Asian Journal of Atmospheric Environment最新文献

Behind their role as carbon sinks, mangrove soil can also emit greenhouse gases (GHG) through microbial metabolism. GHG flux measurments of mangroves are scarce in many locations, including Indonesia, which has one of the world’s most extensive and carbon-rich mangrove forests. We measured GHG fluxes (CO₂, CH₄, and N₂O) during the wet season in Benoa Bay, Bali, a bay with considerable anthropogenic pressures. The mangroves of this Bay are dominated by Rhizophora and Sonneratia spp and have a characteristic zonation pattern. We used closed chambers to measure GHG at the three mangrove zones within three sites. Emissions ranged from 1563.5 to 2644.7 µmol m⁻² h⁻¹ for CO₂, 10.0 to 34.7 µmol m⁻² h⁻¹ for CH₄, and 0.6 to 1.4 µmol m⁻² h⁻¹ for N₂O. All GHG fluxes were not significantly different across zones. However, most of the GHG fluxes decreased landward to seaward. Higher soil organic carbon was associated with larger CO₂ and CH₄ emissions, while lower redox potential and porewater salinity were associated with larger CH₄ emissions. These data suggest that soil characteristics, which are partially determined by location in the intertidal, significantly influence GHG emissions in soils of these mangroves.

This study aims to understand the impact of previous air quality improvement policies on historical emission changes by examining long-term emission trends in Korea. Annual emissions from 2000 to 2018 were estimated using Korea’s official emissions inventory, the Clean Air Policy Support System (CAPSS). To ensure a consistent comparison, standardization of the method for calculating emissions and unification of the reported emission sectors were conducted each year. Furthermore, Korea’s emissions history was compared with that of neighboring countries, such as China and Japan. The annual emissions of these countries were acquired from the HTAPv3 emissions inventory, an international long-term emission trend study. For comparison, the emission source classification of Korea was matched with that of HTAPv3. As a result of the analysis, NO_x and SO_x emissions in Korea have shown decreasing trends, whereas VOCs (volatile organic compounds) have indicated a gradual increasing trend since 2000. Compared to the previous period of implementing South Korea’s air quality improvement policy, changes in NOx and SOx emissions, which are combustion-related pollutants, showed a relationship with the policy’s timeline. However, non-combustion-related pollutants such as VOCs did not exhibit such a relationship. It was concluded that the related policies were not as effective in reducing VOCs as planned in the policy. By comparing the emission trends of Japan, Korea, and China, it was confirmed that Japan was the first country to experience a decrease in combustion-related pollutants emissions, followed by Korea and China. Additionally, combustion-related pollutants decreased in all three countries, whereas VOCs decreased only in Japan. VOC is a precursor material generating secondary PM_2.5 and Ozone; considering that, if relevant policies are additionally implemented to control future PM_2.5 concentrations, and to reduce emissions efficiently and effectively, Japan’s VOC reduction policies can be applied to Korea’s emission reduction policies. These results are expected to serve as important references when establishing future air quality improvement policies in Korea.

In Japan, the number of elderly people in need of nursing care is increasing while the population of young people is decreasing, and the potential for labor shortages in the field of elder care is of great concern. This study aimed to estimate the behavior of the elderly by using sensors to monitor indoor air quality (IAQ), without placing undue burden on the elderly or their caregivers. Odor and carbon dioxide (CO₂) concentrations were monitored in a private room of a nursing home in the Kanto Region of Japan, the behaviors of the resident and staff members were recorded, and the relationship between the two was analyzed. Both odor and CO₂ concentrations were higher when the resident was present than when absent, indicating that the resident was one of the main sources of indoor odor and CO₂. In addition, after the resident entered the room, the CO₂ concentration increased and remained stable, whereas the odor concentration tended to vary after the resident entered the room, first increasing and later decreasing. This suggested that the increase or decrease in odor could be used to monitor the behavior of the resident and staff members. The relationship between the slopes of odor and CO₂ in typical behavioral events suggest that if only odor increases and CO₂ does not change, the likelihood of the event in which feces were observed during diaper changes is high. In addition, based on the behavior near the sensor, the rate of CO₂ and odor emissions differed between the elderly resident and the younger staff members, suggesting that the ratio of odor slope to CO₂ slope may be greater in the elderly than in younger people. Furthermore, the repeated number of increases and decreases in odor and CO₂ suggested that multiple events could be distinguished. These results suggest that IAQ can be utilized to estimate the behavior of residents and staff in nursing care facilities for the elderly.

Biogenic volatile organic compounds (BVOCs) with high photochemical activity and short atmospheric lifetimes are major contributors to tropospheric ozone and other photochemical air pollution. Although several studies have been conducted on BVOC emissions in Japan, no comprehensive observations have been made to determine the actual state of BVOCs in the atmosphere. Therefore, we conducted time-resolved measurements of atmospheric BVOCs in urban and forested areas throughout the year. The concentrations of BVOCs were higher in summer than in the other seasons. Isoprene concentrations were higher during hours with higher temperatures and solar radiation. However, there were also months and times of the year when monoterpenes showed high concentrations, which indicates that the behavior of the BVOC components differed depending on the time of the year. The results of the propylene equivalent concentration indicated that BVOCs considerably contributed to tropospheric ozone production. The year-long observations of BVOCs in this study contribute to our understanding of the actual status of atmospheric BVOC concentrations and components and the uncertainty in the calculation results of chemical transport models.

High-level ozone (O₃) events observed around major urban regions in the middle latitudes are correlated with high temperatures (T-O₃ correlation). Therefore, the effects of global warming on the future O₃ levels are a matter of concern. The T-O₃ correlation is caused by various physicochemical and meteorological processes, the importance of which can differ by region. This statistical analysis focused on the correlation in the extremely high ranges, because the lower ranges would only act as noise in elucidating the conditions at which high temperatures and high levels of O₃ occur. This methodology was applied to the greater Tokyo region after 2001, where severe O₃ events frequently occurred when the sea breeze system developed in summer. To select sample days for the analysis, this study set up twofold filtering: (1) a large threshold for midday sunshine duration and (2) a typical variation pattern to roughly judge sea breeze days, mostly essential weather pattern for high-level O₃ events in the region. The most notable result was a decrease in O₃ corresponding to the reduction in non-methane hydrocarbons (NMHC) from Period I (2001–2007) to Period III (2017–2019). As the NMHC rank reduced, the linear regression line for the T-O₃ correlation shifted downward, but its slope (ppb/°C) remained around 10, except that temporary spikes in O₃ levels and temperatures occurred at moderate NMHC levels. From an urban meteorological perspective, the wind speed in the mature stage of the sea breeze is the major factor behind the T-O₃ correlation.

To examine the heterogeneous photonitration of pyrene with NO₂ (approximately 0.2 ppm) on a heavy-traffic road, we studied the photonitration of pyrene adsorbed (pyrene_ads) on silica gel, which was used as SiO₂ in particulate matter (PM), with NO₂ (10.2, 2.0, and 0.20 ppm) under the atmospheric concentration ratio of pyrene_ads to NO₂ and compared the results with those obtained in the dark. The effects of irradiation, wavelength, and oxygen concentration in a NO₂ diluent on the photonitration were examined using a fluidized-bed column irradiated with simulated or real sunlight. Under the UV-light absorption of pyrene, the concentration of pyrene decreased exponentially in accordance with a pseudo-first-order reaction, while in the dark, it decreased sigmoidally in accordance with a H⁺-autocatalyzed reaction. The distribution and the yields of formed nitration products and their photooxidation products were affected by the light intensity, concentrations of NO₂, and oxygen in the NO₂ diluent. In the photonitration experiments using a high-pressure mercury lamp, formed 1-nitropyrene and minor dinitropyrenes were decreased by the transformation into their photooxidation products. Under 8-h exposure of pyrene to 10.2-ppm NO₂, the yield of 1-nitropyrene was 42% in N₂ and 28% in air. The oxygen inhibitory effect can be explained by the energy transfer from ¹pyrene* to oxygen. Radical cation intermediate (pyrene^•+-NO₂⁻) was proposed for 1-nitropyrene formation. Under 24-h exposure of pyrene to 2.0-ppm NO₂, the yields of 1-nitropyrene and the photooxidation products were 21.6% and 8.0%, respectively, in N₂ and 4.9% and 3.8%, respectively, in air. Under 24-h exposure of pyrene to 0.20-ppm NO₂, which is two times the 1-h NO₂ standard in the USA and China, the yields of 1-nitropyrene and the photooxidation products were 2.3% and 3.4%, respectively, in N₂ and 2.1% and 0.9%, respectively, in air. The significant decrease in the yields of 1-nitropyrene and the photooxidation products under the concentration of 0.20-ppm NO₂ can be explained by their easy photodecomposition with the increase in the photolysis of pyrene. Under the concentration of 0.20-ppm NO₂ in air, which is approximately the concentration on heavy-traffic roads, the decay rate of pyrene by the photonitration was increased by own photolysis, although the photonitration was inhibited by oxygen in air.

Exposure to benzene and other volatile organic compounds (VOCs) like toluene, ethylbenzene, o-, m-, and p-xylene (BTEX) at a fuel station is hazardous for the workers. This study aims to estimate the health risk for worker due to the exposure of BTEX after implementation of vapour recovery system (VRS) at fuel stations. Air samples were collected using low-flow sampling pump as per NIOSH method by using Tenax (sorbent) tubes and charcoal (sorbent) tubes. Target compounds were extracted using acetone and analysed by gas chromatography equipped with flame ionization detector (FID). The cancer risk (CR) and hazard quotient (HQ) were estimated to assess the cancer and non-cancer risk following the United States of Environmental Protection Agency (USEPA) updated methodology. The average concentration of VOCs at the fuel station is found in the order toluene > benzene > xylene > ethylbenzene which may be attributed to the composition of fuel (petrol/diesel). Benzene is the most carcinogenic among BTEX, which is found to be 217 ± 9 µg m⁻³ and 158 ± 9 µg m⁻³ in the month of November 2021 using Tenax sorbent and charcoal sorbent tubes, respectively. The high concentration observed using Tenax sorbent may be attributed to its high adsorption efficacy than charcoal due to larger surface area and porosity. The 7-month average CR value of benzene was 9 × 10⁻⁴ using Tenax sorbent and exceeds the acceptable range of 1 × 10⁻⁶. CR of benzene exposure at the fuel station under study is also compared with that of outdoor ambient air exposure. Benzene measurement data for the same duration was taken from nearby online monitoring station of Delhi Pollution Control Committee (DPCC) PUSA to estimate CR value for outdoor ambient air benzene exposure. The value of HQ for benzene was observed > 1 which exceeds the acceptable value and hence increased the non-cancer health risk also. Hazard index (HI) value for BTEX is also greater than 1 which indicates adverse health effects of benzene and other VOCs at the fuel station. The high CR and HQ values for benzene are a matter of concern for fuel station workers.

This study aimed to identify the factors causing NH₃ emissions in the South Korean Peninsula and West Sea region. To analyze the trends of NH₃ and other air pollutants, such as NO_x, CO, and NR-PM₁, we collected samples from six supersites across the peninsula, a roadside in Seoul, and the West Sea over different sampling periods, ranging from 1 month to 1 year. The highest NH₃ concentrations were found at rural areas, ascribed to agricultural activities, particularly NH₄NO₃ decomposition at high summer temperatures. Areas with low population densities recorded the lowest NH₃ concentrations, attributed to the lack of anthropogenic activities. A roadside field experiment confirmed the close link between ambient NH₃ and vehicle emissions in urban regions by showing a strong correlation between CO and NO_x concentrations and that of NH₃. Moreover, we examined oceanic emissions near the eastern coast of South Korea in the West Sea. Long-range transportation studies confirmed that most of the pollutants (NH₃, CO, and PM₁) were transported by wind from the northeastern region of China. A maritime origin study showed that oceanic emissions and NH₄NO₃ decomposition in the atmosphere owing to high temperatures were the causing NH₃ pollution. These findings provided valuable insights into the emission sources of NH₃ in primary air pollutants in South Korea, highlighting the contributions of land-based and oceanic sources. Our study can help inform policymakers and stakeholders for developing effective regional air pollution control strategies.

Records of stable isotopes (²H and ¹⁸O), deuterium excess (d-excess) and tritium (³H) values in precipitation (P) during 1990–2022, together with long-term time series (1919–2022) of air temperature (T) and P-amount values at the Damascus station, were analysed to explore the seasonal and annual variability patterns of those parameters in P and assess the vulnerability to climate change in this area. Variation of the annual average air T values over the period 1919–1969 shows an increase gradient of ≈ + 0.1 °C/decade. However, a remarkable much higher gradient (+ 0.64 °C/decade) is calculated for the period 1990–2022. The average P-amount value calculated for the last three decades (≈185 mm) was lower by ≈28 mm, compared to the value (≈213 mm), relative to the reference period (1919–1969). This significant decline in the annual P-amount value by ≈11–13%, accompanied by an annual heating of 0.2–0.6 °C/decade in the annual air T, is likely the result of the climate change affecting this area. The linear relationships between annual average δ¹⁸O and annual average δ²H values versus time over the period 1990–2019 indicate increased gradients in both stable isotopes (≈0.3–0.5‰ and ≈1.1–3.2‰ per decade for δ¹⁸O and δ²H, respectively), accompanied with a decrease gradient of ≈0.9–1.1‰ per decade in d-excess values. Variability of annual ³H concentrations towards low levels (< 6 TU) during the later years strongly suggests the return back towards the cosmogenic production of this radioisotope in the upper atmosphere. Information gained from this work would offer new insights to improve the understanding of the temporal variability of P isotopes and assess the risks associated with climate change on the natural water resources in the Eastern Mediterranean region.

The adverse effect of air pollution has always been a problem for human health. The presence of a high level of air pollutants can cause severe illnesses such as emphysema, chronic obstructive pulmonary disease (COPD), or asthma. Air quality prediction helps us to undertake practical action plans for controlling air pollution. The Air Quality Index (AQI) reflects the degree of concentration of pollutants in a locality. The average AQI was calculated for the various cities in China to understand the annual trends. Furthermore, the air quality index has been predicted for ten major cities across China using five different deep learning techniques, namely, Recurrent Neural Network (RNN), Bidirectional Gated Recurrent unit (Bi-GRU), Bidirectional Long Short-Term Memory (BiLSTM), Convolutional Neural Network BiLSTM (CNN-BiLSTM), and Convolutional BiLSTM (Conv1D-BiLSTM). The performance of these models has been compared with a machine learning model, eXtreme Gradient Boosting (XGBoost) to discover the most efficient deep learning model. The results suggest that the machine learning model, XGBoost, outperforms the deep learning models. While Conv1D-BiLSTM and CNN-BiLSTM perform well among the deep learning models in the estimation of the air quality index (AQI), RNN and Bi-GRU are the least performing ones. Thus, both XGBoost and neural network models are capable of capturing the non-linearity present in the dataset with reliable accuracy.