ICOS Science Conference, Session 7

1. Tracking the Nature of
Urban Carbon Cycle
the introduction of Megacity CO2 - Seoul Project
ICOSScienceConference2020
Chaerin Park, Sujong Jeong
crplove@snu.ac.kr
Seoul National University, Seoul, Korea

2. A table of Contents
Part1
Introduction of the project
“Megacity CO2 – Seoul” Part2
The preliminary results
using flux measurements
2

3. Part 1
Megacity CO2 - Seoul Project
Observation Network Modeling System
 Inverse Modeling :
WRF-STILT
 Biogenic Carbon Flux Modeling :
SNU-DECO
(SNU Data based ECOsystem model)
Inventory
 CO2 Concentration Observation
 CO2 Flux Observation
 Hourly 1 km resolution data
3

4.  CO2 Concentration Observation
2 low-cost observation sites
3 high-cost observation sites
 FTIR Remote Sensing Analyzer
2 EM27/Sun observation sites
 CO2 Flux Tower Observation
14 flux-tower observation sites
Megacity CO2 - Seoul ProjectPart 1
Ground Observation Network
4

5.  SNUCO2M
- Low-cost equipment using LI-850 sensor has been developed
- Has only a 0.71% of error range
 2 low-cost observation sites (NSTH, YSB) at different altitude
- Study on the difference in CO2 characteristics by altitude is in progress
Megacity CO2 - Seoul ProjectPart 1
CO2 Concentration Observation (low-cost)
5
NSTH
YSB
Seoul National University CO2 Measurement
(SNUCO2M)
Park et al., 2020

6.  3 high-cost observation sites (NSTL, OLY, GWA)
- Urban sites (NSTL, OLY)
- Urban background site (GWA)
Megacity CO2 - Seoul ProjectPart 1
CO2 Concentration Observation (high-cost)
6
Picarro G2131-i
Park et al., 2020

7.  2 EM27/SUN spectrometer at Seoul National University
- Continuous stationary observation &
Mobile observation around Seoul area will be carried
- Collaboration with GOSAT satellite team is also
underway (GOSAT 2nd RA selected)
Megacity CO2 - Seoul ProjectPart 1
FTIR Remote Sensing Analyzer
7
EM27/SUN spectrometer
Seoul National University
EM27/SUN Series
Lat/Lon:37.462/126.954
 Observations will continue for more than 10
years

8. Megacity CO2 - Seoul ProjectPart 1
CO2 Flux Tower Observation
8
CO2 and H2O open-path gas analyzer (EC150, CSI)
3-D sonic anemometer (CSAT3A, CSI)
 14 flux-tower observation sites within Seoul Capital Area
- Observations are made in different urban land type such as
vegetation, residential, and commercial areas
- Flux network has been established since 2014 with
automatic weather system

9. Part 2
Tracking the Nature of Urban Carbon Cycle
Using Flux Measurements
9
Method (Data Preprocessing)
Fourteen Flux
Tower sites
measurements
from 2014
Gap Filling
Step 1
Removing rainy time data
Step 2
Removing night time data with negative value
Step 3
Removing machine malfunction data manually
Step 4
Removing major outlier statistically
Step 5
Removing a data lower than the baseline site
Raw Data Data Filtering
Short missing (< 2hr)
Filling data with linear interpolation
Long missing (< 2day)
Filling data with the mean diurnal
data

10. Part 2
Tracking the Nature of Urban Carbon Cycle
Using Flux Measurements
10
Method (Data Preprocessing)
Data
Preprocessing
 Only 9 sites with more than 80% data remaining after
filtering were used for final analysis
 Analysis was performed using 2017 ~ 2018 data,
which is the period during which continuous
observation was best performed at all observation
sites.
JNG
SGD
ILS
GJW
NOW
GHM
GAN
ANY SGN

11. Part 2
Tracking the Nature of Urban Carbon Cycle
Using Flux Measurements
11
 Baseline site
- SGD
 Vegetation site
- ILS
JNG
SGD
ILS
GJW
NOW
GHM
GAN
ANY SGN
 Urban site
Commercial site
- NOW, GHM, GAN, ANY
Residential site
- JNG, GJW (new town), SGN (old town)
JNGILS
SGD SGN

12. Part 2
Tracking the Nature of Urban Carbon Cycle
Using Flux Measurements
12
Spatial distribution chart of each site with averaged CO2 concentration (a) and flux data (b)
from 2017 to 2018.
 SGD site is located near the ocean and show the lowest CO2 concentration (411 ppm)
and flux value (4106 g CO2/m2year)
 Each site within the Seoul capital area has highly different flux values
(range: 4106 ~ 59980 g CO2/m2year)

13. Part 2
관측지 설명
13
Tracking the Nature of Urban Carbon Cycle
Using Flux Measurements
Time series of monthly averaged CO2 flux for each site (left) and CO2 flux bar graph drawn with average
values from 2017 to 2018 (right).
 Baseline site (SGD:4106 g CO2/m2year) < Vegetation site (ILS:6078 g CO2/m2year ) < Urban site (SGN: 59980 g CO2/m2year)
- On average, urban area produces more than seven times CO2 flux than the baseline area and four times than
the vegetation area
- Old town residential area produce 3 times more CO2 flux than that of new town

14. Part 2
관측지 설명
14
Tracking the Nature of Urban Carbon Cycle
Using Flux Measurements
Time series of monthly averaged CO2 flux for each site (left) and CO2 flux bar graph drawn with average
values from 2017 to 2018 (right).
 Seasonal variability that is low at summer (August: 36 g CO2/m2day) and high in winter (January: 103 g CO2/m2day) is shown
- CO2 emissions in winter time are three times higher than in summer time
- July, when the temperature is highest, emits more CO2 than June and August

15. Part 2
15
Tracking the Nature of Urban Carbon Cycle
Using Flux Measurements
Diurnal time series of CO2 flux for each site during summer (a) and winter (b).
 Summer time
- Only baseline site (SGD: -0.097 g CO2/m2hour) and vegetation site (ILS: -1.33 g CO2/m2hour) show negative flux during the
day
- Commercial and residential sites have increased flux during the day than night
 Winter time
- All sites act as emission sources showing positive flux in all time zones

16. Part 2
16
Tracking the Nature of Urban Carbon Cycle
Using Flux Measurements
Heat map of correlation coefficient matrix between the
selected variables with each site during summer (a) and
winter (b).
 Temperature (weather variable), floating population and traffic
(variables of human activity) are highly correlated with flux in
most site
- Vegetation site (ILS) has negative correlation with
temperature because of vegetation activity
- Residential site (JNG, GJW) has negative correlation with
floating population as they have opposite diurnal pattern of
floating population compared to commercial site
FloatingPopulation
FloatingPopulation
Hour (LST) Hour (LST)
Residential Commercial

17. Part 2
17
Tracking the Nature of Urban Carbon Cycle
Using Flux Measurements
Scatter plot of CO2 flux with temperature for urban site
(black) and vegetation site (red). Each solid line represents
the median value of all urban site and vegetation site,
respectively. The grey vertical lines represent standard
temperature of heating and cooling, respectively.
 The CO2 flux significantly increases as the temperature
decreases
 CO2 flux from the urban sites increases when the
temperature rises above 20 ℃
- Considered to be the cooling effect
- July, which has the highest temperature in Seoul, has a
higher CO2 flux than June and August
 CO2 flux from the vegetation site (ILS) decreases when
the temperature rises above 20 ℃
- Considered to be the active vegetation activity
 As the temperature rises, the greater the difference in CO2
emissions between vegetation and urban areas

18. Part 2
18
Tracking the Nature of Urban Carbon Cycle
Using Flux Measurements
Summary
 To quantifying and finding the exact CO2 emission and sink source from Seoul Capital area, we established
Megacity CO2 - Seoul Project
 Urban area produces more than seven times CO2 flux (27023 g CO2/m2year) than that of the urban background
area (4106 g CO2/m2year)
 There is high CO2 flux variability within one city (range: 4106 ~ 59980 4106 g CO2/m2year)
 Urban area has three times higher CO2 flux in winter (103 g CO2/m2day) than in summer (36 g CO2/m2day) , and
even in summer daytime, they act as an emission source for all time zones
 Urban CO2 flux is highly correlated with temperature and human activity such as floating population and traffic
volume
 CO2 flux of urban sites increases as the temperature decreases under 20 ℃ & when the temperature increases
above 20 ℃, CO2 flux increases again
 CO2 flux of vegetation site increases as the temperature decreases under 20 ℃ & when the temperature
increases above 20 ℃, CO2 flux decreases

19. Thank you
19