Measuring megacity air by Miikka Dal Maso and Craes

Measuring megacity air

Miikka Dal Maso1, Anssi Järvinen1, Antti Rosted1, Jian Gao2, Topi Rönkkö1

1Tampere University of Technology, Tampere, Finland2CRAES, Beijing, China

04/15/2023 2

Improving urban air quality – a challenge on many fronts

2015 - Miikka Dal Maso

Understanding and improving urban air quality requires a holistic approach in which all critical aspects are taken into account. At TUT, our focus is measuring emissions and concentrations and modeling transformation at high scientific quality.

TUT FOCUS TUT FOCUS

Roadmap to Beautiful Beijing/Beautiful China

04/15/2023 3

Challenges of measuring aerosol in (mega)cities

Particle Diameter (nm)1 10 100 1000

107

105

103

101

10000

Sulfuric Acid

Organic

Nitrate

Carbonaceous

Sulfate

Sea Salt

Mineral


Urban PM, with multiple source components, also exhibits high physical and chemical complexity

Example of urban aerosol complexity: Beijing size distribution data shows six different typical size distributions. Half the time, more than 50% of particles are <50 nm.

Beijing

Particle size

Pa

rtic

le n

um

be

r (n

orm

.)

Gao, Dal Maso et al, in prep.

04/15/2023 4

TUT researches city aerosol on several fronts


1. Targeted urban measurements 2. Instrument development

4. Process studies - modeling3. Fresh and aged emissionmeasurements

04/15/2023

MMEA (Measurement, Monitoring and Environmental Efficiency Assessment) aerosol

reseach environment

5

• Measurement methods, instrument development

• Calibrations, field tests• Emission studies• Data intercomparisons• Air quality studies


6

What is needed for urban aersol measurement?


Requirements for urban aerosol physical characterization:• small and large particles,

number and volume (mass) • high time resolution• high spatial density of

measurement sites – low price• low maintenance

Understanding of physics and chemistry, and sources

Gathering and analysis of heterogeneous urban-scale data

04/15/2023

Image: ENFUSER example

In urban areas, pollutants are not distributed evenly, and concentrations depend on source proximity

04/15/2023 7

China Testbed instrument: Pegasor PPS-M sensor


Diffusion charger based aerosol sensors (e.g. Pegasor PPS-M) are good fit for presented requirements:• Affordable, small, robust,

repeatable, easy to use• potential for extracting size-

dependency information• number and mass

• can cover wide size range

04/15/2023

• Overview– Diffusion charging

+ electrical detection– Non-collective instrument– Applications: Emissions,

air quality, portable systems...

• Components– Pre-cut cyclone – Ion source– Charging region– Ejector pump– Mobility analyser

8

PPS-M sensor

Sample inlet

Sensor exhaust

Pressurizedair inlet


04/15/2023

Calibration of PPS-M at TUT

2015 - Miikka Dal Maso 9

Aim of calibration is to find response function by particle size and mobility analyser voltage

CPC is the reference instrument which has been calibrated electrically

CPC is used because neutral particles are preferred in charger calibrations

Rostedt et al. 2014

Electrically neutral particles

04/15/2023 10

Developed PPS-M response function


Overall response Polydisperse test

Out p p pS R d N d dd

Rostedt et al., 2014Optimal size response for combustion originating particles

Charging efficiency, mobility analyzer, diffusion, inertial losses

, , ,p ma ch p ma ma p ma d p i pR d V E d V P d V P d P d

04/15/2023 11

Field measurements with PPS-M in Finland


Number concentration

PPS-M shows good correlations with PM2.5 in residential area and roadside, and also good number correlations.China testbed research question: Can we get more information?

Järvinen et al, 2014

PM2.5 Mass concentration

04/15/2023

Field measurements with PPS-M in China


Server in China

Server in Finland

Pressurized airDroplet separation

PPS internal heating

Insulation

Inlet heating

• PPS-M sensor installed at the CRAES measurement station

• Continuous measurements from Feb-Nov 2014

• Comparisons with long-term observations of performed at CRAES

• Data logged locally and transferred via network

• Data covers many different situations of polluted urban air

Gao, Dal Maso et al., 2015 (in prep)

04/15/2023

PPS-M Number and Mass response in highly polluted air


PPS-M response dependency on mobility analyser voltage can be used to gain information on the mass-number relationship.

We have used measurements in Beijing to test the mobility analyser in real polluted megacity air.

Signal ratio

Mas

s/N

umbe

r ra

tio

Reference

PPS-M fit w/ mobility analyservoltage cycling

Vo

lum

eN

um

ber

Gao, Dal Maso et al., 2015 (in prep)

04/15/2023 14

Summary

• We need good concentration measurements covering urban city environment

• Diffusion charging based sensors such as PPS-M fulfill many requirements for sensors

• We have developed a sensor response model for size and mobility analyzer dependence which has been verified by laboratory measurements

• In outdoor measurements in Finland and China we could get both mass and number information. Mobility analysis was added for measurements in China


04/15/2023 15

Thank you for your attention


1. Rostedt, A., Arffman, A., Janka, K., Yli-Ojanperä, J. & Keskinen, J. (2014) Characterization and Response Model of the PPS-M Aerosol Sensor, Aerosol Science and Technology, 48(10), p. 1022-1030, DOI: 10.1080/02786826.2014.951023

2. Järvinen A., Kuuluvainen H., Niemi J.V., Saari S., Dal Maso M., Pirjola L., Hillamo R., Janka K., Keskinen J., Rönkkö T. (2014). Monitoring urban air quality with a diffusion charger based electrical particle sensor, Urban Climate 10, doi:10.1016/j.uclim.2014.10.002

3. Gao, J,., Järvinen, A., Hui, L., Luo, D., Rönkkö, T., and Dal Maso, M. (2015): Urban air quality measurements in Beijing using a diffusion charger based electrical particle sensor, in preparation

References