A new oxidation flow reactor for measuring secondary aerosol formation of rapidly changing emission sources

Abstract. Oxidation flow reactors (OFRs) or environmental chambers can be used to estimate secondary aerosol formation potential of different emission sources. Emissions from anthropogenic sources, such as vehicles, often vary on short timescales. For example, to identify the vehicle driving conditions that lead to high potential secondary aerosol emissions, rapid oxidation of exhaust is needed. However, the residence times in environmental chambers and in most oxidation flow reactors are too long to study these transient effects ( ∼  100 s in flow reactors and several hours in environmental chambers). Here, we present a new oxidation flow reactor, TSAR (TUT Secondary Aerosol Reactor), which has a short residence time ( ∼  40 s) and near-laminar flow conditions. These improvements are achieved by reducing the reactor radius and volume. This allows studying, for example, the effect of vehicle driving conditions on the secondary aerosol formation potential of the exhaust. We show that the flow pattern in TSAR is nearly laminar and particle losses are negligible. The secondary organic aerosol (SOA) produced in TSAR has a similar mass spectrum to the SOA produced in the state-of-the-art reactor, PAM (potential aerosol mass). Both reactors produce the same amount of mass, but TSAR has a higher time resolution. We also show that TSAR is capable of measuring the secondary aerosol formation potential of a vehicle during a transient driving cycle and that the fast response of TSAR reveals how different driving conditions affect the amount of formed secondary aerosol. Thus, TSAR can be used to study rapidly changing emission sources, especially the vehicular emissions during transient driving.

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A New Oxidation Flow Reactor for Measuring Secondary Aerosol Formation of Rapidly Changing Emission Sources

10.5194/amt-2016-300 ◽

2016 ◽

Cited By ~ 3

Author(s):

Pauli Simonen ◽

Erkka Saukko ◽

Panu Karjalainen ◽

Hilkka Timonen ◽

Matthew Bloss ◽

...

Keyword(s):

Flow Reactor ◽

Anthropogenic Sources ◽

Emission Sources ◽

Transient Effects ◽

Aerosol Formation ◽

Flow Reactors ◽

Secondary Aerosol ◽

Formation Potential ◽

Environmental Chambers ◽

Driving Conditions

Abstract. Oxidation flow reactors or environmental chambers can be used to estimate secondary aerosol formation potential of different emission sources. Emissions from anthropogenic sources, such as vehicles, often vary on short timescales. For example, to identify the vehicle driving conditions that lead to high potential secondary aerosol emissions, rapid oxidation of exhaust is needed. However, the residence times in environmental chambers and in most oxidation flow reactors are too long to study these transient effects. Here, we present a new oxidation flow reactor, TSAR (TUT Secondary Aerosol Reactor), which has a short residence time and near-laminar flow conditions. This allows studying e.g. the effect of vehicle driving conditions on secondary aerosol formation potential of the exhaust. We show that the flow pattern in TSAR is nearly laminar and particle losses are negligible. The secondary organic aerosol (SOA) produced in TSAR has a similar mass spectrum as the SOA produced in the state-of-the-art reactor, PAM (Potential Aerosol Mass). Both reactors produce the same amount of mass, but the TSAR has a higher time-resolution. We also show that the TSAR is capable of measuring secondary aerosol formation potential of a vehicle during a transient driving cycle, and that the fast response of the TSAR reveals how different driving conditions affect the amount of formed secondary aerosol. Thus, the TSAR can be used to study rapidly changing emission sources, especially the vehicular emissions during transient driving.

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Organic peroxy radical chemistry in oxidation flow reactors and environmental chambers and their atmospheric relevance

10.5194/acp-2018-952 ◽

2018 ◽

Author(s):

Zhe Peng ◽

Julia Lee-Taylor ◽

John J. Orlando ◽

Geoffrey S. Tyndall ◽

Jose L. Jimenez

Keyword(s):

Flow Reactor ◽

Operating Conditions ◽

Peroxy Radicals ◽

Relative Importance ◽

Atmospheric Conditions ◽

Aerosol Formation ◽

Ambient Conditions ◽

Flow Reactors ◽

Environmental Chambers ◽

Atmospherically Relevant

Abstract. Oxidation flow reactors (OFR) are a promising complement to environmental chambers for investigating atmospheric oxidation processes and secondary aerosol formation. However, questions have been raised about how representative the chemistry within OFRs is of that in the troposphere. We investigate the fates of organic peroxy radicals (RO2), which play a central role in atmospheric organic chemistry, in OFRs and environmental chambers by chemical kinetic modeling, and compare to a variety of ambient conditions to help define a range of atmospherically relevant OFR operating conditions. For most types of RO2, their bimolecular fates in OFRs are mainly RO2+HO2 and RO2+NO, similar to chambers and atmospheric studies. For substituted primary RO2 and acyl RO2, RO2+RO2 can make a significant contribution to the fate of RO2 in OFRs, chambers and the atmosphere, but RO2+RO2 in OFRs is in general somewhat less important than in the atmosphere. At high NO, RO2+NO dominates RO2 fate in OFRs, as in the atmosphere. At high UV lamp setting in OFRs, RO2+OH can be a major RO2 fate and RO2 isomerization can be negligible for common multifunctional RO2, both of which deviate from common atmospheric conditions. In the OFR254 operation mode (where OH is generated only from photolysis of added O3), we cannot identify any conditions that can simultaneously avoid significant organic photolysis at 254 nm and lead to RO2 lifetimes long enough (~ 10 s) to allow atmospherically relevant RO2 isomerization. In the OFR185 mode (where OH is generated from reactions initiated by 185 nm photons), high relative humidity, low UV intensity and low precursor concentrations are recommended for atmospherically relevant gas-phase chemistry of both stable species and RO2. These conditions ensure minor or negligible RO2+OH and a relative importance of RO2 isomerization in RO2 fate in OFRs within ~ x2 of that in the atmosphere. Under these conditions, the photochemical age within OFR185 systems can reach a few equivalent days at most, encompassing the typical ages for maximum secondary organic aerosol (SOA) production. A small increase in OFR temperature may allow the relative importance of RO2 isomerization to approach the ambient values. To study heterogeneous oxidation of SOA formed under atmospherically-relevant OFR conditions, a different UV source with higher intensity is needed after the SOA formation stage, which can be done with another reactor in series. Finally, we recommend evaluating the atmospheric relevance of RO2 chemistry by always reporting measured and/or estimated OH, HO2, NO, NO2 and OH reactivity (or at least precursor composition and concentration) in all chamber and flow reactor experiments. An easy-to-use RO2 fate estimator program is included with this paper to facilitate investigation of this topic in future studies.

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Effects of Driving Conditions on Secondary Aerosol Formation from a GDI Vehicle Using an Oxidation Flow Reactor

Environmental Pollution ◽

10.1016/j.envpol.2021.117069 ◽

2021 ◽

pp. 117069

Author(s):

Niina Kuittinen ◽

Cavan McCaffery ◽

Weihan Peng ◽

Stephen Zimmerman ◽

Patrick Roth ◽

...

Keyword(s):

Flow Reactor ◽

Aerosol Formation ◽

Secondary Aerosol ◽

Driving Conditions

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Organic peroxy radical chemistry in oxidation flow reactors and environmental chambers and their atmospheric relevance

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-813-2019 ◽

2019 ◽

Vol 19 (2) ◽

pp. 813-834 ◽

Cited By ~ 13

Author(s):

Zhe Peng ◽

Julia Lee-Taylor ◽

John J. Orlando ◽

Geoffrey S. Tyndall ◽

Jose L. Jimenez

Keyword(s):

Flow Reactor ◽

Operating Conditions ◽

Peroxy Radicals ◽

Relative Importance ◽

Atmospheric Conditions ◽

Aerosol Formation ◽

Ambient Conditions ◽

Flow Reactors ◽

Environmental Chambers ◽

Atmospherically Relevant

Abstract. Oxidation flow reactors (OFRs) are a promising complement to environmental chambers for investigating atmospheric oxidation processes and secondary aerosol formation. However, questions have been raised about how representative the chemistry within OFRs is of that in the troposphere. We investigate the fates of organic peroxy radicals (RO2), which play a central role in atmospheric organic chemistry, in OFRs and environmental chambers by chemical kinetic modeling and compare to a variety of ambient conditions to help define a range of atmospherically relevant OFR operating conditions. For most types of RO2, their bimolecular fates in OFRs are mainly RO2+HO2 and RO2+NO, similar to chambers and atmospheric studies. For substituted primary RO2 and acyl RO2, RO2+RO2 can make a significant contribution to the fate of RO2 in OFRs, chambers and the atmosphere, but RO2+RO2 in OFRs is in general somewhat less important than in the atmosphere. At high NO, RO2+NO dominates RO2 fate in OFRs, as in the atmosphere. At a high UV lamp setting in OFRs, RO2+OH can be a major RO2 fate and RO2 isomerization can be negligible for common multifunctional RO2, both of which deviate from common atmospheric conditions. In the OFR254 operation mode (for which OH is generated only from the photolysis of added O3), we cannot identify any conditions that can simultaneously avoid significant organic photolysis at 254 nm and lead to RO2 lifetimes long enough (∼ 10 s) to allow atmospherically relevant RO2 isomerization. In the OFR185 mode (for which OH is generated from reactions initiated by 185 nm photons), high relative humidity, low UV intensity and low precursor concentrations are recommended for the atmospherically relevant gas-phase chemistry of both stable species and RO2. These conditions ensure minor or negligible RO2+OH and a relative importance of RO2 isomerization in RO2 fate in OFRs within ∼×2 of that in the atmosphere. Under these conditions, the photochemical age within OFR185 systems can reach a few equivalent days at most, encompassing the typical ages for maximum secondary organic aerosol (SOA) production. A small increase in OFR temperature may allow the relative importance of RO2 isomerization to approach the ambient values. To study the heterogeneous oxidation of SOA formed under atmospherically relevant OFR conditions, a different UV source with higher intensity is needed after the SOA formation stage, which can be done with another reactor in series. Finally, we recommend evaluating the atmospheric relevance of RO2 chemistry by always reporting measured and/or estimated OH, HO2, NO, NO2 and OH reactivity (or at least precursor composition and concentration) in all chamber and flow reactor experiments. An easy-to-use RO2 fate estimator program is included with this paper to facilitate the investigation of this topic in future studies.

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Supplementary material to "A New Oxidation Flow Reactor for Measuring Secondary Aerosol Formation of Rapidly Changing Emission Sources"

10.5194/amt-2016-300-supplement ◽

2016 ◽

Author(s):

Pauli Simonen ◽

Erkka Saukko ◽

Panu Karjalainen ◽

Hilkka Timonen ◽

Matthew Bloss ◽

...

Keyword(s):

Flow Reactor ◽

Emission Sources ◽

Aerosol Formation ◽

Secondary Aerosol ◽

Supplementary Material

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Influence of fuel ethanol content on primary emissions and secondary aerosol formation potential for a modern flex-fuel gasoline vehicle

10.5194/acp-2016-579 ◽

2016 ◽

Cited By ~ 1

Author(s):

Hilkka Timonen ◽

Panu Karjalainen ◽

Erkka Saukko ◽

Sanna Saarikoski ◽

Päivi Aakko-Saksa ◽

...

Keyword(s):

Particulate Matter ◽

Organic Compounds ◽

Fuel Ethanol ◽

Aerosol Formation ◽

Secondary Aerosol ◽

Formation Potential ◽

Aerosol Mass ◽

Ethanol Content ◽

Flex Fuel ◽

Primary Emissions

Abstract. The effect of fuel ethanol content (10 %, 85 %, 100 %) on primary emissions and on subsequent secondary aerosol formation was investigated for a EURO5 flex-fuel gasoline vehicle. Emissions were characterized during the New European Driving Cycle (NEDC) using a comprehensive setup of high time resolution instruments. Detailed chemical composition of exhaust particulate matter (PM) was studied using a soot particle aerosol mass spectrometer (SP-AMS) and secondary aerosol formation using a potential aerosol mass (PAM) chamber. For the primary gaseous compounds, an increase in total hydrocarbon emissions and a decrease of aromatic BTEX (benzene, toluene, ethylbenzene and xylenes) compounds was observed when the amount of ethanol in fuel increased. In regard to particles, largest primary particulate matter concentrations and potential to form secondary particles were measured for the E10 fuel (10 % ethanol). As the ethanol content of the fuel increased, a significant decrease in average primary particulate matter concentrations over the NEDC cycle was found, PM emissions being 0.45, 0.25 and 0.15 mg m−3 for E10, E85 and E100, respectively. Similarly, a clear decrease in secondary aerosol formation potential was observed with larger contribution of ethanol in fuel. Secondary to primary PM ratios were 13.4, and 1.5 for E10 and E85, respectively. For E100 a slight decrease in PM mass was observed after the PAM chamber, indicating that the PM produced by secondary aerosol formation was less than the PM lost via e.g. wall losses or degradation of POA in the chamber. For all fuel blends, the formed secondary aerosol consisted mostly of organic compounds. For E10 the contribution of organic compounds containing oxygen increased from 35 %, measured for primary organics, to 62 % after the PAM chamber. For E85 the contribution of organic compounds containing oxygen increased from 42 % (primary) to 57 % (after the PAM chamber), whereas for E100 the amount of oxidized organics remained the same (approximately 62 %) with the PAM chamber when compared to the primary emissions.

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Comparison of secondary organic aerosol formed with an aerosol flow reactor and environmental reaction chambers: effect of oxidant concentration, exposure time and seed particles on chemical composition and yield

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-30575-2014 ◽

2014 ◽

Vol 14 (22) ◽

pp. 30575-30609 ◽

Cited By ~ 1

Author(s):

A. T. Lambe ◽

P. S. Chhabra ◽

T. B. Onasch ◽

W. H. Brune ◽

J. F. Hunter ◽

...

Keyword(s):

Chemical Composition ◽

Gas Phase ◽

Flow Reactor ◽

Heterogeneous Oxidation ◽

Flow Reactors ◽

Seed Particles ◽

Aerosol Mass ◽

Reaction Chambers ◽

Environmental Chambers ◽

Intercomparison Study

Abstract. We performed a systematic intercomparison study of the chemistry and yields of SOA generated from OH oxidation of a common set of gas-phase precursors in a Potential Aerosol Mass (PAM) continuous flow reactor and several environmental chambers. In the flow reactor, SOA precursors were oxidized using OH concentrations ranging from 2.0×108 to 2.2&times1010 molec cm−3 over exposure times of 100 s. In the environmental chambers, precursors were oxidized using OH concentrations ranging from 2×106 to 2×107 molec cm−3 over exposure times of several hours. The OH concentration in the chamber experiments is close to that found in the atmosphere, but the integrated OH exposure in the flow reactor can simulate atmospheric exposure times of multiple days compared to chamber exposure times of only a day or so. A linear correlation analysis of the mass spectra (m=0.91–0.92, r2=0.93–0.94) and carbon oxidation state (m=1.1, r2=0.58) of SOA produced in the flow reactor and environmental chambers for OH exposures of approximately 1011 molec cm−3 s suggests that the composition of SOA produced in the flow reactor and chambers is the same within experimental accuracy as measured with an aerosol mass spectrometer. This similarity in turn suggests that both in the flow reactor and in chambers, SOA chemical composition at low OH exposure is governed primarily by gas-phase OH oxidation of the precursors, rather than heterogeneous oxidation of the condensed particles. In general, SOA yields measured in the flow reactor are lower than measured in chambers for the range of equivalent OH exposures that can be measured in both the flow reactor and chambers. The influence of sulfate seed particles on isoprene SOA yield measurements was examined in the flow reactor. The studies show that seed particles increase the yield of SOA produced in flow reactors by a factor of 3 to 5 and may also account in part for higher SOA yields obtained in the chambers, where seed particles are routinely used.

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Rate constant and secondary organic aerosol formation from the gas-phase reaction of eugenol with hydroxyl radicals

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-2001-2019 ◽

2019 ◽

Vol 19 (3) ◽

pp. 2001-2013 ◽

Cited By ~ 9

Author(s):

Changgeng Liu ◽

Yongchun Liu ◽

Tianzeng Chen ◽

Jun Liu ◽

Hong He

Keyword(s):

Rate Constant ◽

Flow Reactor ◽

Secondary Organic Aerosol ◽

Relative Rate ◽

Organic Aerosol ◽

Organic Nitrates ◽

Phase Reaction ◽

Aerosol Formation ◽

Product Model ◽

Formation Potential

Abstract. Methoxyphenols are an important organic component of wood-burning emissions and considered to be potential precursors of secondary organic aerosol (SOA). In this work, the rate constant and SOA formation potential for the OH-initiated reaction of 4-allyl-2-methoxyphenol (eugenol) were investigated for the first time in an oxidation flow reactor (OFR). The rate constant was 8.01±0.40×10-11 cm3 molecule−1 s−1, determined by the relative rate method. The SOA yield first increased and then decreased as a function of OH exposure and was also dependent on eugenol concentration. The maximum SOA yields (0.11–0.31) obtained at different eugenol concentrations could be expressed well by a one-product model. The carbon oxidation state (OSC) increased linearly and significantly as OH exposure rose, indicating that a high oxidation degree was achieved for SOA. In addition, the presence of SO2 (0–198 ppbv) and NO2 (0–109 ppbv) was conducive to increasing SOA yield, for which the maximum enhancement values were 38.6 % and 19.2 %, respectively. The N∕C ratio (0.032–0.043) indicated that NO2 participated in the OH-initiated reaction, subsequently forming organic nitrates. The results could be helpful for further understanding the SOA formation potential from the atmospheric oxidation of methoxyphenols and the atmospheric aging process of smoke plumes from biomass burning emissions.

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Degradation Kinetics and Secondary Organic Aerosol Formation from Eugenol by Hydroxyl Radicals

10.5194/acp-2018-749 ◽

2018 ◽

Author(s):

Changgeng Liu ◽

Yongchun Liu ◽

Tianzeng Chen ◽

Jun Liu ◽

Hong He

Keyword(s):

Rate Constant ◽

Flow Reactor ◽

Degradation Kinetics ◽

Relative Rate ◽

Organic Nitrates ◽

Aerosol Formation ◽

Product Model ◽

Maximum Enhancement ◽

Formation Potential ◽

Atmospheric Aging

Abstract. Methoxyphenols are an important organic component of wood-burning emissions and considered to be potential precursors of secondary organic aerosols (SOA). In this work, the rate constant and SOA formation potential for the OH-initiated reaction of 4-allyl-2-methoxyphenol (eugenol) were investigated for the first time in an oxidation flow reactor (OFR). The rate constant was (8.01 ± 0.40) × 10−11 cm3 molecule−1 s−1 as determined by the relative rate method. The SOA yield first increased and then decreased as a function of OH exposure, and was also dependent on eugenol concentration. The maximum SOA yields (0.11–0.31) obtained at different eugenol concentrations could be expressed well by an one-product model. The carbon oxidation state (OSC) increased linearly and significantly as OH exposure rose, indicating that a high oxidation degree was achieved for SOA. In addition, the presence of SO2 (0–198 ppbv) and NO2 (0–109 ppbv) was conducive to increasing SOA yield, for which the maximum enhancement values were 38.57 % and 19.17 %, respectively. The N / C ratio (0.032–0.043) indicated that NO2 participated in the OH-initiated reaction, subsequently forming organic nitrates. The results could be helpful for further understanding the SOA formation potential from the atmospheric oxidation of methoxyphenols and the atmospheric aging process of smoke plumes from biomass-burning emissions.

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