Impacts on air dose rates after the Fukushima accident over the North Pacific from 19 March 2011 to 2 September 2015

A fleet of thirteen in-service global container ships continuously measured the air dose rates over the North Pacific after the Fukushima Daiichi Nuclear Power Station (FDNPS) accident. The results showed that the elevated air dose rates over the Port of Tokyo and the FDNPS emissions are significantly correlated (log(emission fluxes) = 54.98 x (air dose rates) (R = 0.95, P-value<0.01), and they are also significantly correlated with the Tsukuba deposition fluxes (log(deposition fluxes) = 0.47 + 30.98 (air dose rates) (R = 0.91, P-value<0.01). These results demonstrate the direct impact of the FDNPS emissions on the depositions of radionuclides and the air dose rates over the Port of Tokyo. Over the North Pacific, the correlation equations are log(emission fluxes) = -2.72 + 202.36 x (air dose rates over the northwestern Pacific) (R = 0.40, P-value<0.01), and log(emission fluxes) = -0.55 + 80.19 x (air dose rates over the northeastern Pacific) (R = 0.29, P-value = 0.0424). These results indicate that the resuspension of the deposited radionuclides have become a dominant source in the transport of radionuclides across the North Pacific. Model simulations show underestimated air dose rates during the periods of 22-25 March 2011 and 27-30 March 2011 indicating the lack of mechanisms, such as the resuspension of radionuclides, in the model

Fine Ash-Bearing Particles as a Major Aerosol Component in Biomass Burning Smoke

Biomass burning (BB) events are occurring globally with increasing frequency, and their emissions are having more impacts on human health and climate. Large ash particles are recognized as a BB product with major influences on soil and water environments. However, fine-ash particles, which have diameters smaller than several microns and characteristic morphologies and compositions (mainly Ca and Mg carbonates), have not yet been explicitly considered as a major BB aerosol component either in field observations or climate models. This study measured BB aerosol samples using transmission electron microscopy (TEM) and ion chromatography during the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) campaign. We show that significant amounts of fine ash-bearing particles are transported \u3e100 km from their fire sources. Our environmental chamber experiments suggest that they can act as cloud condensation and ice nuclei. We also found considerable amounts of fine ash-bearing particles in the TEM samples collected during previous campaigns (Biomass Burning Observation Project and Megacity Initiative: Local and Global Research Observations). These ash particles are commonly mixed with organic matter and make up ∼8% and 5% of BB smoke by number and mass, respectively, in samples collected during the FIREX-AQ campaign. The measured ash-mass concentrations are approximately five times and six times greater than those of BB black carbon and potassium, respectively, scaling to an estimated global emission of 11.6 Tg yr−1 with a range of 8.8–16.3 Tg yr−1. Better characterization and constraints on these fine ash-bearing particles will improve BB aerosol measurements and strengthen assessments of BB impacts on human health and climate

Effects of Mountains on Aerosols Determined by AERONET/DRAGON/J-ALPS Measurements and Regional Model Simulations

The NASA/AErosol RObotic NETwork field campaign Distributed Regional Aerosol Gridded Observation Networks/Joint work to the AerosoL Properties and Process Simulations was conducted from March 2020 to May 2021 in Nagano, Japan. Twelve sun photometers were installed around Nagano prefecture. The effects of topography on aerosols were studied using observations and simulations. In this study, a regional chemical transport model (SCALE-Chem) was employed. Three numerical experiments were conducted: E1 (control experiment), E2 (E1 without topography), and E3 (E1 with removal of all anthropogenic emissions over Nagano prefecture). In E2, the terrain effect was not considered; the difference between E1 and E2 indicated the influence of mountains. The differences between E1 and E3 evaluate the local emission effect. In some cases, the mountainous terrain seemed to have suppressed aerosol inflow (i.e., reduced aerosol concentration), while in other cases, the mountains contributed to aerosol retention on days when aerosols tended to accumulate in mountain basins due to local emissions. Thus, while mountains prevent the inflow of aerosols from outside, they also contribute to increased aerosol concentration in the basin. Naturally, more significant effects are produced by meteorological conditions and the presence or absence of transboundary pollution from the outside. From observations and model simulations, we found that the aerosol concentration was not high around the J-ALPS site because of the mountain effect that prevents advection from the outside, even when transboundary pollution was observed in Japan in March 2020

Ensemble Dispersion Simulation of a Point-Source Radioactive Aerosol Using Perturbed Meteorological Fields over Eastern Japan

We conducted single-model initial-perturbed ensemble simulations to quantify uncertainty in aerosol dispersion modeling, focusing on a point-source radioactive aerosol emitted from the Fukushima Daiichi Nuclear Power Plant (FDNPP) in March 2011. The ensembles of the meteorological variables were prepared using a data assimilation system that consisted of a non-hydrostatic weather-forecast model with a 3-km horizontal resolution and a four-dimensional local ensemble transform Kalman filter (4D-LETKF) with 20 ensemble members. The emission of radioactive aerosol was not perturbed. The weather and aerosol simulations were validated with in-situ measurements at Hitachi and Tokai, respectively, approximately 100 km south of the FDNPP. The ensemble simulations provided probabilistic information and multiple case scenarios for the radioactive aerosol plumes. Some of the ensemble members successfully reproduced the arrival time and intensity of the radioactive aerosol plumes, even when the deterministic simulation failed to reproduce them. We found that a small ensemble spread of wind speed produced large uncertainties in aerosol concentrations

A numerical study of lightning-induced NOx and formation of NOy observed at the summit of Mt. Fuji using an explicit bulk lightning and photochemistry model

This study coupled a meteorological model with explicit bulk lightning and chemical transport models to investigate the impacts of lightning-induced nitrogen oxides (LNOx) on nitrogen monoxide (NO), nitrogen dioxide (NO2), and total reactive nitrogen oxide (NOy) measured on August 22, 2017, at the top of Mt. Fuji, Japan. Our simulation results indicated that the LNOx emitted around Wakasa Bay in the windward area of Mt. Fuji largely contributed to the NOy content measured at the top of Mt. Fuji. Furthermore, sensitivity experiments regarding the height of LNOx emissions indicated that the NOy content measured atop Mt. Fuji originated from LNOx emitted below 6 km. Our simulation assumed that a two-mode vertical distribution of LNOx emissions was more consistent with measured NOy at Mt. Fuji than a single-mode structure assumption in this case. A comparison of simulated NOx (= NO + NO2) and measured NOx at Mt. Fuji indicated that the reaction rates of the NO and NO2 cycles were well reproduced in our model; however, the ratio of NOz (NOy species other than NOx) to NOy estimated by the model were lower than the observed value, implying that the model either underestimated the reaction rate of LNOx or overestimated the wet removal of lightning-induced NOz. Finally, our results also suggest that the simultaneous observation of NOy and NOx is important for understanding LNOx emissions, subsequent atmospheric chemical reactions, and removal processes, as well as validating chemical transport models

アジア域における間接的酸性化効果 : 硫酸によりエアロゾル相から追い出された硝酸ガスによる沈着の促進

東アジア酸性雨モニタリングネットワーク(EANET)の国内6地点の観測結果から，間接的酸性化効果が越境大気汚染に伴い生じている事が分かった。SO42-濃度増加に伴いエアロゾル中のNO3- が追い出され，HNO3ガス濃度が増加する。 HNO3ガスの沈着速度は非常に速いので，結果としてトータル(ガス状＋エアロゾル状)のNO3-濃度が変化しなくても，NO3-の沈着量が増加する事になる。西日本の日本海側では，アジア大陸からのアウトフローの影響下で間接的酸性化効果は顕著になり，一方，海塩粒子が豊富にある冬季日本海側ではこの効果はあまり見えなかった。Indirect acidification, i.e., enhancement of semi-volatile aerosol components deposition associated with increased SO42- concentration has now been shown to occur in general air pollution, analyzing Acid Deposition Monitoring Network in East Asia (EANET) monitoring data collected at six stations in Japan. This effect was firstly detected as a result of volcanic SO2 plumes (Satsumabayashi et al., 2004, Kajino et al., 2005). Results indicate that as SO42- concentration increases, NO3- in aerosol phase is expelled, increasing the HNO3 gas concentration. The deposition of HNO3 gas occurs at a high velocity, consequently accelerating the deposition of NO3- despite a constant total (gas plus aerosol) nitrate concentration. In western Japan, this indirect acidification is most influential from spring to autumn, when the Asian continental outflow carries sulfate-rich contaminated air masses, but is not pronounced in the air masses containing abundant sea-salt particles and related cation components in aerosols.東アジア酸性雨モニタリングネットワーク(EANET)の国内6地点の観測結果から，間接的酸性化効果が越境大気汚染に伴い生じている事が分かった。SO42-濃度増加に伴いエアロゾル中のNO3- が追い出され，HNO3ガス濃度が増加する。 HNO3ガスの沈着速度は非常に速いので，結果としてトータル(ガス状＋エアロゾル状)のNO3-濃度が変化しなくても，NO3-の沈着量が増加する事になる。西日本の日本海側では，アジア大陸からのアウトフローの影響下で間接的酸性化効果は顕著になり，一方，海塩粒子が豊富にある冬季日本海側ではこの効果はあまり見えなかった。Indirect acidification, i.e., enhancement of semi-volatile aerosol components deposition associated with increased SO42- concentration has now been shown to occur in general air pollution, analyzing Acid Deposition Monitoring Network in East Asia (EANET) monitoring data collected at six stations in Japan. This effect was firstly detected as a result of volcanic SO2 plumes (Satsumabayashi et al., 2004, Kajino et al., 2005). Results indicate that as SO42- concentration increases, NO3- in aerosol phase is expelled, increasing the HNO3 gas concentration. The deposition of HNO3 gas occurs at a high velocity, consequently accelerating the deposition of NO3- despite a constant total (gas plus aerosol) nitrate concentration. In western Japan, this indirect acidification is most influential from spring to autumn, when the Asian continental outflow carries sulfate-rich contaminated air masses, but is not pronounced in the air masses containing abundant sea-salt particles and related cation components in aerosols