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

Simonen, Pauli; Saukko, Erkka; Karjalainen, Panu; Timonen, Hilkka; Bloss, Matthew; Aakko-Saksa, Päivi; Rönkkö, Topi; Keskinen, Jorma; Maso, Miikka Dal

doi:10.5194/amt-10-1519-2017

Cited by 58 publications

(54 citation statements)

References 43 publications

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“…It is known from model simulations and experimental studies that the O 3 oxidation of PAHs and organic molecules with C=C double bonds require an activation energy of 40 to 80 kJ mol −1 (Berkemeier et al, 2016;Lee et al, 2009;Pöschl et al, 2001;Stephens et al, 1989). Even though many different compounds can be found on soot surfaces, PAHs are considered to be a good reference compound (Slowik et al, 2004). A temperature change by 5 K would change the reaction speed and therefore t act by a factor of 2.…”

Section: Discussionmentioning

confidence: 99%

Impact of isolated atmospheric aging processes on the cloud condensation nuclei activation of soot particles

et al. 2019

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Abstract. The largest contributors to the uncertainty in assessing the anthropogenic contribution in radiative forcing are the direct and indirect effects of aerosol particles on the Earth's radiative budget. Soot particles are of special interest since their properties can change significantly due to aging processes once they are emitted into the atmosphere. Probably the largest obstacle for the investigation of these processes in the laboratory is the long atmospheric lifetime of 1 week, requiring tailored experiments that cover this time span. This work presents results on the ability of two types of soot, obtained using a miniCAST soot generator, to act as cloud condensation nuclei (CCN) after exposure to atmospherically relevant levels of ozone (O3) and humidity. Aging times of up to 12 h were achieved by successful application of the continuous-flow stirred tank reactor (CSTR) concept while allowing for size selection of particles prior to the aging step. Particles of 100 nm diameter and rich in organic carbon (OC) that were initially CCN inactive showed significant CCN activity at supersaturations (SS) down to 0.3 % after 10 h of exposure to 200 ppb of O3. While this process was not affected by different levels of relative humidity in the range of 5 %–75 %, a high sensitivity towards the ambient/reaction temperature was observed. Soot particles with a lower OC content required an approximately 4-fold longer aging duration to show CCN activity at the same SS. Prior to the slow change in the CCN activity, a rapid increase in the particle diameter was detected which occurred within several minutes. This study highlights the applicability of the CSTR approach for the simulation of atmospheric aging processes, as aging durations beyond 12 h can be achieved in comparably small aerosol chamber volumes (<3 m3). Implementation of our measurement results in a global aerosol-climate model, ECHAM6.3-HAM2.3, showed a statistically significant increase in the regional and global CCN burden and cloud droplet number concentration.

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Section: Discussionmentioning

confidence: 99%

Impact of isolated atmospheric aging processes on the cloud condensation nuclei activation of soot particles

et al. 2019

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“…In that stage, the oxidation products of precursors have condensed into the particle phase and formed secondary aerosol. However, because the oxidant concentrations are unrealistically high in PAM, the UV-light intensity used is non-tropospheric and the residence times are much shorter than in the atmosphere (e.g., Simonen et al, 2017), precursor oxidation products also have other possible fates; they can be oxidized too far and form non-condensable oxidation products before condensation (accelerated chemistry) and they can exit the reactor before the condensation occurs. Also, precursor oxidation products can be lost on the PAM walls although the losses on the walls are minimized by the chamber design (Lambe et al, 2011).…”

Section: Pam Artifacts and Lossesmentioning

confidence: 99%

Comparison of primary and secondary particle formation from natural gas engine exhaust and of their volatility characteristics

et al. 2017

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Abstract. Natural gas usage in the traffic and energy production sectors is a growing trend worldwide; thus, an assessment of its effects on air quality, human health and climate is required. Engine exhaust is a source of primary particulate emissions and secondary aerosol precursors, which both contribute to air quality and can cause adverse health effects. Technologies, such as cleaner engines or fuels, that produce less primary and secondary aerosols could potentially significantly decrease atmospheric particle concentrations and their adverse effects. In this study, we used a potential aerosol mass (PAM) chamber to investigate the secondary aerosol formation potential of natural gas engine exhaust. The PAM chamber was used with a constant UV-light voltage, which resulted in relatively long equivalent atmospheric ages of 11 days at most. The studied retro-fitted natural gas engine exhaust was observed to form secondary aerosol. The mass of the total aged particles, i.e., particle mass measured downstream of the PAM chamber, was 6-268 times as high as the mass of the emitted primary exhaust particles. The secondary organic aerosol (SOA) formation potential was measured to be 9-20 mg kg −1 fuel . The total aged particles mainly consisted of organic matter, nitrate, sulfate and ammonium, with the fractions depending on exhaust after-treatment and the engine parameters used. Also, the volatility, composition and concentration of the total aged particles were found to depend on the engine operating mode, catalyst temperature and catalyst type. For example, a high catalyst temperature promoted the formation of sulfate particles, whereas a low catalyst temperature promoted nitrate formation. However, in particular, the concentration of nitrate needed a long time to stabilize -more than half an hour -which complicated the conclusions but also indicates the sensitivity of nitrate measurements on experimental parameters such as emission source and system temperatures. Sulfate was measured to have the highest evaporation temperature, and nitrate had the lowest. The evaporation temperature of ammonium depended on the fractions of nitrate and sulfate in the particles. The average volatility of the total aged particles was measured to be lower than that of primary particles, indicating better stability of the aged natural gas engine-emitted aerosol in the atmosphere. According to the results of this study, the exhaust of a natural gas engine equipped with a catalyst forms secondary aerosol when the atmospheric ages in a PAM chamber are several days long. The secondary aerosol matter has different physical characteristics from those of primary particulate emissions.

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“…The former study reported evidence for the incorporation of nitrogen into SOA. OFRs have also been increasingly employed to process emissions of vehicles, biomass burning, and other combustion sources (Table 1) in which NO can often be hundreds of ppm Martinsson et al, 2015;Karjalainen et al, 2016;Link et al, 2016;Schill et al, 2016;Alanen et al, 2017;Simonen et al, 2017). It can be expected that such a high NO input together with very high VOC concentrations would cause a substantial deviation from the good OFR operation conditions identified in Peng et al (2016).…”

Section: Introductionmentioning

confidence: 99%

Modeling of the chemistry in oxidation flow reactors with high initial NO

Peng

Jimenez

2017

Atmos. Chem. Phys.

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Abstract. Oxidation flow reactors (OFRs) are increasingly employed in atmospheric chemistry research because of their high efficiency of OH radical production from low-pressure Hg lamp emissions at both 185 and 254 nm (OFR185) or 254 nm only (OFR254). OFRs have been thought to be limited to studying low-NO chemistry (in which peroxy radicals (RO 2 ) react preferentially with HO 2 ) because NO is very rapidly oxidized by the high concentrations of O 3 , HO 2 , and OH in OFRs. However, many groups are performing experiments by aging combustion exhaust with high NO levels or adding NO in the hopes of simulating high-NO chemistry (in which RO 2 + NO dominates). This work systematically explores the chemistry in OFRs with high initial NO. Using box modeling, we investigate the interconversion of Ncontaining species and the uncertainties due to kinetic parameters. Simple initial injection of NO in OFR185 can result in more RO 2 reacted with NO than with HO 2 and minor non-tropospheric photolysis, but only under a very narrow set of conditions (high water mixing ratio, low UV intensity, low external OH reactivity (OHR ext ), and initial NO concentration (NO in ) of tens to hundreds of ppb) that account for a very small fraction of the input parameter space. These conditions are generally far away from experimental conditions of published OFR studies with high initial NO. In particular, studies of aerosol formation from vehicle emissions in OFRs often used OHR ext and NO in several orders of magnitude higher. Due to extremely high OHR ext and NO in , some studies may have resulted in substantial non-tropospheric photolysis, strong delay to RO 2 chemistry due to peroxynitrate formation, VOC reactions with NO 3 dominating over those with OH, and faster reactions of OH-aromatic adducts with NO 2 than those with O 2 , all of which are irrelevant to ambient VOC photooxidation chemistry. Some of the negative effects are the worst for alkene and aromatic precursors. To avoid undesired chemistry, vehicle emissions generally need to be diluted by a factor of > 100 before being injected into an OFR. However, sufficiently diluted vehicle emissions generally do not lead to high-NO chemistry in OFRs but are rather dominated by the low-NO RO 2 + HO 2 pathway. To ensure high-NO conditions without substantial atmospherically irrelevant chemistry in a more controlled fashion, new techniques are needed.

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

Cited by 58 publications

References 43 publications

Impact of isolated atmospheric aging processes on the cloud condensation nuclei activation of soot particles

Impact of isolated atmospheric aging processes on the cloud condensation nuclei activation of soot particles

Comparison of primary and secondary particle formation from natural gas engine exhaust and of their volatility characteristics

Modeling of the chemistry in oxidation flow reactors with high initial NO

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