Measurement report: The influence of traffic and new particle 
formation on the size distribution of 1–800 nm particles in Helsinki: 
a street canyon and an urban background station comparison

Okuljar, Magdalena; Kuuluvainen, Heino; Kontkanen, Jenni; Garmаsh, Olga; Olin, Miska; Niemi, Jarkko V.; Timonen, Hilkka; Kangasluoma, Juha; Tham, Yee Jun; Baalbaki, Rima; Sipilä, Mikko; Salo, Laura; Lintusaari, Henna; Portin, Harri; Teinilä, Kimmo; Aurela, Minna; Maso, Miikka Dal; Rönkkö, Topi; Petäj̈ä, Tuukka; Paasonen, Pauli

doi:10.5194/acp-2020-1282

Cited by 3 publications

(3 citation statements)

References 4 publications

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“…PMF factors and VOC data used for this study are available at https://doi.org/10.5281/zenodo.8273030 (Okuljar et al, 2023). SA, sub-3 nm particle concentration, and meteorological and trace gas data from the street canyon are available at https://doi.org/10.5281/zenodo.4884875 (Okuljar, 2021). Trace gas and meteorological data measured at the background station are available at the SmartSMEAR data repository (https://smear.avaa.…”

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confidence: 99%

Influence of anthropogenic emissions on the composition of highly oxygenated organic molecules in Helsinki: a street canyon and urban background station comparison

Okuljar,

Garmash,

Olin

et al. 2023

Atmos. Chem. Phys.

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Abstract. Condensable vapors, including highly oxygenated organic molecules (HOMs), govern secondary organic aerosol formation and thereby impact the quantity, composition, and properties (e.g., toxicity) of aerosol particles. These vapors are mainly formed in the atmosphere through the oxidation of volatile organic compounds (VOCs). Urban environments contain a variety of VOCs from both anthropogenic and biogenic sources, as well as other species, for instance nitrogen oxides (NOx), that can greatly influence the formation pathways of condensable vapors like HOMs. During the last decade, our understanding of HOM composition and formation has increased dramatically, with most experiments performed in forests or in heavily polluted urban areas. However, studies on the main sources for condensable vapors and secondary organic aerosols (SOAs) in biogenically influenced urban areas, such as suburbs or small cities, have been limited. Here, we studied the HOM composition, measured with two nitrate-based chemical ionization mass spectrometers and analyzed using positive matrix factorization (PMF), during late spring at two locations in Helsinki, Finland. Comparing the measured concentrations at a street canyon site and a nearby urban background station, we found a strong influence of NOx on the HOM formation at both stations, in agreement with previous studies conducted in urban areas. Even though both stations are dominated by anthropogenic VOCs, most of the identified condensable vapors originated from biogenic precursors. This implies that in Helsinki anthropogenic activities mainly influence HOM formation by the effect of NOx on the biogenic VOC oxidation. At the urban background station, we found condensable vapors formed from two biogenic VOC groups (monoterpenes and sesquiterpenes), while at the street canyon, the only identified biogenic HOM precursor was monoterpenes. At the street canyon, we also observed oxidation products of aliphatic VOCs, which were not observed at the urban background station. The only factors that clearly correlate (temporally and composition-wise) between the two stations contained monoterpene-derived dimers. This suggests that HOM composition and formation mechanisms are strongly dependent on localized emissions and the oxidative environment in these biogenically influenced urban areas, and they can also change considerably within distances of 1 km within the urban environment. This further suggests that studies should be careful when extrapolating single-point measurements in an urban setting to be representative of district or city scales.

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confidence: 99%

Influence of anthropogenic emissions on the composition of highly oxygenated organic molecules in Helsinki: a street canyon and urban background station comparison

Okuljar,

Garmash,

Olin

et al. 2023

Atmos. Chem. Phys.

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show abstract

“…Data availability. PMF factors and VOC data used for this study are available at https://doi.org/10.5281/zenodo.8273030 (Okuljar et al, 2023). SA, sub-3 nm particle concentration, and meteorological and trace gas data from the street canyon are available at https://doi.org/10.5281/zenodo.4884875 (Okuljar, 2021).…”

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confidence: 99%

mentioning

confidence: 99%

Influence of anthropogenic emissions on the composition of highly oxygenated organic molecules in Helsinki: a street canyon and urban background station comparison

Okuljar

Garmаsh

Olin

et al. 2023

Preprint

View full text Add to dashboard Cite

Abstract. Condensable vapors, including highly oxygenated organic molecules (HOM), govern secondary organic aerosol formation and thereby impact the amount, composition, and properties (e.g. toxicity) of aerosol particles. These vapors are mainly formed in the atmosphere through the oxidation of volatile organic compounds (VOCs). Urban environments contain a variety of VOCs from both anthropogenic and biogenic sources, as well as other species, for instance nitrogen oxides (NOx), that can greatly influence the formation pathways of condensable vapors like HOM. During the last decade, our understanding of HOM composition and formation has increased dramatically, with most experiments performed in forests or in heavily polluted urban areas. However, studies on the main sources for condensable vapors and secondary organic aerosols (SOA) in biogenically influenced urban areas, such as suburbs or small cities, has been limited. Here, we studied the HOM composition, measured with two nitrate-based chemical ionization mass spectrometers and analyzed using positive matrix factorization (PMF), during late spring at two locations in Helsinki, Finland. Comparing the measured concentrations at a street canyon site and a nearby urban background station, we found a strong influence of NOx on the HOM formation at both stations, in agreement with previous studies conducted in urban areas. Even though both stations are dominated by anthropogenic VOCs, most of the identified condensable vapors originated from biogenic precursors. This implies that in Helsinki anthropogenic activities mainly influence HOM formation by the effect of NOx on the biogenic VOC oxidation. At the urban background station, we found condensable vapors formed from two biogenic VOC groups (monoterpenes and sesquiterpenes), while at the street canyon, the only identified biogenic HOM precursor was monoterpenes. At the street canyon, we also observed oxidation products of aliphatic VOCs, which were not observed at the urban background station. The only factors that clearly correlate (temporally and composition-wise) between the two stations contained monoterpene-derived dimers. This suggests that HOM composition and formation mechanisms are strongly dependent on localized emissions and the oxidative environment in these biogenically influenced urban areas, and they can change considerably also within distances of one kilometer within the urban environment.

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Measurement report: The influence of traffic and new particle formation on the size distribution of 1–800 nm particles in Helsinki – a street canyon and an urban background station comparison

et al. 2021

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Abstract. Most of the anthropogenic air pollution sources are located in urban environments. The contribution of these sources to the population of atmospheric particles in the urban environment is poorly known. In this study, we investigated the aerosol particle number concentrations in a diameter range from 1 to 800 nm at a street canyon site and at a background station within 1 km from each other in Helsinki, Finland. We use these number size distribution data together with complementary trace gas data and develop a method to estimate the relative contributions of traffic and atmospheric new particle formation (NPF) to the concentrations of sub-3 nm particles. During the daytime, the particle concentrations were higher at the street canyon site than at the background station in all analyzed modes: sub-3 nm particles, nucleation mode (3–25 nm), Aitken mode (25–100 nm), and accumulation mode (100–800 nm). The population of sub-3 nm and nucleation mode particles was linked to local sources such as traffic, while the accumulation mode particles were more related to non-local sources. Aitken mode particles were dominated by local sources at the street canyon site, while at the background station they were mainly influenced by non-local sources. The results of this study support earlier research showing direct emissions of the sub-3 nm particles from traffic. However, by using our new method, we show that, during NPF events, traffic contribution to the total sub-3 nm particle concentration can be small and during daytime (6:00–20:00) in spring it does not dominate the sub-3 nm particle population at either of the researched sites. In the future, the contribution of traffic to particle number concentrations in different urban environments can be estimated with a similar approach, but determining the relationships between the gas and particle concentrations from observations needs to be conducted with longer data sets from different urban environments.

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Measurement report: The influence of traffic and new particle formation on the size distribution of 1–800 nm particles in Helsinki: a street canyon and an urban background station comparison

Cited by 3 publications

References 4 publications

Influence of anthropogenic emissions on the composition of highly oxygenated organic molecules in Helsinki: a street canyon and urban background station comparison

Influence of anthropogenic emissions on the composition of highly oxygenated organic molecules in Helsinki: a street canyon and urban background station comparison

Influence of anthropogenic emissions on the composition of highly oxygenated organic molecules in Helsinki: a street canyon and urban background station comparison

Measurement report: The influence of traffic and new particle formation on the size distribution of 1–800 nm particles in Helsinki – a street canyon and an urban background station comparison

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