From direct emission factors to inverse and indirect impact factors of road traffic: influence of emerging and unregulated pollutants
- 1Tampere University (Tampere, Finland)
Abstract
Even though emissions regulations have successfully reduced concentrations of some road traffic-originated air pollutants, road traffic is still an important source of many unregulated emerging pollutants such as semi-volatile ultrafine particles, non-exhaust emissions and volatile organic compounds (VOCs) in urban areas. In addition, road traffic can have season- and location-dependent inverse and indirect effects on the urban aerosol which are not well understood. In our study, we investigate wintertime vehicle fleet emission factors (EF) of road traffic in a street canyon environment in central Helsinki, Finland, by using CO ₂ as a tracer for fuel consumption. We report EFs for particle number and size distribution, black carbon, PM ₁₀ , PM 2.5 , NO x , NO ₂ , NO, CO as well as for organic and inorganic chemical components of particulate matter, and VOCs, including aromatic hydrocarbons, alkanes, and polycyclic aromatic hydrocarbons. The obtained fleet EFs of PM and NO x were considerably higher than required for new vehicles in Europe since 2014, showing the major role of older vehicles and heavy-duty traffic on the urban aerosol. In addition to direct EFs, we show that CO ₂ -based EF determination enables detection of inverse and indirect effects of road traffic. For example, road traffic had an inverse effect, i.e., negative EF, on O ₃ and small ion (<2 nm) concentrations. Also, we found that road traffic contributes to compounds that are not necessarily considered to be traffic-derived such as terpenoid VOCs. We introduce a term impact factor (IF) to describe the found inverse and indirect effects of road traffic.
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BibTeX
@article{savolainen2026from,
title = {{From direct emission factors to inverse and indirect impact factors of road traffic: influence of emerging and unregulated pollutants}},
author = {Lauri K. Savolainen and Teemu Lepistö and Heidi Hellén and Henna Lintusaari and Milja Jäppi and Jarkko V. Niemi and Kimmo Teinilä and Minna Aurela and Markus Lampimäki and Anu Kousa and Janne Lampilahti and Katrianne Lehtipalo and Tuukka Petäjä and Miikka Dal Maso and Hanna E. Manninen and Hilkka Timonen and Topi Rönkkö},
journal = {Atmospheric Chemistry and Physics},
year = {2026},
month = oct,
doi = {10.5194/acp-26-14823-2026},
url = {https://acp.copernicus.org/articles/26/14823/2026/},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - From direct emission factors to inverse and indirect impact factors of road traffic: influence of emerging and unregulated pollutants
AU - Lauri K. Savolainen
AU - Teemu Lepistö
AU - Heidi Hellén
AU - Henna Lintusaari
AU - Milja Jäppi
AU - Jarkko V. Niemi
AU - Kimmo Teinilä
AU - Minna Aurela
AU - Markus Lampimäki
AU - Anu Kousa
AU - Janne Lampilahti
AU - Katrianne Lehtipalo
AU - Tuukka Petäjä
AU - Miikka Dal Maso
AU - Hanna E. Manninen
AU - Hilkka Timonen
AU - Topi Rönkkö
PY - 2026
DA - 2026/10/22
JO - Atmospheric Chemistry and Physics
DO - 10.5194/acp-26-14823-2026
UR - https://acp.copernicus.org/articles/26/14823/2026/
AB - Even though emissions regulations have successfully reduced concentrations of some road traffic-originated air pollutants, road traffic is still an important source of many unregulated emerging pollutants such as semi-volatile ultrafine particles, non-exhaust emissions and volatile organic compounds (VOCs) in urban areas. In addition, road traffic can have season- and location-dependent inverse and indirect effects on the urban aerosol which are not well understood. In our study, we investigate wintertime vehicle fleet emission factors (EF) of road traffic in a street canyon environment in central Helsinki, Finland, by using CO ₂ as a tracer for fuel consumption. We report EFs for particle number and size distribution, black carbon, PM ₁₀ , PM 2.5 , NO x , NO ₂ , NO, CO as well as for organic and inorganic chemical components of particulate matter, and VOCs, including aromatic hydrocarbons, alkanes, and polycyclic aromatic hydrocarbons. The obtained fleet EFs of PM and NO x were considerably higher than required for new vehicles in Europe since 2014, showing the major role of older vehicles and heavy-duty traffic on the urban aerosol. In addition to direct EFs, we show that CO ₂ -based EF determination enables detection of inverse and indirect effects of road traffic. For example, road traffic had an inverse effect, i.e., negative EF, on O ₃ and small ion (<2 nm) concentrations. Also, we found that road traffic contributes to compounds that are not necessarily considered to be traffic-derived such as terpenoid VOCs. We introduce a term impact factor (IF) to describe the found inverse and indirect effects of road traffic.
SN - 1680-7324
ER -