Source contribution of black carbon aerosol during 2020-2022 at an urban site in Indo-Gangetic Plain.

The extensive emissions of black carbon (BC) from the Indo-Gangetic Plain (IGP) region of India have been well recognized. Particularly, biomass emissions from month-specific crop-residue burning (April, May, October, November) and heating activities (December-February) are considered substantial contributors to BC emissions in the IGP. However, their precise contribution to ambient BC aerosol has not been quantified yet and remains an issue of debate. Therefore, this study aims to fill this gap by quantifying the contribution of these month-specific biomass emissions to ambient BC at an urban site in IGP. This study presents the analysis of BC mass concentrations (MBC) measured for 3 years (2020-2022) in Delhi using an optical photometer i.e., continuous soot monitoring system (COSMOS). A statistical analysis of monthly mean MBC and factors affecting the MBC (ventilation coefficients, air mass back trajectories, fire counts) is performed to derive month-wise contribution due to background concentration, conventional emission, regional transport, crop-residue burning, and heating activities. The yearly mean MBC (5.3 ± 4.7, 5.6 ± 5.0, and 5.3 ± 3.5 µg m-3 during 2020, 2021, and 2022, respectively) remained relatively consistent with repetitive monthly patterns in each year. The peak concentrations were observed from November to January and low concentrations from June to September. Anthropogenic activities contributed significantly to MBC over Delhi with background concentration contributing only 30 % of observed MBC. The percentage contribution of emissions from crop-residue burning varied from 15 % (May) to 37 % (November), while the contribution from heating activities ranged from 25 % (December) to 39 % (January). This source quantification study highlights the significant impact of month-specific biomass emissions in the IGP and can play a vital role in better management and control of these emissions in the region.

Contributions of long-range transport from the Asian continent and local emissions on atmospheric PM2.5, polycyclic aromatic hydrocarbons, and their nitro-derivatives in Kanazawa and Noto Peninsula, Japan.

This study collected samples of particulate matter that are 2.5 µm or less in diameter (PM2.5) in Kanazawa, Japan, and Noto Peninsula located 100 km north on the windward side of the westerlies from the Asian continent and characterized the extent of polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs (NPAHs) pollution in Kanazawa. Emission areas and specific sources of PM2.5 and of PAHs and NPAHs were clarified via back-trajectory analysis and the NP-method, respectively. The results indicate that during 2020 and 2021, most PAHs (93%) in Kanazawa were transported from the Asian continent by westerlies and that the main source was coal and biomass combustion. The presence of NPAHs in Kanazawa was caused by a mixture of transport from the Asian continent (53%) and local emissions (47%), with the main source of the latter being from vehicles. Although the content of combustion-derived particulates (Pc) was <2.4% of PM2.5 in Kanazawa, this showed a similar seasonal variation (winter > summer) to that of PAHs. The contribution of Pc transported from the Asian continent exceeded that of locally emitted Pc. The current situation of Kanazawa is considerably different from that of 1997, when local vehicles were the main source of pollution.

Source apportionment of anthropogenic and biogenic organic aerosol over the Tokyo metropolitan area from forward and receptor models.

Organic aerosol (OA) is a dominant component of PM2.5, and accurate knowledge of its sources is critical for identification of cost-effective measures to reduce PM2.5. For accurate source apportionment of OA, we conducted field measurements of organic tracers at three sites (one urban, one suburban, and one forest) in the Tokyo Metropolitan Area and numerical simulations of forward and receptor models. We estimated the source contributions of OA by calculating three receptor models (positive matrix factorization, chemical mass balance, and secondary organic aerosol (SOA)-tracer method) using the ambient concentrations, source profiles, and production yields of OA tracers. Sensitivity simulations of the forward model (chemical transport model) for precursor emissions and SOA formation pathways were conducted. Cross-validation between the receptor and forward models demonstrated that biogenic and anthropogenic SOA were better reproduced by the forward model with updated modules for emissions of biogenic volatile organic compounds (VOC) and for SOA formation from biogenic VOC and intermediate-volatility organic compounds than by the default setup. The source contributions estimated by the forward model generally agreed with those of the receptor models for the major OA sources: mobile sources, biomass combustion, biogenic SOA, and anthropogenic SOA. The contributions of anthropogenic SOA, which are the main focus of this study, were estimated by the forward and receptor models to have been between 9 % and 15 % in summer 2019. The observed percent modern carbon data indicate that the amounts of anthropogenic SOA produced during daytime have substantially declined from 2007 to 2019. This trend is consistent with the decreasing trend of anthropogenic VOC, suggesting that reduction of anthropogenic VOC has been effective in reducing anthropogenic SOA in the atmosphere.

Role of oxides of nitrogen in the ozone-cardiorespiratory visit association.

Ozone (O3)-induced health effects vary in terms of severity, from deterioration of lung function and hospitalization to death. Several studies have reported a linear increase in health risks after O3 exposure. However, current evidence suggests a non-linear U- and J-shaped concentration-response (C-R) function. The potential increasing risks with decreasing O3 concentrations may seem counterintuitive from the traditional standpoint that decreasing exposure should lead to decreasing health risks. Tus, the question of whether the increasing risks with decreasing concentrations are truly O3-induced or might be from other C-R mechanisms. If these potential risks were not accounted for, this may have contributed to the risks observed at the low ozone concentration range. In this study, we examined the short-term effects of photochemical oxidant (Ox, parts per billiion) on outpatient cardiorespiratory visits in 21 Japanese cities after adjusting for other air pollutant-specific C-R functions. Daily cardiorespiratory visits from January 1, 2014 to December 31, 2016 were obtained from the Japanese Medical Data Center Co. Ltd. Similar period of meteorological and air pollution variables were obtained from relevant data sources. We utilized a time-stratified case crossover design coupled with the generalized additive mixed model (TSCC-GAMM) to estimate the association between Ox and cardiorespiratory outpatient visits, after adjusting for several covariates. A total of 2,588,930 visits were recorded across the study period, with a mean of 111.87 and a standard deviation of 138.75. The results revealed that crude Ox-cardiorespiratory visits exhibited a U-shaped pattern. However, adjustment of the oxides of nitrogen, particularly nitrogen monoxide (NO), attenuated the lower risk curve and subsequently altered the shape of the C-R function, with a substantial reduction observed during winter. NO- and nitrogen dioxide (NO2)-adjusted Ox-cardiorespiratory associations increased nearly linearly, without an apparent threshold. Current evidence suggests the importance of adjusting the oxides of nitrogen in estimating the Ox C-R risk functions.

Long-term trends in mortality risk associated with short-term exposure to air pollution in 10 Japanese cities between 1977 and 2015.

BACKGROUND AND AIM: Short-term associations between air pollution and mortality have been well reported in Japan, but the historical changes in mortality risk remain unknown. We examined temporal changes in the mortality risks associated with short-term exposure to four criteria air pollutants in selected Japanese cities. METHODS: We collected daily mortality data for non-accidental causes (n = 5,748,206), cardiovascular (n = 1,938,743) and respiratory diseases (n = 777,266), and air pollutants (sulfur dioxide [SO2], nitrogen dioxide [NO2], suspended particulate matter [SPM], and oxidants [Ox]) in 10 cities from 1977 to 2015. We performed two-stage analysis with 5-year stratification to estimate the relative risk (RR) of mortality per 10-unit increase in the 2-day moving average of air pollutant concentrations. In the first stage, city-specific associations were assessed using a quasi-Poisson generalized linear regression model. In the second stage, city-specific estimates were pooled using a random-effects meta-analysis. Linear trend and ratio of relative risks (RRR) were computed to examine temporal changes. RESULTS: When stratifying the analysis by every 5 years, average concentrations in each sub-period decreased for SO2, NO2, and SPM (14.2-2.3 ppb, 29.4-17.5 ppb, 52.1-20.6 µg/m3, respectively) but increased for Ox (29.1-39.1 ppb) over the study period. We found evidence of a negative linear trend in the risk of cardiovascular mortality associated with SPM across sub-periods. However, the risks of non-accidental and respiratory mortality per 10-unit increase in SPM concentration were significantly higher in the most recent period than in the earliest period. Other gaseous pollutants did not show such temporal risk change. The risks posed by these pollutants were slightly to moderately heterogeneous in the different cities. CONCLUSIONS: The mortality risks associated with short-term exposure to SPM changed, with different trends by cause of death, in 10 cities over 39 years whereas the risks for other gaseous pollutants were relatively stable.

Maternal Exposure to Fine Particulate Matter and Its Chemical Components Increasing the Occurrence of Gestational Diabetes Mellitus in Pregnant Japanese Women.

Introduction: PM2.5 exposure is a suspected risk factor for diabetes. It is hypothesized that maternal PM2.5 exposure contributes to the development of gestational diabetes mellitus (GDM). The association between PM2.5 exposure and GDM is controversial and limited evidence is available for the exposure to PM2.5 chemical components. We investigated the association between maternal exposure to total PM2.5 mass and its components, particularly over the first trimester (early placentation period), and GDM. Methods: Data were obtained from the Japan Perinatal Registry Network database, which includes all live births and stillbirths after 22 weeks of gestation at 39 cooperating hospitals in 23 Tokyo wards (2013-2015). At one fixed monitoring site, we performed daily filter sampling of fine particles and measured daily concentrations of carbon and ion components. The average concentrations of total PM2.5 and its components over the 3 months before pregnancy and the first (0-13 gestational weeks) and second (14-27 gestational weeks) trimesters were calculated and assigned to each woman. We estimated the odds ratios (ORs) of GDM in a multilevel logistic regression model. Results: Among 82,773 women (mean age at delivery = 33.7 years) who delivered singleton births, 3,953 (4.8%) had GDM. In the multiexposure period model, an association between total PM2.5 exposure and GDM was observed for exposure over the first trimester (OR per interquartile range (IQR = 3.63 µg/m3) increase = 1.09; 95% confidence interval (CI) = 1.02-1.16), but not for the 3 months before pregnancy or the second trimester. For PM2.5 components, only organic carbon exposure over the first trimester was positively associated with GDM (OR per IQR (0.51 µg/m3) increase = 1.10; 1.00-1.21). Conclusions: This is the first evidence that exposure to total PM2.5 and one of its components, organic carbon, over the first trimester increases GDM occurrence in Japan.

A Case-Crossover Analysis of the Association between Exposure to Total PM2.5 and Its Chemical Components and Emergency Ambulance Dispatches in Tokyo.

A limited number of studies have investigated the association between short-term exposure to PM2.5 components and morbidity. The present case-crossover study explored the association between exposure to total PM2.5 and its components and emergency ambulance dispatches, which is one of the indicators of morbidity, in the 23 Tokyo wards. Between 2016 and 2018 (mean mass concentrations of total PM2.5 13.5 µg/m3), we obtained data, from the Tokyo Fire Department, on the daily cases of ambulance dispatches. Fine particles were collected at a fixed monitoring site and were analyzed to estimate the daily mean concentrations of carbons and ions. We analyzed 1038301 cases of health-based all-cause ambulance dispatches by using a conditional logistic regression model. The average concentrations of total PM2.5 over one and the previous day were positively associated with the number of ambulance dispatches. In terms of PM2.5 components, the percentage increase per interquartile range (IQR) increase was 0.8% for elemental carbon (IQR = 0.8 µg/m3; 95% CI = 0.3-1.3%), 0.9% for sulfate (2.1 µg/m3; 0.5-1.4%), and 1.1% for ammonium (1.3 µg/m3; 0.4-1.8%) in the PM2.5-adjusted models. This is the first study to find an association between some specific components in PM2.5 and ambulance dispatches.

Aerosol Proteinaceous Matter in Coastal Okinawa, Japan: Influence of Long-Range Transport and Photochemical Degradation.

The characteristics, sources, and atmospheric oxidation processes of marine aerosol proteinaceous matter (APM), including total proteins and free amino acids (FAAs), were investigated using a set of 1 year total suspended particulate (TSP) samples collected in the coastal area of Okinawa Island in the western North Pacific rim. The concentrations of APM at this site (total proteins: 0.16 ± 0.10 µg m-3 and total FAAs: 9.7 ± 5.6 ng m-3, annual average) are comparable to those of marine APM. The major FAA species of APM are also similar to previously reported marine APM with glycine as the dominant species (31%). Based on the different seasonal trends and weak correlations of total proteins and FAAs, we found that they were contributed by different sources, especially with the influence of long-range transport from the Asian continent of northern China and Mongolia and the oceanic area of the Bohai Sea, Yellow Sea, and East China Sea. The photochemical oxidation processes of high-molecular-weight proteins releasing FAAs (especially glycine) were also considered as an important factor influencing the characteristics of APM at this site. In addition, we propose a degradation process based on the correlation with ozone and ultraviolet radiation, emphasizing their roles in the degradation of proteins. Our findings help to deepen the understanding of atmospheric photochemical reaction processes of organic aerosols.

Exposure to chemical components of fine particulate matter and ozone, and placenta-mediated pregnancy complications in Tokyo: a register-based study.

BACKGROUND: Maternal exposure to fine particulate matter (PM2.5) was associated with pregnancy complications. However, we still lack comprehensive evidence regarding which specific chemical components of PM2.5 are more harmful for maternal and foetal health. OBJECTIVE: We focused on exposure over the first trimester (0-13 weeks of gestation), which includes the early placentation period, and investigated whether PM2.5 and its components were associated with placenta-mediated pregnancy complications (combined outcome of small for gestational age, preeclampsia, placental abruption, and stillbirth). METHODS: From 2013 to 2015, we obtained information, from the Japan Perinatal Registry Network database, on 83,454 women who delivered singleton infants within 23 Tokyo wards (≈627 km2). Using daily filter sampling of PM2.5 at one monitoring location, we analysed carbon and ion components, and assigned the first trimester average of the respective pollutant concentrations to each woman. RESULTS: The ORs of placenta-mediated pregnancy complications were 1.14 (95% CI = 1.08-1.22) per 0.51 µg/m3 (interquartile range) increase of organic carbon and 1.11 (1.03-1.18) per 0.06 µg/m3 increase of sodium. Organic carbon was also associated with four individual complications. There was no association between ozone and outcome. SIGNIFICANCE: There were specific components of PM2.5 that have adverse effects on maternal and foetal health.

Maternal exposure to fine particulate matter over the first trimester and umbilical cord insertion abnormalities.

BACKGROUND: Our hypothesis was that exposure to fine particulate matter (PM2.5) is related to abnormal cord insertion, which is categorized as a form of placental implantation abnormality. We investigated the association between exposure to total PM2.5 and its chemical components over the first trimester and abnormal cord insertion, which contributes to the occurrence of adverse birth outcomes. METHODS: From the Japan Perinatal Registry Network database, we used data on 83 708 women who delivered singleton births at 39 cooperating hospitals in 23 Tokyo wards (2013-2015). We collected PM2.5 on a filter and measured daily concentrations of carbon and ion components. Then, we calculated the average concentrations over the first trimester (0-13 weeks of gestation) for each woman. A multilevel logistic-regression model with the hospital as a random effect was used to estimate the odds ratios (ORs) of abnormal cord insertion. RESULTS: Among the 83 708 women (mean age at delivery = 33.7 years), the frequency of abnormal cord insertion was 4.5%, the median concentration [interquartile range (IQR)] of total PM2.5 was 16.1 (3.61) µg/m3 and the OR per IQR for total PM2.5 was 1.14 (95% confidence interval = 1.06-1.23). In the total PM2.5-adjusted models, total carbon, organic carbon, nitrate, ammonium and chloride were positively associated with abnormal insertion. Organic carbon was consistently, and nitrate tended to be, associated with specific types of abnormal insertion (marginal or velamentous cord insertion). CONCLUSIONS: Exposure to total PM2.5 and some of its components over the first trimester increased the likelihood of abnormal cord insertion.

Trimester-Specific Association of Maternal Exposure to Fine Particulate Matter and its Components With Birth and Placental Weight in Japan.

OBJECTIVE: We investigated which trimester of exposure to PM2.5 and its components was associated with birth and placental weight, and the fetoplacental weight ratio. METHODS: The study included 63,990 women who delivered singleton term births within 23 Tokyo wards between 2013 and 2015. Each day, we collected fine particles on a filter, and analyzed their chemical constituents, including carbons and ions. Trimester-specific exposure to each pollutant was estimated based on the average daily concentrations. RESULTS: Over the third trimester, sulfate exposure tended to be inversely associated with birth weight, and decreased placental weight (difference for highest vs lowest quintile groups = -6.7 g, 95% confidence interval = -12.5 to -0.9). For fetoplacental weight ratio, there was no relationship. CONCLUSIONS: Sulfate exposure over the third trimester may reduce birth weight, particularly placental weight.

Source contributions to multiple toxic potentials of atmospheric organic aerosols.

Fine particulate matter (PM2.5) in the atmosphere is of high priority for air quality management efforts to address adverse health effects in human. We believe that emission control policies, which are traditionally guided by source contributions to PM mass, should also consider source contributions to PM health effects or toxicity. In this study, we estimated source contributions to the toxic potentials of organic aerosols (OA) as measured by a series of chemical and in-vitro biological assays and chemical mass balance model. We selected secondary organic aerosols (SOA), vehicles, biomass open burning, and cooking as possible important OA sources. Fine particulate matter samples from these sources and parallel atmospheric samples from diverse locations and seasons in East Asia were collected for the study. The source and atmospheric samples were analyzed for chemical compositions and toxic potentials, i.e. oxidative potential, inflammatory potential, aryl hydrocarbon receptor (AhR) agonist activity, and DNA-damage, were measured. The toxic potentials per organic carbon (OC) differed greatly among source and ambient particulate samples. The source contributions to oxidative and inflammatory potentials were dominated by naphthalene-derived SOA (NapSOA), followed by open burning and vehicle exhaust. The AhR activity was dominated by open burning, followed by vehicle exhaust and NapSOA. The DNA damage was dominated by vehicle exhaust, followed by open burning. Cooking and biogenic SOA had smaller contributions to all the toxic potentials. Regarding atmospheric OA, urban and roadside samples showed stronger toxic potentials per OC. The toxic potentials of remote samples in summer were consistently very weak, suggesting that atmospheric aging over a long time decreased the toxicity. The toxic potentials of the samples from the forest and the experimentally generated biogenic SOA were low, suggesting that toxicity of biogenic primary and secondary particles is relatively low.

Effects of exposure to chemical components of fine particulate matter on mortality in Tokyo: A case-crossover study.

Fine particulate matter (PM2.5) is composed of a variety of chemical components, and the dependency of the health effects of total PM2.5 on specific components is still under discussion. We hypothesised that specific PM2.5 components are responsible for the health effects, and investigated the association between PM2.5 components and mortality in 23 Tokyo wards. We obtained mortality data from the Ministry of Health, Labour and Welfare for the period from April 2013 to March 2017. At a monitoring site within the study area, we collected daily samples of PM2.5 on a filter, and determined the daily mean concentrations of total carbon (organic carbon and elemental carbon) and ions such as nitrate and sulphate. A case-crossover design was employed, and a conditional logistic regression model was used to estimate the strength of the association. Over the study period, we identified 280,460 total non-accidental deaths, and the average daily mean concentration of total PM2.5 was 16.0 (standard deviation = 8.9) µg/m3. We observed a positive association of total PM2.5 with total, cardiovascular, and respiratory mortality. After adjustment for total PM2.5 and its components associated with mortality in the single-component models, the percentage increase per interquartile range (2.3 µg/m3) increase in the average total carbon concentration of the case- and previous-day was 2.1% (95% confidence interval = 1.0 to 3.1%) for total mortality. Carbon elements were associated with respiratory but not cardiovascular mortality. Our results suggest that specific components of PM2.5 account for its adverse health effects.

Comparative Analysis of PM2.5-Bound Polycyclic Aromatic Hydrocarbons (PAHs), Nitro-PAHs (NPAHs), and Water-Soluble Inorganic Ions (WSIIs) at Two Background Sites in Japan.

Daily PM2.5 (particulate matter with aerodynamic diameter ≤2.5 µm) samples were simultaneously collected at two background sites (Wajima Air Monitoring Station (WAMS) and Fukue-Jima Atmosphere and Aerosol Monitoring Station (FAMS)) in Japan in the East Asian winter and summer monsoon periods of 2017 and 2019, to compare the characteristics of air pollutants among different regions and to determine the possible variation during the long-range transport process. Polycyclic aromatic hydrocarbons (PAHs), nitro-PAHs (NPAHs), and water-soluble inorganic ions (WSIIs) were analyzed. Despite the PM2.5 concentrations at FAMS (8.90-78.5 µg/m3) being higher than those at WAMS (2.33-21.2 µg/m3) in the winter monsoon period, the average concentrations of ∑PAHs, ∑NPAHs, and ∑WSIIs were similar between the two sites. Diagnostic ratios indicated PAHs mainly originated from traffic emissions and mostly aged, whereas NPAHs were mostly secondarily formed during long-range transport. WSIIs at WAMS were mainly formed via the combustion process and secondary reactions, whereas those at FAMS mainly originated from sea salt and dust. Backward trajectories revealed the air masses could not only come from Asian continental coastal regions but also distant landlocked areas in the winter monsoon period, whereas most came from the ocean in the summer monsoon period. These findings can provide basic data for the establishment of prediction models of transboundary air pollutants in East Asia.

Total hydroxyl radical reactivity measurements in a suburban area during AQUAS-Tsukuba campaign in 2017.

Missing hydroxyl radical (OH) reactivity from unknown/unmeasured trace species empirically accounts for 10%-30% of total OH reactivity and may cause significant uncertainty regarding estimation of photochemical ozone production. Thus, it is essential to unveil the missing OH reactivity for developing an effective ozone mitigation strategy. In this study, we conducted simultaneous observations of total OH reactivity and 54 reactive trace species in a suburban area as part of the Air QUAlity Study (AQUAS)-Tsukuba campaign for the summer of 2017 to gain in-depth insight into total OH reactivity in an area that experienced relatively high contributions of secondary pollutants. The campaign identified on average 35.3% of missing OH reactivity among total OH reactivity (12.9 s-1). In general, ozone-production potential estimation categorized ozone formation in this area as volatile organic compound (VOC)-limited conditions, and missing OH reactivity may increase ozone production potential 40% on average if considered. Our results suggest the importance of photochemical processes of both AVOCs and BVOCs for the production of missing OH reactivity and that we may underestimate the importance of reducing precursors in approach to suppressing ozone production if we ignore the contribution of their photochemical products.

Short-term effects of air pollution on daily single- and co-morbidity cardiorespiratory outpatient visits.

Several studies have noted that the existence of comorbidities lead to an increase in the risk of premature mortality and morbidity. Most of the studies examining the effects of air pollution on comorbidity visits were from Northern American countries, with scarce literature from Asia. This study contributes to existing, yet limited understanding of air pollution-comorbidity by examining the effects of daily air pollutants on outpatient single morbidity and comorbid cardiorespiratory visits in Japan. A total of 1,452,505 outpatient cardiorespiratory visits were recorded among the 21 Japanese cities from 2013 to 2016. Daily outpatient cardiorespiratory visit data were obtained from a health insurance claims database managed by the Japan Medical Data Center Co., Ltd. (JMDC). A time-stratified case crossover analysis coupled with Generalized Additive Mixed Model was used to analyze the association of daily air pollutants (particulate matter 2.5 µm or less in diameter, ozone and nitrogen dioxide) on daily single (respiratory and cardiovascular) and comorbidity health outcomes. We further examined single and cumulative effects for 0-3 and 0-14 lag periods. Ozone, NO2, and PM2.5 were positively associated with cardiorespiratory visits in either shorter or longer lags, with more apparent comorbidity associations with NO2 exposure. A 10-unit increase in NO2, after adjusting for ozone, was associated with a 2.24% (95% CI: 1.34-3.15) and 6.49% (95% CI: 5.00-8.01) increase in comorbidity visit at Lag 0 (of Lag 0-3) and cumulative lag 0-3, respectively. Our results contribute to existing evidence suggesting that short-term and extended exposure to air pollution elicit health risks on cardiovascular, respiratory and comorbid clinic visits. Exposure to NO2, in particular, was associated with increase in the risk of single and comorbidity cardiorespiratory visits. Results can be potentially utilized for both individual health (e.g. risk population health management) and health facility management (e.g. health visit influx determination).

Association of Fine Particulate Matter Exposure With Bystander-Witnessed Out-of-Hospital Cardiac Arrest of Cardiac Origin in Japan.

Importance: Out-of-hospital cardiac arrests (OHCAs) are a major public health concern and a leading cause of death worldwide. Exposure to ambient air pollution is associated with increases in morbidity and mortality and has been recognized as a leading contributor to global disease burden. Objective: To examine the association between short-term exposure to particulate matter with a diameter of 2.5 µm or smaller (PM2.5) and the incidence of OHCAs of cardiac origin and with the development of initial cardiac arrest rhythm. Design, Setting, and Participants: This case-control study used data from cases registered between January 1, 2005, and December 31, 2016, in the All-Japan Utstein Registry, a prospective, nationwide, population-based database for OHCAs across all 47 Japanese prefectures. These OHCA cases included patients who had bystander-witnessed OHCAs and for whom emergency medical services responders initiated resuscitation before hospital transfer. A case-crossover design was employed for the study analyses. A prefecture-specific, conditional logistic regression model to estimate odds ratios was applied, and a random-effects meta-analysis was used to obtain prefecture-specific pooled estimates. All analyses were performed from May 7, 2019, to January 23, 2020. Main Outcomes and Measures: The main outcome was the association of short-term PM2.5 exposure with the incidence of bystander-witnessed OHCAs of cardiac origin. The differences in the distribution of initial cardiac arrest rhythm in OHCAs among those with exposure to PM2.5 were also examined. Results: In total, 103 189 OHCAs witnessed by bystanders were included in the final analysis. Among the patients who experienced such OHCAs, the mean (SD) age was 75 (15.5) years, and 62 795 (60.9%) were men. Point estimates of the percentage increase for a 10-µg/m3 increase in PM2.5 at lag0-1 (difference in mean PM2.5 concentrations measured on the case day and 1 day before) demonstrated a statistically significantly higher incidence of OHCA across most of the 47 prefectures, without significant heterogeneity (I2 = 20.1%; P = .12). A stratified analysis found an association between PM2.5 exposure and OHCAs (% increase, 1.6; 95% CI, 0.1%-3.1%). An initial shockable rhythm, such as ventricular fibrillation or pulseless ventricular tachycardia (% increase, 0.6; 95% CI, -2.0% to 3.2%), was not associated with PM2.5 exposure. However, an initial nonshockable rhythm, such as pulseless electrical activity and asystole, was associated with PM2.5 exposure (% increase, 1.4; 95% CI, 0.1%-2.7%). Conclusions and Relevance: Findings from this study suggest that increased PM2.5 concentration is associated with bystander-witnessed OHCA of cardiac origin that commonly presents with nonshockable rhythm. The results support measures to reduce PM2.5 exposure to prevent OHCAs of cardiac origin.

Paradigm shift in aerosol chemical composition over regions downwind of China.

A rapid decrease in PM2.5 concentrations in China has been observed in response to the enactment of strong emission control policies. From 2012 to 2017, total emissions of SO2 and NOx from China decreased by approximately 63% and 24%, respectively. Simultaneously, decreases in the PM2.5 concentration in Japan have been observed since 2014, and the proportion of stations that satisfy the PM2.5 environmental standard (daily, 35 µg/m3; annual average, 15 µg/m3) increased from 37.8% in fiscal year (FY) 2014 (April 2014 to March 2015) to 89.9% in FY 2017. However, the quantitative relationship between the PM2.5 improvement in China and the PM2.5 concentration in downwind regions is not well understood. Here, we (1) quantitatively evaluate the impacts of Chinese environmental improvements on downwind areas using source/receptor analysis with a chemical transport model, and (2) show that these rapid emissions reductions improved PM2.5 concentrations both in China and its downwind regions, but the difference between SO2 and NOx reduction rates led to greater production of nitrates (e.g., NH4NO3) due to a chemical imbalance in the ammonia-nitric acid-sulfuric acid-water system. Observations from a clean remote island in western Japan and numerical modeling confirmed this paradigm shift.

Hourly association between ambient PM2.5 and emergency ambulance dispatches in 11 cities in Japan.

Numerous epidemiological studies have demonstrated that short-term exposure to ambient PM2.5 increases mortality and morbidity. Investigating the association using hourly ambient PM2.5 exposure may provide important insights, as current evidence is limited mostly to daily lag term. This study aimed to investigate the hourly association between ambient PM2.5 concentrations and all-cause emergency ambulance dispatches (EAD) in 11 cities in Japan. We used a time-stratified case-crossover design and examined the hourly lags of ambient PM2.5 up to 24 h (unconditional distributed lags and moving average lags) using a conditional Poisson regression model. A significant increase in all-cause EAD was observed at lag 0 h [relative risk (RR): 1.0037 (95% CI: 1.0000, 1.0074)] and all moving average lags. The highest RR was observed within the first 6 h (at lag 0-5 h) [RR: 1.0091 (95% CI: 1.0068, 1.0114)], with a slight ascending pattern. This was followed by a descending pattern at lags 0-11, 0-17, and 0-23 h, but significant positive RR was observed even at lag 0-23 h, when the lowest RR was observed [RR: 1.0072 (95% CI: 1.0044, 1.0100)]. Though similar pattern was observed among the elderly, a different pattern was observed among the children (gradually ascending pattern). We conclude that all-cause EAD could be triggered by ambient PM2.5 exposure with very short lags.