EGU General Assembly 2020 EGU2020-8301

Evaluating the Potential of Satellite Measurements in Air Quality Monitoring: A Project for the Finnish Ministry of the Environment Henrik Virta, Anu-Maija Sundström, Iolanda Ialongo, and Johanna Tamminen Finnish Meteorological Institute, Space and Earth Observation Centre, Helsinki, Finland

1 Project description

• Aim: to evaluate what potential satellite measurements have in complementing traditional in situ air quality measurements. • Performance of current instruments evaluated using gridded maps and statistical comparisons with collocated in situ station measurements in Finland.

• Focus on NO2 measurements done by the TROPOMI instrument; SO2, CO, and aerosols also covered. • Commissioned by the Finnish Ministry of the Environment. • Study period: April 2018 to June 2019.

2 Nitrogen dioxide (NO2)

• Internationally recognized air pollutant (WHO, EU, USA). • Increases in concentrations linked to increased mortality. • Concentration limits set by law. • Mainly emitted from combus- tion engines, biomass burning, soil bacteria, and lightning.

Pixabay 3 TROPOMI instrument

• Launched in October 2017 aboard Sentinel-5 Precursor. • Part of EU’s Copernicus Earth monitoring programme. • Hyperspectral imager measuring NO2, O3, CH4, CO, SO2, CH2O, clouds, and aerosols. • Ground resolution 7x3.5km (5.5x3.5km as of August 2019).

Sentinel-5P. ESA/ATG medialab

4 Gridded maps ]

• TROPOMI Tropospheric NO Kovdor 2

2 - measurements oversampled (avg.) to 2.5x2.5 km grid between cm . 15.4.2018–30.6.2019. molec [

• Helsinki capital region stands out, Kostomuksha 2 as do the cities of Turku and Tampere (among the most populous in Finland). • Two light dots just east of northern Finland are the Russian mining Tampere Tropospheric NO Tropospheric towns of Kostomuksha and Kovdor. St. Petersburg Turku Helsinki 5 Weak winds (<3m s-1) Gridded maps ]

• If only measurements made during 2 weak winds are included, effect of - emissions transport is reduced cm . → sources of NO2 more visible. molec [

• Smaller towns now stand out, as 2 do main highways (e.g. between Helsinki and Tampere). • Wind: ERA5 reanalysis product used to calculate average boundary layer wind speed. Tropospheric NO Tropospheric

6 Need of new Helsinki capital region stations?

• TROPOMI Tropospheric NO2 ] 2 oversampled (averaged) to -

1x1km grid. Helsinki-Vantaa airport cm .

• Highest concentrations near Ring III molec

Ring I [

Helsinki-Vantaa airport and just 2 north of Helsinki city centre. • Ring I Finland’s busiest road: not clearly visible on map

→ due to TROPOMI ovp time? NO Tropospheric

Permanent AQ stations marked by filled circles, 7 temporary stations by hollow circles. TROPOMI overpass time 19.4.2018–30.6.2019 Helsinki, Mäkelänkatu 70 Middle 50% • TROPOMI on an afternoon Hourly averages 60 Time series avg. orbit: overpasses between TROPOMI ovps. ] morning and afternoon peaks -3 50

in NO2 due to commuter traffic 40 → highest concentrations not captured, measurements 30 concentration [µg m represent ~midday average. 2 20 NO

• Important to remember when 10 interpreting measurements! 0 01 03 05 07 09 11 13 15 17 19 21 23 Finnish time

A classic example of the NO2 diurnal cycle from the Mäkelänkatu air quality station. TROPOMI overpass 8 times marked with grey vertical lines. TROPOMI vs. air quality stations

AveragePääkaupunkiseudun of different Helsinki asemien AQ keskiarvo stations • Correlation of TROPOMI and air 1015 R=0.1439, N=9 3.3 quality station measurements Pirkkola ] ] 2

2 3.2 evaluated using scatter plots. - • Collocation criteria: TROPOMI . cm 3.1 Tikkurila [molek./cm Kumpula 2

molec 3 pixels above station chosen, [ station measurements linearly 2 Kallio 2 Mäkelänkatu 2.9 Mannerheimintie interpolated to overpass time. Leppävaara 2.8 • Poor correlation of collocated 2.7 Luukki meas. averages: only ~0.14 2.6 TROPOMI Trop. NO TROPOMITrop. TROPOMI alailmakehän NO Vartiokylä 2.5 0 10 20 30 40 9 Ilmanlaatuaseman NO [µg/m-33] AQ station NO2 [µg2 m ] City centre aggregation

• Measurement aggregation by AverageKeskustan of Finnish mittausasemien city centre keskiarvo AQ stations 1015 R=0.7448, N=9 averaging together all city centre 3.2 Vantaa ] ] 3 2 2 stations. - Helsinki 2.8 Espoo • Correlation improved: ~0.74 . cm 2.6 [molek./cm 2 molec • TROPOMI pixels cannot capture [ 2.4 2

variability within a small area 2.2 such as city centre → poor corre- 2 lation with individual stations. Tampere 1.8 Turku

• Better correlation when 1.6 Rauma Pori

comparing city centres. NO TROPOMITrop. TROPOMI alailmakehän NO 1.4 Oulu Raahe 1.2 5 10 15 20 25 10 3 Ilmanlaatuaseman NO [µg/m-3 ] AQ station NO2 [µg2 m ] Effect of boundary layer wind

AverageKeskustan of mittausasemiencity centre AQ stationskeskiarvo (<3m (<3m/s) s-1) • Advection of NO2 emissions 1015 R=0.788, N=9 affects correlation by 5.5 ]

] Helsinki 2 2 dispersing emissions over a - 5 Espoo larger area. Vantaa . cm 4.5

• If only measurements during [molek./cm 2 molec 4 [

weak winds considered, 2 correlation is improved: ~0.79 3.5

• Northernmost studied city Oulu 3 Turku is outlier. May be due to snow Tampere 2.5 and ice cover (port city). Rauma 2 TROPOMI Trop. NO TROPOMITrop. TROPOMI alailmakehän NO Oulu Pori Raahe 1.5 5 10 15 20 25 30 11 3 Ilmanlaatuaseman NO [µg/m-3 ] AQ station NO2 [µg2 m ] Comparison of European cities

KeskustanAverage of mittausasemien city centre AQ keskiarvostations (<3m(<3m/s) s-1) • Study also extended to some 1015 R=0.9471, N=7 16 European cities. PariisiParis ] ] 2 2 • Data from European - 14 . cm LondonLontoo Environment Agency. 12 [molek./cm 2 molec [

• Data very well correlated: ~0.95 2 10

• Helsinki appears as a notable 8 HampuriHamburg outlier. Observed in situ vs. 6 TROPOMI differences require Helsinki further investigation. 4 TROPOMI Trop. NO TROPOMITrop. TROPOMI alailmakehän NO TallinnaTallinn TukholmaStockholm Oslo 2 30 40 50 60 70 12 3 Ilmanlaatuaseman NO [µg/m-3] AQ station NO2 2[µg m ] Conclusions

• TROPOMI oversampled grids a feasible tool to characterize regional spread of NO2 emissions and sources. • Could be used to plan placement of ground stations. • Overpass time of TROPOMI must be accounted for. • Correlation of TROPOMI and air quality station measurements between individual cities is good. • TROPOMI could be used as a tool to estimate NO2 concentrations in cities lacking any ground stations. • First such report delivered to the FME. • Societal interest in satellite measurements growing, thanks to TROPOMI’s unprecedented spatial resolution.

13 References Sundström, A.-M., Virta, H., Ialongo, I., and Tamminen, J., 2020: Satelliittihavaintojen hyödyntäminen ilmanlaadun seurannassa. Raportteja – Rapporter – Reports 2020:1, Finnish Meteorological Institute, Helsinki, Finland. doi: 10.35614/isbn.9789523360983 See also Ialongo, I., Virta, H., Eskes, H., Hovila, J., and Douros, J., 2020: Comparison of TROPOMI/Sentinel-5 Precursor NO2 product with ground-based observations in Helsinki and first societal applications. EGU2020-9963 at 7 May 2020, 8:30–10:15

7 May 2020 EGU2020-8301