Published papers

We investigated the difference in the concentrations of air pollutants between the period of the Beijing 2008 Olympic Games and the same periods in the prior three years (2005-2007, the reference period), in particular, the chemical composition of the particulate matter. PM10, Black carbon (BC), SO2 and NO2 were reduced by 33%, 31%, 32% and 51%, respectively, whereas PM2.5 was not reduced during the Olympic period when compared to the reference period. Many pollution control measures that had been applied to prevent air pollution from contaminating the air quality in Beijing during the Olympic Games significantly reduced the larger particles (PM10), SO2 and NO2 but it did not as effectively reduce the much smaller particles (PM2.5). The sum of the measured water-soluble ions in total suspended particles (TSP) during the Olympic period was reduced by 35% when compared to the reference period. Each ion was reduced significantly by 43%-79% except for nitrogen-containing species. We estimated that CaSO4 reduction by 52% played a significant role in reducing larger particles during the Olympic period. Although many ions in PM2.5 showed a similar decreasing trend as those in TSP, NO3- in PM2.5 increased significantly. During the Olympic period, the atmospheric nitrogen cycle seemed to have been very complicated. Meteorological conditions such as temperature, relative humidity, or regional-scale air mass trajectory did not seem to be a major reason for the nitrate behavior. Instead, it is possible that the increase of ozone and/or oxidants around the center of Beijing may have accelerated the oxidation of nitrogen oxides to form nitrate. We found a trend in the concentration of high-molecular weight PAHs (HMW-PAHs), which had 5-7 rings decreased during the Olympic period. We considered that the reduction of HMW-PAHs that could be associated with the reduction of BC was due to the reduction of traffic flow resulting from traffic control measures implemented during that time period. © 2011 Elsevier Ltd.

Total suspended particulate (TSP) and particulate matter less than 2.5 μm in aerodynamic diameter (PM2.5) samples were collected over Xi'an for a 1-yr period to characterize the seasonal variations of water-soluble inorganic ions and to evaluate the effectiveness of the pollution policies and controls during the past 10 yr. Mass concentrations of five cations (sodium [Na+], potassium [K+], ammonium [NH4+], calcium [Ca2+], and magnesium [Mg2+]) and four anions (fluoride [F-], chloride [Cl-], nitrate [NO3-], and sulfate [SO42-]) were determined by ion chromatography. The yearly arithmetic-mean mass concentrations of the total measured water-soluble ions in TSP and PM2.5 were 83.9 ± 58.4 and 45 ± 34.3 μg · m-3. The most abundant ions in TSP were SO42-, NO3-, Ca2+, and NH4+; whereas in PM2.5 the dominant ions were SO42-, NH4+, and NO3-. Most of the ions were more concentrated in the PM2.5 than in TSP, but two exceptions were Ca2+ and Mg2+. Comparisons of the molar ratios of Mg2+/Ca2+ in TSP indicated that fugitive dust was the main source for these two ions, and the influence of soil dust from outside of the city was most evident during dust storms. The mass concentrations of SO42-, NO3-, NH4+, and K+ in TSP were highest in winter and lowest in spring, but Ca2+ was much higher in spring than other seasons because of suspended mineral dust. In PM2.5, NO3- and K+ also showed winter maxima, but SO4 2- and NH4+ were highest in summer. Calculations of ion equivalents showed that TSP samples were more alkaline than PM2.5, the latter being weakly acidic in winter and autumn. High sulfur and nitrogen oxidation ratios occurred in summer and autumn, and there was evidence for the formation of ammonium bisulfate in TSP, ammonium sulfate in PM2.5, and ammonium nitrate in both fractions. Comparisons with the results of prior studies indicate that pollution controls in Xi'an have reduced the levels of air pollution over the past 10 yr. The SO42- concentration during the heating season in 2006 was only about one-eighth of that in 1996, and NH4+ decreased to one-ninth of that in 1996. Seasonal variations in the NO3 -/SO42- ratio are different than the patterns observed 10 yr ago, suggesting that emission sources have changed, with those from motor vehicles becoming increasingly important. Copyright 2008 Air & Waste Management Association.

Daily observations of hazardous trace metal concentrations in aerosols in Beijing, China were made in the period from 2001 to 2006. We considered coal combustion as a major source of some anthropogenic metals by achieving a correlation analysis and by investigating enrichment factors and relative composition of metals. A possible extra source of some specific metals, such as Cu and Sb, was brake abrasion particles, however, we did not think the transport-related particle was a major source for the hazardous anthropogenic metals even though they could originate from vehicle exhaust and brake/tire abrasion particles. A time-trend model was used to describe temporal variations of chemical constituent concentrations during the five-year period. Several crustal elements, such as Al, Ti, V, Cr, Mn, Fe, and Co, did not show clear increases, with annual rates of change of -15.2% to 3.6%. On the other hand, serious increasing trends were noted from several hazardous trace metals. Cu, Zn, As, Cd, and Pb, which are derived mainly from anthropogenic sources, such as coal combustion, showed higher annual rate of change (4.9-19.8%, p < 0.001) according to the regression model. In particular, the Cd and Pb concentrations increased remarkably. We hypothesize that the trend towards increasing concentrations of metals in the air reflects a change that has occurred in the process of burning coal, whereby the use of higher temperatures for coal combustion has resulted in increased emissions of these metals. The increasing use of low-rank coal may also explain the observed trends. In addition, nonferrous metal smelters are considered as a potential, albeit minor, reason for the increasing atmospheric concentrations of anthropogenic hazardous metals in Beijing city. © 2008 Elsevier Ltd. All rights reserved.

This study investigates the source identification of nickel in the aerosol of the Tokyo metropolitan area. TSP and PM2.5 samples were collected daily from August to November 2004. The samples were examined by means of the water-extraction method, followed by elemental analysis and SEM/EDX analysis. We distinguished two types of atmospheric nickel sources in the studied area: (1) particles derived from heavy oil combustion, distributed mostly in fine particles such as PM2.5, relatively water-soluble, and containing vanadium and (2) particles derived from mechanical abrasion/erosion of metallic surfaces, distributed in coarse particles such as TSP, relatively water-insoluble, and containing chromium. © 2007 Elsevier Ltd. All rights reserved.

We developed a useful analytical method for the determination of polycyclic aromatic hydrocarbons (PAH) concentrations in the aerosol of China. We used an accelerated solvent extraction (ASE) method for the extraction of PAHs from the aerosol samples, in order to reduce the extraction time and the solvent volume used. The optimum purification method was developed, with aminopropylsilane chemically-bonded stationary-phase column chromatography, in order to remove many co-extractives which cannot be removed by conventional purification methods using silica-gel column chromatography. HPLC/fluorescence detection (FLD) was adopted as the analytical method, because it has very high sensitivity to PAH and it is easy to install, operate, and maintain as compared with GC/MS. With the analytical method developed in this study, the recovery and precision (RSD) for most of the PAHs ranged from 75% to 129% and from 2.8% to 22.7%, respectively. The concentrations of PAHs in the aerosol samples collected from October 2003 to April 2005 in Beijing, China were determined using the newly developed method. ∑PAHs, which is the sum of the concentrations of all detected PAHs, was 177.8 ± 239.9 ng m-3 (n = 64). The ∑PAHs concentration in the heating season (305.1 ± 279.0 ng m-3, n = 33) was 7.2 times higher than that in the non-heating season (42.3 ± 32.0 ng m-3, n = 31). These strong seasonal variations in atmospheric PAH concentration are possibly due to coal combustion for residential heating in winter. © 2006 Elsevier Ltd. All rights reserved.

The most prevalent pollutant, polycyclic aromatic hydrocarbons (PAHs) is now plenteously distributed in the global atmosphere. We recently quantified 36 polycyclic aromatic hydrocarbons (PAHs) associated with aerosols (particulate matter: PM) in five Asian cities: Tokyo (Japan), Beijing (China), Kolkata (India), Hanoi (Vietnam), and Kuala Lumpur (Malaysia). Average atmospheric PAH concentrations (∑12 PAHs-ng m–3) increased in the order of Kuala Lumpur (2.99) ≈ Tokyo (3.95) < Hanoi (7.99) << Kolkata (63.5) << Beijing (142.8). The most abundant PAHs in PM samples in these cities were chrysene, benz[a]anthracene, benzofluoranthenes, benzo[a]pyrene, and benzo[e]pyrene. We used the PAH compositions, especially the relative abundances of alkylated PAHs, and hopanes to determine vehicle exhaust-derived PAHs, and levoglucosan as a tracer for biomass burning, especially from wood combustion. Vehicle exhaust contributed to atmospheric PAHs in all cities, indicated by higher ratios of (C3017α)/total PAHs and MPAHs/PAHs than coal and wood combustion products. Coal combustion contributed also in winter aerosols in Beijing, indicated by higher abundance of β isomers i.e., 17β21β (H)-C30hopane (C3017β) and 17β21β (H)-C29hopane (C2917β) signifying mass use of coal for heating. The ratio of levoglucosan/PAHs was high in Kuala Lumpur and Hanoi, suggesting greater inputs of PAHs from biomass burning there.

The allergic inflammatory effects of particulate matter (PM) 2.5, collected with the cyclone system in Yokohama city in Japan, were investigated in NC/Nga mice, which are hypersensitive to mite allergens. PM2.5 with alum was injected intraperitoneally for sensitization. Five days later, 200 μg of PM2.5 in 25 μL of saline was administered to mice intranasally five times for further sensitization. On the 11th day, PM2.5 was administered as a challenge. On the 12th day, mice were examined for airway hyperresponsiveness (AHR), the bronchoalveolar lavage fluid (BALF) cell count, mRNA expression of Th1, Th2 cytokines, and metallothioneins in lung tissue, and histopathology. PM2.5 increased AHR, total cell numbers including eosinophils in BALF, and mRNA levels of IL-5, IL-22, eotaxin, eotaxin 2, and metallothionein 3. In PM2.5-induced lungs, inflammation was observed around the bronchus. These results demonstrate that PM2.5 alone, collected with the cyclone system in Yokohama city in Japan, induces asthma-like airway inflammation. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1047–1054, 2017.

Chlorinated polycyclic aromatic hydrocarbons (ClPAHs) are novel species of environmental contaminants whose possible sources remain unclear. The occurrence of ClPAHs within total suspended particles (TSP) is compared with weekly air samples at two sites of differing characteristics (industrial and residential) in the megacity of Nagoya, Japan. Samples were collected over 12 months during 2011-2012. All 24 species of targeted ClPAHs were detected at both industrial and residential sites, where mean concentrations of total ClPAHs in TSP were 20.7 and 14.1 pg/m3, respectively. High concentrations at the industrial site were frequently observed during winter, suggesting potent seasonal ClPAH sources there. Positive matrix factorization modeling of particulate ClPAH source identification and apportioning were conducted for datasets including ClPAHs, PAHs, elements and ions, plus elemental carbons in TSP. Eight factors were identified as possible ClPAH sources, with estimates that the dominant one was a specific source of ClPAH emission (31%), followed by traffic (23%), photodegradable and semi-volatile species (18%), long-range transport (11%), and industry and oil combustion (10%). Source contributions of ClPAHs differed substantially from those of PAHs. This suggests specific and/or potent ClPAH sources in the local area, and that the production mechanisms between ClPAHs and PAHs are substantially different.

This study focused on the measurement of the actual charging state of ambient aerosol particles, which is important for understanding the intricate process of adverse health effects caused by particulate matter (PM). The net electrostatic charging state of PM2.5 collected on filter media was measured in this study. The Faraday cage method and surface potential measurements were used in this study. The results showed that the polarities of the net charging state measured using these two methods were in agreement for 42 out of 48 samples (87.5%), and 36 samples (75%) were negatively charged. The filters were not significantly charged by friction between the filters and air not containing PM. Charge addition to or leakage from the filters was not observed over a two-month storage period. Net charging state of PM2.5 collected on the filters was concluded to be negative in most cases, based on data's support of the assumption that aerosol charging state is not altered by the process of PM collection using filter.

© 2020 A PM2.5 high-volume impactor (HVI) sampler is developed, which has a flow rate of 1130 L per minute (lpm) (1.13 m3/min) and in it, the filter size used is of 8 inch × 10 inch. The major advantages of this sampler as compared to other low-volume sampler (flow rate 16.67 lpm) are lower uncertainty in mass measurement, higher PM2.5 mass collection and lesser sampling time. To develop this PM2.5 HVI sampler, a series of simulation and experimental studies were carried out. The optimized D50 cutoff size of 2.52 μm was obtained experimentally under real ambient conditions (i.e. with polydisperse ambient particles) after the parametric adjustments. The commercial PM2.5 HV sampler cutoff size was also evaluated experimentally, and agreed well to the D50 cutoff size of developed PM2.5 HVI sampler. Field performance studies of developed PM2.5 HVI sampler were also carried out under both high- and low- particle mass loading conditions along with commercial PM2.5 high- and low-volume samplers. The developed PM2.5 HVI sampler agreed well with commercial PM2.5 high- and low-volume samplers, i.e. PM2.5 HVS, BAM and WINS reference sampler in mass measurement with mean deviations of 12.7, 18.5 and 11.7 μg/m3 (i.e. 5.05, 4.86 and 3.70%), respectively under tested conditions. This PM2.5 HVI sampler is very useful especially where the extensive offline chemical analysis of filter samples/high amount of particulate material is needed for source apportionment studies or analysis of bioassay or toxicological purposes (in vitro/in vivo studies), diurnal studies, and air sampling where the mass concentration of particles is very low, e.g. marine, polar regions, most of the rural sites, etc.

The aerosol oxidative potential (OP) is considered to better represent the acute health hazards of aerosols than the mass concentration of fine particulate matter (PM2.5). The proposed major contributors to OP are water soluble transition metals and organic compounds, but the relative magnitudes of these compounds to the total OP are not yet fully understood. In this study, as the first step toward the numerical prediction of OP, the cumulative OP (OPtm*) based on the top five key transition metals, namely, Cu, Mn, Fe, V, and Ni, was defined. The solubilities of metals were assumed constant over time and space based on measurements. Then, the feasibility of its prediction was verified by comparing OPtm* values based on simulated metals to that based on observed metals in East Asia. PM2.5 typically consists of primary and secondary species, while OPtm* only represents primary species. This disparity caused differences in the domestic contributions of PM2.5 and OPtm*, especially in large cities in western Japan. The annual mean domestic contributions of PM2.5 were 40%, while those of OPtm* ranged from 50 to 55%. Sector contributions to the OPtm* emissions in Japan were also assessed. The main important sectors were the road brake and iron–steel industry sectors, followed by power plants, road exhaust, and railways.

Background: A recent epidemiological study showed that air pollution is closely involved in the prognosis of ischemic stroke. We and others have reported that microglial activation in ischemic stroke plays an important role in neuronal damage. In this study, we investigated the effects of urban aerosol exposure on neuroinflammation and the prognosis of ischemic stroke using a mouse photothrombotic model. Results: When mice were intranasally exposed to CRM28, urban aerosols collected in Beijing, China, for 7 days, microglial activation was observed in the olfactory bulb and cerebral cortex. Mice exposed to CRM28 showed increased microglial activity and exacerbation of movement disorder after ischemic stroke induction. Administration of core particles stripped of attached chemicals from CRM28 by washing showed less microglial activation and suppression of movement disorder compared with CRM28-treated groups. CRM28 exposure did not affect the prognosis of ischemic stroke in null mice for aryl hydrocarbon receptor, a polycyclic aromatic hydrocarbon (PAH) receptor. Exposure to PM2.5 collected at Yokohama, Japan also exacerbated movement disorder after ischemic stroke. Conclusion: Particle matter in the air is involved in neuroinflammation and aggravation of the prognosis of ischemic stroke; furthermore, PAHs in the particle matter could be responsible for the prognosis exacerbation.

Charge distribution measurements are required to understand the spatiotemporal distribution of the number concentrations of submicron atmospheric particles that affect radiative forcing and particle deposition in human airways. The number concentrations of non-charged and charged particles within the 0.3–0.5 μm diameter (D) range were measured at Keio University in Yokohama, Japan, from June 2022 to January 2023 by combining a parallel-pate particle separator and optical particle counters to investigate critical parameters controlling the charging state of submicron atmospheric particles. The measurement uncertainties in the average charge number per particle (pave) and the standard deviation (1σ), derived from the charge distribution of the submicron particles, were within 15%. The monthly median values of 1σ increased in summer and decreased in winter and correlated with the water vapor amount and wind speed. The 1σ values in summer and winter, derived from the seasonally averaged charge distributions of particles, were close to those from the theoretically calculated charge distribution of particles within 0.387–0.5 μm D range and with D = 0.3 μm, respectively, suggesting that the observed particle charge distributions approached the stationary charge distribution for the effective D. In summer, the frequent transport of water molecules and ions from the Pacific Ocean causes efficient collisions between multiple ions and submicron particles with a larger effective D, which may expand the charge distribution of particles. The polarity ratio, the concentration of positively charged particles relative to that of negatively charged particles, was almost unity, indicating the well-balanced charge polarity of the submicron atmospheric particles. The polarity ratio and pave changed significantly during lightning events, indicating that the atmospheric particle charge balance broke. Our findings show that the charge distribution of submicron atmospheric particles can be partly controlled by meteorological parameters (e.g., absolute humidity) and the microphysical properties of the particles.

The Fukushima Daiichi Nuclear Power Plant accident in Japan resulted in the emission of many radioactive cesium (Cs)-containing particles that have charges on the surface due to self-charging. Charged aerosol particles are efficiently deposited inside human airways, leading to adverse health effects. To evaluate these effects, we developed a technique for estimating the charge number (n p) of radioactive particles by measuring the surface potentials (V p) of individual radioactive particles using Kelvin probe force microscopy. The V p values of the individual CsCl particles were highly correlated with the surface n p, indicating that V p is a measure of the charged aerosol state. To further examine the V p–n p relationship, a simplified capacitance model was developed to estimate the ratio of V p to n p per unit area of particles. Although the calculated V p was proportional to the n p, consistent with our experiment, the calculated ratio was higher than those determined experimentally. The magnitude of this ratio may depend on the conductivity, microphysical properties and chemical composition of the particles. Despite these uncertainties, the experimentally determined V p–n p relationship of the CsCl particles was used to estimate the n p of the radioactive and non-radioactive particles from the measurement of the V p of these particles. It was demonstrated that the n p of the radioactive particles was much higher than that of the non-radioactive particles, suggesting that radioactive particles are efficiently charged by self-charging. These charged radioactive particles may strongly cause adverse human health effects owing to their efficient deposition in human airways.

This article aims to showcase recent advancements in aerosol research, focusing on their applications in various fields, from environmental health to infectious disease control. The work presented here stems from our research group’s mission to improve global public health through cutting-edge studies on the effects of ambient air and other environmental media on human health. This article will introduce several key developments, including: a novel method for evaluating the health effects of particulate matter using cyclones and water-soluble filters; techniques for particle measurement in enclosed environments; insights into the charging state of ambient submicron particles; and innovative particle measurement technologies contributing to infectious disease control.

Particulate matter is the primary pollutant of the urban atmosphere in Beijing. PM10 was 60% higher than the national second-class standard in 2006. Based on fast-response aerosol concentrations and elemental compositions in daily TSP, this study revealed the regionality of episodic aerosol pollution. First, surface weather patterns indicated that episodic aerosol pollution was affected by the passing of cold fronts caused by the synoptic cycles covering large areas, which naturally resulted in the regionality of aerosol pollution in Beijing. Second, as the episodes progressed, PM2.5/PM10 and Pb/Al increased, which was associated with the removal of coarse particles, nucleation of nanoparticles, and formation of secondary particles. Thus aerosol became finer and aged, which implies that the aerosol in Beijing is a result of regional sources.

Polycyclic aromatic hydrocarbons (PAHs) are major air pollutants that are ubiquitously produced by the combustion of organic materials, and it is extremely important to identify their pollution sources. In this study, molecular fingerprinting and compound class-specific radiocarbon dating (CCSRA) were performed on PAHs from canal sediments and air samples collected in Kolkata, India’s third largest city (population approximately 16 million), where PAHs pollution has been a serious problem. Average PAH (Σ12-parent PAHs) concentrations in air samples were 65.1 ng m–3 in summer and 70.9 ng m–3 in winter and in canal sediments were 32.7 μg g–1, which are classified as “very high-level” pollution. Molecular fingerprinting using methyl-PAH/PAH (MPAHs/PAHs) ratios and isomer pair ratios with molecular weights of 178, 202, 228, and 276 suggested that wood and coal combustion were the dominant sources of PAHs in the sediment, and that atmospheric PAHs were influenced by oil combustion in addition to them. The fraction of contemporary carbon (ƒC) of sedimentary PAHs (0.056–0.100), together with the extremely low MPAHs/PAHs ratio results, lead to the conclusion that the major source of the high concentration of PAHs in the canals is from coal combustion. On the other hand, the ƒC of atmospheric PAHs (0.272–0.369) was close to the share of biomass fuels in India’s domestic fuel consumption in 2011 (about 35%). Furthermore, the observed ƒC-discrepancy between atmospheric and sedimentary PAHs in the same urban environment was interpreted to give an insight into the loading pathway of PAHs to canal sediments in Kolkata.

Seasonal powder samples of PM2.5 in Xi'an City were collected in this study based on the large flow cyclone impact sampler. By measuring the oxidative potential (OP) of water-soluble and water-insoluble phases, as well as the inorganic elements, water-soluble ions, carbon components, and organic functional groups in PM2.5, the contribution of water-soluble/water-insoluble phases to OP were revealed and the impacts of chemical components on OP were discussed. The results showed that the total OP of PM2.5 in Xi'an was significantly higher in autumn and winter (7.24 and 5.19µmol/(min·mg) in autumn and winter, respectively) than in spring and summer (2.06 and 3.15µmol/(min·mg) in spring and summer, respectively). The OP of PM2.5 in spring and summer were mainly contributed by water-soluble phase (averagely 70.0%), instead of water-insoluble phase (averagely 73.9%) in autumn and winter. Water-soluble metals, especially heavy metals such as Ni, Pb, Ba, Mn, Cu and Ti, (0.602.5 samples.

Transboundary air pollutants have raised serious health concerns, particularly in regions with minimal local pollution sources. Distinguishing between local pollution and transboundary contributions is crucial for accurately assessing the health risks to local populations. This study aimed to analyze the differences in coarse and fine particulate matter and develop methods to obtain exposure data for epidemiological studies, thereby providing a scientific basis for public health interventions. We collected SPM-PM2.5 (physically excluded PM2.5 from SPM) and PM2.5 samples in Yonago City, a coastal urban area in Tottori Prefecture, Japan, from 19 October 2015 to 25 July 2016 using a novel slit jet impactor (MCAS-SJ). Positive matrix factorization analysis used heavy metal, ion, and carbon concentrations to identify pollutant sources. This study identified four major air pollution events during the sampling period, primarily attributed to transboundary transport. Episode I was dominated by nitric aerosols, Episodes II and III by Asian dust, and Episode IV by sulfate aerosols. An analysis using global chemical transport models and backward trajectories confirmed that these events verified the contribution of transboundary pollution. In conclusion, identifying the impact of transboundary pollution on local air quality enables an accurate risk assessment of populations. This study provides scientific evidence for developing effective public health strategies and preventive measures. Additionally, the methodology used in this study holds the potential for international contributions and future research applications, helping to address air pollution challenges on a broader scale.