coasts

Polar sunrise activates reactive bromine (BrOx) cycle on the Antarctic coasts. BrOx chemistry relates to depletion of O3 and Hg in polar regions. Earlier studies have indicated “blowing snow” as a source of atmospheric BrOx. However, surface O3 depletion and BrO enhancement occurs rarely under blowing snow conditions at Syowa Station, Antarctica. Therefore, trigger processes for BrOx activation other than the heterogeneous reactions on blowing snow particles must be considered. Results of this study show that enhancement of sea-salt aerosols (SSA) and heterogeneous reactions on SSA are the main key processes for atmospheric BrOx cycle activation. Blowing snow had Br− enrichment, in contrast to strong Br− depletion in SSA. In-situ aerosol measurements and satellite BrO measurements demonstrated clearly that a BrO plume appeared simultaneously in SSA enhancement near the surface. Results show that surface O3 depletion at Syowa Station occurred in aerosol enhancement because of SSA dispersion during the polar sunrise. Amounts of depleted Br− from SSA were matched well to the tropospheric vertical column density of BrO and BrOx concentrations found in earlier work. Our results indicate that SSA enhancement by strong winds engenders activation of atmospheric BrOx cycles via heterogeneous reactions on SSA.

Ambient fine and coarse particles in Japan affect nasal and bronchial epithelial cells differently and elicit varying immune response

Ambient particulate matter (PM) epidemiologically exacerbates respiratory and immune health, including allergic rhinitis (AR) and bronchial asthma (BA). Although fine and coarse particles can affect respiratory tract, the differences in their effects on the upper and lower respiratory tract and immune system, their underlying mechanism, and the components responsible for the adverse health effects have not been yet completely elucidated. In this study, ambient fine and coarse particles were collected at three different locations in Japan by cyclone technique. Both particles collected at all locations decreased the viability of nasal epithelial cells and antigen presenting cells (APCs), increased the production of IL-6, IL-8, and IL-1β from bronchial epithelial cells and APCs, and induced expression of dendritic and epithelial cell (DEC) 205 on APCs. Differences in inflammatory responses, but not in cytotoxicity, were shown between both particles, and among three locations. Some components such as Ti, Co, Zn, Pb, As, OC (organic carbon) and EC (elemental carbon) showed significant correlations to inflammatory responses or cytotoxicity. These results suggest that ambient fine and coarse particles differently affect nasal and bronchial epithelial cells and immune response, which may depend on particles size diameter, chemical composition and source related particles types.

Interactive effects of specific fine particulate matter compositions and airborne pollen on frequency of clinic visits for pollinosis in Fukuoka, Japan

Background: Previous studies have revealed the interactive effects of airborne pollen and particulate matter on the daily consultations for pollinosis, but it is uncertain which compositions are responsible. This study aimed to investigate the interactive effects of specific PM2.5 compositions and airborne pollen on the daily number of clinic visits for pollinosis in Fukuoka. Methods: We obtained daily data on pollen concentrations, PM2.5 compositions, PM2.5 mass, gaseous pollutants (SO2, NO2, CO, and O3), and weather variables monitored in Fukuoka between February and April, 2002–2012. In total, 73,995 clinic visits for pollinosis were made at 10 clinics in Fukuoka Prefecture during the study period. A time‐stratified case‐crossover design was applied to examine the interactive effects. The concentrations of PM2.5 and its compositions were stratified into low (<15th percentile), moderate (15th–85th percentile), and high (>85th percentile) levels, and the association between airborne pollen and daily clinic visits for pollinosis was analyzed within each level. Results: We found a significant interaction between specific PM2.5 compositions and airborne pollen. Specifically, the odds ratio of daily clinic visits for pollinosis per interquartile increase in pollen concentration (39.8 grains/cm2) at the average cumulative lag of 0 and 2 days during high levels of non‐sea‐salt Ca2+ was 1.446 (95% CI: 1.323–1.581), compared to 1.075 (95% CI: 1.067–1.083) when only moderate levels were observed. This result remained significant when other air pollutants were incorporated into the model and was fairly persistent even when different percentile cut‐off points were used. A similar interaction was found when we stratified the data according to non‐sea‐salt SO42‐ levels. This finding differed from estimates made according to PM2.5 and NO3‐ levels, which predicted that the effects of pollen were strongest in the lower levels. Conclusions: Associations between airborne pollen and daily clinic visits for pollinosis could be enhanced by high levels of specific PM2.5 compositions, especially non‐sea‐salt Ca2+. HighlightsSpecific PM2.5 compositions enhance the association between pollen and pollinosis.The effect of pollen was stronger during high concentrations of non‐sea‐salt Ca2+.Non‐sea‐salt Ca2+ and pollen act as a joint effect in promoting pollinosis symptoms.

Characteristics of sulfate haze over East Asia retrieved with satellite and ground-based remote sensing data

Optical observation around near UV spectral region potentially enables us to retrieve light absorbing features of aerosol, such as type as well as optical thickness. We analyzed near UV observation data to identify haze properties around Japan in the autumn of 2003, using Global Imager onboard Advanced Earth Observing Satellite-II (ADEOS-II/GLI), which has 380nm and 400nm window channels. At the same time, we had optical observation, such as a ground-based LIDAR measurement and a shipborne skyradiometer measurement, so as to retrieve vertical profile, particle sphericity, particle size distribution, and optical thickness of the haze. Based upon the three kinds of analyses with remotely sensed data, such as satellite, LIDAR, and skyradiometer, we have the following characteristics of the haze: little UV absorbing, of optical thickness 0.5 (around 500nm), within lower boundary layer (less than around 1km a.s.l.), and of spherical and fine particles (0.2 μm in radius). We also have some direct sampling measurements onboard Research Vessel Shirase, such as integrated nephelometer, particle soot / absorption photometer, and optical particle counter, so as to identify optical and microphysical properties of the haze as well as chemical composition analyses. The results of the surface direct sampling showed the dense haze dominantly consisted of smaller (0.2 μm in radius) and sulfate particulates, which is consistent to the remotely sensed results. Backward trajectory simulations also indicate that the hazy air mass had arrived from / through some mega cities over East Asia. Further, we are going to investigate the consistency between optical, microphysical, chemical, and dynamical aspects using a chemical transport model.