�Improved understanding of PM_2.5 in Korea and China �through integrated modeling and analysis of satellite, aircraft, and surface observations�

�Daniel Jacob

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Samsung PM_2.5 Strategic Research Program

Year 3 Report

Shixian Zhai

Laura Yang

Brewer, J.F., D.J. Jacob, S.H. Jathar, Y. He, A. Akherati, S. Zhai, D.S. Jo, A. Hodzic, B.A. Nault, P. Campuzano-Jost, J.L. Jimenez, R.J. Park, Y.J. Oak, and H. Liao, A scheme for representing aromatic secondary organic aerosols in chemical transport models: application to source attribution of organic aerosols over South Korea during the KORUS-AQ campaign, J. Geophys. Res., e2022JD037257, 2023.

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Colombi, N. K., Jacob, D. J., Yang, L. H., Zhai, S., Shah, V., Grange, S. K., Yantosca, R. M., Kim, S., and Liao, H.: Why is ozone in South Korea and the Seoul Metropolitan Area so high and increasing?, Atmos. Chem. Phys., 23, 4031–4044, 2023.

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Yang, L.H., D.J. Jacob, N.K. Colombi, S. Zhai, K.H. Bates, V. Shah, E. Beaudry, R.M. Yantosca, H. Lin, J.F. Brewer, H. Chong, K.R. Travis, J.H. Crawford, L. Lamsal, J.-H. Koo, and J. Kim, Tropospheric NO₂ vertical profiles over South Korea and their relation to oxidant chemistry: Implications for geostationary satellite retrievals and the observation of NO₂ diurnal variation from space, Atmos. Chem. Phys., 23, 2465–2481, 2023.

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Zhai, S., Jacob, D. J., Pendergrass, D. C., Colombi, N. K., Shah, V., Yang, L. H., Zhang, Q., Wang, S., Kim, H., Sun, Y., Choi, J.-S., Park, J.-S., Luo, G., Yu, F., Woo, J.-H., Kim, Y., Dibb, J. E., Lee, T., Han, J.-S., Anderson, B. E., Li, K., and Liao, H.: Coarse particulate matter air quality in East Asia: implications for fine particulate nitrate, Atmos. Chem. Phys., 23, 4271–4281, 2023.

Nadia Colombi

Simulation of organic aerosol observations during KORUS-AQ (May-June 2016)

GEOS-Chem model

• New SOM-VBS scheme for aromatic and S/IVOC SOA can reproduce observations much better than standard GEOS-Chem schemes
• Oxidized POA, aromatic SOA, S/IVOC SOA are the main components
• New scheme is now slated to go into the standard GEOS-Chem

Brewer et al. [2023]

Contributions to surface organic aerosol over Korea

from GEOS-Chem simulations with SOM-VBS scheme (May-Jun 2016)

baseline simulation

no anthro. emissions in Korea

no anthro. emissions anywhere

OA over Korea is ≈ 1/3 biogenic, 1/3 domestic anthropogenic, 1/3 foreign anthropogenic

Brewer et al. [2023]

Mean OA over Korea

Why is ozone over Korea so high and increasing?

2016

• Increase is largest in May
• GEOS-Chem with 22% decrease in NO_x emissions (based on NO₂ data) can capture the ozone levels and trend

Colombi et al. [2023]

mean value for Korea

Further analysis of ozone sources over East Asia in May

Circles: observed 90^th percentile MDA8

Background: GEOS-Chem

• East Asia background ozone (originating from outside) is extremely high, prevents attainment of air quality standard
• Even if Korea or China emissions were zeroed ozone would still approach 80 ppb

Colombi et al. [2023]

Observing the diurnal cycle of NO₂ from GEMS satellite instrument

Hourly geostationary observations inform NO_x emissions, chemistry, transport

slant column density (SCD)

vertical column density (VCD)

Air mass factor

geometric correction

scattering weight (sensitivity)

vertical shape factor

NO₂ VCD, 10¹⁶ molecules cm^-2

Local time, hours

JJA 2021

Park et al., submitted

all depend on time of day

z_T

TROPOMI

Hanlim Lee (PKNU)

Diurnal variation of AMF driven by mixed layer growth

Ensemble of KORUS-AQ aircraft profiles over Seoul (May-June 2016)

20% diurnal variation from scattering correction factor

Yang et al. [2023]

Variability of AMF for KORUS-AQ vertical profiles

As calculated from observed and simulated (GEOS-Chem) vertical shape factors

• 50% variability in AMF mainly driven by land vs. ocean, time of day for land
• Largest model error is in timing of morning mixed layer growth: difficult to get right!

Yang et al. [2023]

Error in timing of mixed layer growth

AMF error

Error in retrieved diurnal cycle

Coarse PM trends from air quality networks, 2015-2020

• Decreasing emissions from construction sites and road dust

Zhai et al., 2023

Coarse PM = PM₁₀ – PM_2.5

Road dust

Construction

Coarse anthropogenic dust suppresses PM_2.5 nitrate formation

NO_x

HNO₃

coarse NO₃^-

NO_x emission

dust emission

PM_2.5 NO₃^-

oxidation

uptake

• Emitted dust particles are alkaline, take up HNO₃ efficiently
• The resulting coarse NO₃^- is eventually deposited

NH₃ emission

Zhai et al., 2023

Decreasing coarse PM can partly explain flat PM_2.5 nitrate in winter

despite 2015-2021 NO_x emission decreases of ~30% in China and Korea

Additional factors are flat ammonia emissions and increased ozone

Zhai et al. , 2023

Work in progress

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• Ellie Beaudry: ethanol and methanol in China and South Korea as indicators of large emissions of volatile chemical products (VCPs)

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• Nadia Colombi: origin of the elevated ozone background over East Asia

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• Ruijun Dang: Satellite NH₃/NO₂ ratios as indicator of chemical regime for PM_2.5 nitrate formation

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• Yujin Oak: blended GEMS+TROPOMI NO₂ satellite product for analyzing diurnal cycles and inferring NO_x emissions

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• Drew Pendergrass: intepretation of recent PM_2.5 trends in Korea

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• Drew Pendergrass: updated PM_2.5 mapping over East Asia from new 2x2 km² GOCI AOD data

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• Laura Yang: Drivers of elevated methylhydroperoxide in urban air over Korea

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Ellie Beaudry

Ruijun Dang

Yujin Oak

Drew Pendergrass