Hi! I am Arthur, currently a PhD student in Imasu Lab affliated with AORI, UTokyo. I obtained my bachelor's degree in Earth System Science at the Chinese University of Hong Kong (2016-2021), and am a recipient of Lotte Foundation Scholarship.
Remote sensing | Air pollution | Climate change
An INFJ, science student and HKer who pursues a stoic way of life. Aiming to a research career, I believe that new knowledge and immediate action are keys to a better world. I speak Japanese, English, Madarin, and Cantonese :)
Python
Shell
Fortran
R
HTML5/CSS3
Google Earth Engine
ArcGIS Pro/QGIS
MPhil in Natural Environmental Studies (2022/4 - 2024/3)
Atmosphere and Ocean Research Institute, University of Tokyo
Thesis: Tropospheric ozone retrieval using thermal-IR band of TANSO-FTS-2 on GOSAT-2: An analysis over metropolitan area in Japan
B.Sc.(Hons) in Earth System Science (2016/9 - 2021/8)
Earth System Science Programme, Chinese University of Hong Kong
Thesis: Development of aviation emission model in Hong Kong
Exchange Program in Keio University (2019/9 - 2020/8)
International Center, Keio University
Temperature anomoly, CO2 and CH4 emissions, Short-lived climate pollutants (SLCPs) etc.
Source/sink of air pollutants, long-range transport, meteorological effects etc.
GOSAT and GOSAT-2 retrieval, intercomparison of atmospheric soundings etc.
The Greenhouse gases Observing SATellite-2 (GOSAT-2, launched on October 29, 2018) has shown immense
potential in CO2 and CH4 research, as a successor of GOSAT; however, the retrieval of tropospheric
ozone is yet to be analyzed. Meanwhile, metropolitan areas are regarded as tropospheric ozone source
for emission of ozone precursors (NOx and VOC) by anthropogenic activities. The extreme surface
temperature due to urban heat island effect can potentially modify the averaging kernel (AK) of
satellite retrieval; this effect, "thermal contrast (TC)", is expected to favor the analysis of
ozone in
urban areas. In this study, we present the first result of GOSAT-2 ozone retrieval, while
investigating the
impact of TC on the performance of retrieval.
"Seeing the unseen: climate change from space"
by Arthur (an introductory material of spaceborn observation, 2023/10)
"Review of tropospheric
ozone observation from space (infrared sounding)" by Arthur (lab seminar, 2022/10)
The tropospheric ozone retrieval is performed using thermal infrared
(TIR) band from the nadir-looking instrument Thermal And Near infrared Sensor for carbon Observation
– Fourier Transform Spectrometer-2 (TANSO-FTS-2), which is onboard GOSAT-2. For retrieval in
megacities,
the targeting mode of FTS-2 with around 40×40 km2 domain is utilized. In
the retrieval process, we basically apply the optimal estimation and the Line-By-Line Radiative
Transfer Model (LBLRTM) as the forward model, with the spectroscopic line parameters from HITRAN
2016 database. The climatological mean of the tropospheric ozone in Tokyo is applied as the a priori
profile, while the Japanese reanalysis data JRA-55 is applied as a priori of atmospheric conditions.
Meanwhile, sequantial retrieval approach is applied to reduce error in ozone retrieval, where
temperature and water vapour are being retrieved prior to ozone.
For validation, we use ozonesonde data provided by WOUDC with >130 sites worldwise with
averaging kernel smoothing method. The performance of
retrieval is evaluated by the degree of freedom of signal (DOFS), root-mean square error (RMSE) and
mean bias (BIAS), in comparison with previous satellite missions such as TES and IASI.
"Research plan for the retrieval
of tropospheric ozone on urban area (Tokyo)"
by Arthur (course seminar, 2023/1)
Li, A. H. W. & Imasu, R. (2023). Retrieval of ozone profile using thermal-IR band of TANSO-FTS-2 on GOSAT-2: An analysis over metropolitan area in Japan. American Geophysical Union Meeting 2023, Online.
Li, A. H. W. & Imasu, R. (2023). Seeing the unseen: Climate change from space. The NENV Symposium 2023, University of Tokyo, Chiba, Japan.
Li, A. H. W. & Imasu, R. (2023). Retrieval of short-lived climate pollutant (SLCP) using TANSO-FTS-2 on GOSAT2: a case study of tropospheric ozone. The 2023 University Allied Workshop on Changing Climate, Chiba, Japan.
Li, A. H. W., Imasu, R. & Saitoh, N. (2023). Retrieval of tropospheric ozone using TANSO-FTS-2 on GOSAT-2: a global analysis and validation. Japan Geoscience Union Meeting 2023, Chiba, Japan.
The aviation industry emits both air pollutants and greenhouse gases, which affects local air
quality and climate. With the increasing air transportation in the future, the amount of
emissions by aircraft is expected to increase.
Furthermore, the aircraft emission is considered a major source of NOx and water vapour in high
altitude,
affecting atmospheric chemistry. However, the aircraft emissions are commonly underestimated and
remained a research gap.
Therefore, this study aims at better estimation of aviation emission through statistical
modelling approach.
This study applies new generation aviation tracking system, ADS-B, as input data to investigate the spatial distribution of aircraft emissions. In the first stage, data collected by Flightradar24 was used; in second stage, we configured our own ADS-B receiver using Raspberry Pi to collect data near Hong Kong International Airport (HKIA). For calculating the emissions below 3,000 ft, we utilized ICAO Engine Exhaust Emissions Databank to estimate fuel burn and corresponding emissions. The information of aircraft engines are default engine setting according to manufacturer. To validate the result, we selected 25th April 2021 and compared the EUROCONTROL Advanced Emission Model (AEM) and the emission inventory by Hong Kong Environmental Protection Department (HKEPD) with our estimation. Also, we proposed a new definition of TIM of the aircraft using horizontal and vertical speed of the aircraft, calculated from the ADS-B data.
We found that the AEM model underestimated aircraft emission in Hong Kong International Airport on the selected date, due to inaccurate repersentation of time-in-mode (TIM) of the aircraft. Specifically, the ICAO denifition of aircraft phrases underestimated the total time spent of aircraft in HKIA by 34%. The underestimation contributed to discrepancy of all emissions of air pollutants, where carbon monoxide (CO) was only 55% of our estimation and nitrogen oxides (NOx) was 87%. We found that aircraft emission (below 3,000 ft) accumulates in the parking lot of the airport due to suspended waiting time of aircrafts. Meanwhile, the high thrust during take-off also produces second largest amount of air pollutants. Our new definition of TIM reduced the discrepancy of NOx emission by 10% comparing to EPD results.
Since the end of 2019, COVID-19 was widespread among cities including Hong Kong. The impact of the pandemic not only shaped people’s life, but also affected the direct and indirect emission of air pollutants from human activity. The reduction of vehicle and industrial activity is expected to reduce the concentrations of pollutants, but the magnitude has not been quantified yet. Therefore, we aim to quantify the impact of COVID-19 on HK air pollution, and identify the regions with highest impact.
The study period was set from November 2019 to May 2020 according to the timeline of COVID-19 in Hong Kong, and compared to same period in 2018-19 and 2017-18. The air pollution data (2001 to 2020) were collected from Hong Kong Environmental Protection Department (HKEPD), including both general monitoring stations (in residential areas) and roadside monitoring stations. Meanwhile, VOC data were provided by HKEPD at three sites: Tung Chung (TC), Mong Kok (MK), and Cape D’Aguilar Supersite (CDSS), where TC and MK repersent urban area and CDSS repersents rural area.
The results showed a decrease of major pollutants from 2001 to 2020; however, O3 was increased from 6.15% to 22.20% and 25.98% to 51.24% for general monitoring stations and roadside monitoring stations, respectively. Furthermore, we showed that O3 experienced highest increase in November 2019 and April 2020 comparing with 2017-2019. The ozone formation mechanism was applied to identify the source of increased O3 by calculating the VOC/NOx ratio. The results indicated that stronger local formation of O3 was the main reason for the increase before the pandemic, while importation was predominant in April. The NOx titration effect is expected to contribute to local formation of ozone.
Land Use Regression (LUR) model has been widely used for modelling spatial distribution in city scale air pollution issues, but few have conducted in Japan. To study spatial distribution of pollutants, the Kriging method is commonly used but it is highly constrainted by the sparseness of monitoring sites. Therefore, we developed LUR models for the assessment of PM2.5, NOx, Ox, and SO2 in Tokyo 23 wards, by utilizing GIS data in Japan.
The 2016 land use data with 100x100 m2 resolution were collected from Japanese Ministry of Land, Infrastructure, Transport and Tourism (MILT); meanwhile, the air pollution data were collected via Japanese air monitoring system AEROS, including annual mean PM2.5 (μg/m3), NOx (ppb), daytime 1-hour Ox (ppb), and SO2 (ppb) data collected by 84, 84, 46, and 33 air monitoring stations in 2016. To develope regression equation, we applied multiple linear regression with stepwise selection of the prediction variables. The variables were selected based on AIC value. The models were validated by leave-one-out validation (LOOV) method.
The resulting models performed adjusted R2 values for PM2.5, NOx, Ox, and SO2 of 0.41, 0.37, 0.84, and 0.55, respectively. The root-mean-squared errors (RMSE) for PM2.5, NOx, Ox, and SO2 LUR models were 0.93 μg/m3, 7.81 ppb, 1.05 ppb, and 0.48 ppb. The results showed that high-rise building and dense road map in the center of Tokyo contributes to accumulation of air pollutions. Meanwhile, the ozone concentration in Tokyo is largely affected by the area of vegetation; therefore, BVOC is believed to be one major limiting species for ozone formation in Tokyo.
With increasing environmental concern on air pollution, various strategies to tackle air pollution have been widely implemented. The indoor air pollution in Japanese subway system has provoked public awareness. Previous studies showed that the iron-containing particles are dominant in the subway system. Hence, this study aims at discovering the efficiency of magnetic tubes for removal of iron-containing particles. In the study three different tubes are used: empty, weak magnetic and strong magnetic (SmCo. The results showed that SmCo magnetic tube contributed to 22.4% to 57.5% removal of iron particles, and the weak magnetic tube contributed to a decline of 6.5% to 19.5% of iron particles after a 7-day measurement. Furthermore, the results showed that the SmCo magnetic tube performed 15% removal efficiency of particles with diameter between 0.583 to 0.724 μm; however, no significant performance was recorded for particle smaller than 0.3652 μm. Further study may focus on the investigation of the efficiency of SmCo magnetic tube by amplifying the magnetic flux density.
In past decades, researchers reported special trends in global solar radiation, which some developing countries have experienced obvious drop. This study reported the solar dimming and brightening from 1968 to 2018 in Hong Kong and part of the Pearl River Delta (PRD) region. In the study areas, solar radiation decreased from 1960s to 1990s and bounced back until 2018. Similar trends were reported by nearby developing regions and countries, such as Japan and Shanghai. The improvement of air quality was estimated to be the main reason for the solar brightening. This study aims at exploring the characteristics of such solar radiation trend in the region. We hypothesized that the importation from mainland China and local SOA formation in the past accounted for majority of the particulate matters (PM), in which fine particles further facilitated local cloud formation. The results showed that solar dimming and brightening were obvious in the spring for Hong Kong, Shantou, and Guangzhou, but uncertain for Macau due to limitation in data acquisition. Furthermore, springtime cloud amount showed similar trend in Hong Kong. Further study may focus on quantifying the contribution of solar brightening to global warming and the effect of wind stilling in China on aerosol transportation and deposition.
