Evolving mass spectra of the oxidized component of organic aerosol: results from aerosol mass spectrometer analyses of aged diesel emissions

Abstract. The species and chemistry responsible for secondary organic aerosol (SOA) formation remain highly uncertain. Laboratory studies of the oxidation of individual, high-flux SOA precursors do not lead to particles with mass spectra (MS) matching those of ambient aged organic material. Additionally, the complexity of real organic particles challenges efforts to identify their chemical origins. We have previously hypothesized that SOA can form from the atmospheric oxidation of a large suite of precursors with varying vapor pressures. Here, we support this hypothesis by using an aerosol mass spectrometer to track the chemical evolution of diesel exhaust as it is photochemically oxidized in an environmental chamber. With explicit knowledge of the condensed-phase MS of the primary emissions from our engine, we are able to decompose each recorded MS into contributing primary and secondary spectra throughout the experiment. We find that the SOA becomes increasingly oxidized as a function of time, quickly approaching a final MS that closely resembles that of ambient aged organic particulate matter. This observation is consistent with our hypothesis of an evolving suite of SOA precursors. Low vapor pressure, semi-volatile organic emissions can form condensable products with even a single generation of oxidation, resulting in an early-arising, relatively less-oxidized SOA. Continued gas-phase oxidation can form highly oxidized SOA in surprisingly young air masses via reaction mechanisms that can add multiple oxygen atoms per generation and result in products with sustained or increased reactivity toward OH.

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Evolving mass spectra of the oxidized component of organic aerosol: results from aerosol mass spectrometer analyses of aged diesel emissions

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-7-10065-2007 ◽

2007 ◽

Vol 7 (4) ◽

pp. 10065-10096 ◽

Cited By ~ 4

Author(s):

A. M. Sage ◽

E. A. Weitkamp ◽

A. L. Robinson ◽

N. M. Donahue

Keyword(s):

Mass Spectrometer ◽

Mass Spectra ◽

Explicit Knowledge ◽

Organic Aerosol ◽

Diesel Emissions ◽

Vapor Pressures ◽

Aerosol Mass Spectrometer ◽

Aerosol Mass ◽

Lower Vapor Pressure ◽

Organic Particles

Abstract. The species and chemistry responsible for secondary organic aerosol (SOA) formation remain highly uncertain. Laboratory studies of the oxidation of individual, high-flux SOA precursors do not lead to particles with mass spectra (MS) matching those of ambient aged organic material. And, the complexity of real organic particles challenges efforts to identify their chemical origins. We have previously hypothesized that SOA can form from the atmospheric oxidation of a large suite of precursors with varying vapor pressures. Here, we support this hypothesis by using an aerosol mass spectrometer to track the chemical evolution of diesel exhaust as it is photochemically oxidized in an environmental chamber. With explicit knowledge of the condensed-phase MS of the primary emissions from our engine, we are able to decompose each recorded MS into contributing primary and secondary spectra throughout the experiment. We find that the SOA MS becomes increasingly oxidized as a function of time, eventually reaching a final MS that closely resembles that of ambient aged organic particulate matter. This observation is consistent with the idea that lower vapor pressure, semi-volatile organic emissions can form condensable products with fewer generations of oxidation, and therefore, they form relatively less oxidized SOA very quickly.

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Investigations of primary and secondary particulate matter of different wood combustion appliances with a high-resolution time-of-flight aerosol mass spectrometer

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-5945-2011 ◽

2011 ◽

Vol 11 (12) ◽

pp. 5945-5957 ◽

Cited By ~ 167

Author(s):

M. F. Heringa ◽

P. F. DeCarlo ◽

R. Chirico ◽

T. Tritscher ◽

J. Dommen ◽

...

Keyword(s):

High Resolution ◽

Mass Spectrometer ◽

Organic Aerosol ◽

Smog Chamber ◽

Resolution Time ◽

Aerosol Mass Spectrometer ◽

Aerosol Mass ◽

Wood Burning ◽

Primary Emissions ◽

Stable Burning

Abstract. A series of photo-oxidation smog chamber experiments were performed to investigate the primary emissions and secondary aerosol formation from two different log wood burners and a residential pellet burner under different burning conditions: starting and flaming phase. Emissions were sampled from the chimney and injected into the smog chamber leading to primary organic aerosol (POA) concentrations comparable to ambient levels. The composition of the aerosol was measured by an Aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS) and black carbon (BC) instrumentation. The primary emissions were then exposed to xenon light to initiate photo-chemistry and subsequent secondary organic aerosol (SOA) production. After correcting for wall losses, the average increase in organic matter (OM) concentrations by SOA formation for the starting and flaming phase experiments with the two log wood burners was found to be a factor of 4.1±1.4 after five hours of aging. No SOA formation was observed for the stable burning phase of the pellet burner. The startup emissions of the pellet burner showed an increase in OM concentration by a factor of 3.3. Including the measured SOA formation potential, average emission factors of BC+POA+SOA, calculated from CO2 emission, were found to be in the range of 0.04 to 3.9 g/kg wood for the stable burning pellet burner and an old log wood burner during startup respectively. SOA contributed significantly to the ion C2H4O2+ at mass to charge ratio m/z 60, a commonly used marker for primary emissions of wood burning. This contribution at m/z 60 can overcompensate for the degradation of levoglucosan leading to an overestimation of the contribution of wood burning or biomass burning to the total OM. The primary organic emissions from the three different burners showed a wide range in O:C atomic ratio (0.19−0.60) for the starting and flaming conditions, which also increased during aging. Primary wood burning emissions have a rather low relative contribution at m/z 43 (f 43) to the total organic mass spectrum. The non-oxidized fragment C3H7+ has a considerable contribution at m/z 43 for the fresh OA with an increasing contribution of the oxygenated ion C2H3O+ during aging. After five hours of aging, the OA has a rather low C2H3O+ signal for a given CO2+ fraction, possibly indicating a higher ratio of acid to non-acid oxygenated compounds in wood burning OA compared to other oxygenated organic aerosol (OOA).

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Factor analysis of combined organic and inorganic aerosol mass spectra from high resolution aerosol mass spectrometer measurements

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-8537-2012 ◽

2012 ◽

Vol 12 (18) ◽

pp. 8537-8551 ◽

Cited By ~ 67

Author(s):

Y. L. Sun ◽

Q. Zhang ◽

J. J. Schwab ◽

T. Yang ◽

N. L. Ng ◽

...

Keyword(s):

High Resolution ◽

Ammonium Nitrate ◽

Mass Spectrometer ◽

Mass Spectra ◽

Organic Aerosol ◽

Organic Nitrates ◽

Spectral Matrix ◽

Aerosol Mass Spectrometer ◽

Aerosol Mass ◽

Inorganic Species

Abstract. Positive matrix factorization (PMF) was applied to the merged high resolution mass spectra of organic and inorganic aerosols from aerosol mass spectrometer (AMS) measurements to investigate the sources and evolution processes of submicron aerosols in New York City in summer 2009. This new approach is able to study the distribution of organic and inorganic species in different types of aerosols, the acidity of organic aerosol (OA) factors, and the fragment ion patterns related to photochemical processing. In this study, PMF analysis of the unified AMS spectral matrix resolved 8 factors. The hydrocarbon-like OA (HOA) and cooking OA (COA) factors contain negligible amounts of inorganic species. The two factors that are primarily ammonium sulfate (SO4-OA) and ammonium nitrate (NO3-OA), respectively, are overall neutralized. Among all OA factors the organic fraction of SO4-OA shows the highest degree of oxidation (O/C = 0.69). Two semi-volatile oxygenated OA (OOA) factors, i.e., a less oxidized (LO-OOA) and a more oxidized (MO-OOA), were also identified. MO-OOA represents local photochemical products with a diurnal profile exhibiting a pronounced noon peak, consistent with those of formaldehyde (HCHO) and Ox(= O3 + NO2). The NO+/NO2+ ion ratio in MO-OOA is much higher than that in NO3-OA and in pure ammonium nitrate, indicating the formation of organic nitrates. The nitrogen-enriched OA (NOA) factor contains ~25% of acidic inorganic salts, suggesting the formation of secondary OA via acid-base reactions of amines. The size distributions of OA factors derived from the size-resolved mass spectra show distinct diurnal evolving behaviors but overall a progressing evolution from smaller to larger particle mode as the oxidation degree of OA increases. Our results demonstrate that PMF analysis of the unified aerosol mass spectral matrix which contains both inorganic and organic aerosol signals may enable the deconvolution of more OA factors and gain more insights into the sources, processes, and chemical characteristics of OA in the atmosphere.

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Laboratory investigation of photochemical oxidation of organic aerosol from wood fires 2: analysis of aerosol mass spectrometer data

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-2227-2009 ◽

2009 ◽

Vol 9 (6) ◽

pp. 2227-2240 ◽

Cited By ~ 151

Author(s):

A. P. Grieshop ◽

N. M. Donahue ◽

A. L. Robinson

Keyword(s):

Source Apportionment ◽

Mass Spectrometer ◽

Mass Spectra ◽

Motor Vehicle ◽

Organic Aerosol ◽

Photochemical Oxidation ◽

Wood Smoke ◽

Aerosol Mass Spectrometer ◽

Aerosol Mass ◽

Spectrometer Data

Abstract. Experiments were conducted to investigate the effects of photo-oxidation on organic aerosol (OA) in dilute wood smoke by exposing emissions from soft- and hard-wood fires to UV light in a smog chamber. This paper focuses on changes in OA composition measured using a unit-mass-resolution quadrupole Aerosol Mass Spectrometer (AMS). The results highlight how photochemical processing can lead to considerable evolution of the mass, volatility and level of oxygenation of biomass-burning OA. Photochemical oxidation produced substantial new OA, more than doubling the OA mass after a few hours of aging under typical summertime conditions. Aging also decreased the volatility of the OA and made it progressively more oxygenated. The results also illustrate strengths of, and challenges with, using AMS data for source apportionment analysis. For example, the mass spectra of fresh and aged BBOA are distinct from fresh motor-vehicle emissions. The mass spectra of the secondary OA produced from aging wood smoke are very similar to those of the oxygenated OA (OOA) that dominates ambient AMS datasets, further reinforcing the connection between OOA and OA formed from photo-chemistry. In addition, aged wood smoke spectra are similar to those from OA created by photo-oxidizing dilute diesel exhaust. This demonstrates that the OOA observed in the atmosphere can be produced by photochemical aging of dilute emissions from different types of combustion systems operating on fuels with modern or fossil carbon. Since OOA is frequently the dominant component of ambient OA, the similarity of spectra of aged emissions from different sources represents an important challenge for AMS-based source apportionment studies.

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Laboratory investigation of photochemical oxidation of organic aerosol from wood fires – Part 2: Analysis of aerosol mass spectrometer data

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-17095-2008 ◽

2008 ◽

Vol 8 (5) ◽

pp. 17095-17130 ◽

Cited By ~ 6

Author(s):

A. P. Grieshop ◽

N. M. Donahue ◽

A. L. Robinson

Keyword(s):

Mass Spectrometer ◽

Biomass Burning ◽

Explicit Knowledge ◽

Uv Light ◽

Organic Aerosol ◽

Photochemical Oxidation ◽

Wood Smoke ◽

Aerosol Mass Spectrometer ◽

Aerosol Mass ◽

Spectrometer Data

Abstract. Experiments were conducted to investigate the effects of photo-oxidation on organic aerosol (OA) in dilute wood smoke by exposing emissions from soft- and hard-wood fires to UV light in a smog chamber. This paper focuses on changes in OA composition measured using a unit mass resolution quadrupole Aerosol Mass Spectrometer (AMS). The results highlight how photochemical processing can lead to considerable evolution of the mass, the volatility and the level of oxygenation of biomass-burning OA. Photochemical oxidation produced substantial new OA, more than doubling the primary contribution after a few hours of aging under typical summertime conditions. Aging decreased the OA volatility of the total OA as measured with a thermodenuder; it also made the OA progressively more oxygenated in every experiment. With explicit knowledge of the condensed-phase mass spectrum (MS) of the primary emissions from each fire, each MS can be decomposed into primary and residual spectra throughout the experiment. The residual spectra provide an estimate of the composition of the photochemically produced OA. These spectra are also very similar to those of the oxygenated OA that dominates ambient AMS datasets. In addition, aged wood smoke spectra are shown to be similar to those from OA created by photo-oxidized dilute diesel exhaust and aged biomass-burning OA measured in urban and remote locations. This demonstrates that the oxygenated OA observed in the atmosphere can be produced by photochemical aging of dilute emissions from combustion of fuels containing both modern and fossil carbon.

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Investigations of primary and secondary particulate matter of different wood combustion appliances with a high-resolution time-of-flight aerosol mass spectrometer

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-11-8081-2011 ◽

2011 ◽

Vol 11 (3) ◽

pp. 8081-8113 ◽

Cited By ~ 6

Author(s):

M. F. Heringa ◽

P. F. DeCarlo ◽

R. Chirico ◽

T. Tritscher ◽

J. Dommen ◽

...

Keyword(s):

High Resolution ◽

Mass Spectrometer ◽

Organic Aerosol ◽

Smog Chamber ◽

Resolution Time ◽

Aerosol Mass Spectrometer ◽

Aerosol Mass ◽

Wood Burning ◽

Primary Emissions ◽

Stable Burning

Abstract. A series of photo-oxidation smog chamber experiments were performed to investigate the primary emissions and secondary aerosol formation from two different log wood burners and a residential pellet burner under different burning conditions: starting and flaming phase. Emissions were sampled from the chimney and injected into the smog chamber leading to primary organic aerosol (POA) concentrations comparable to ambient levels. The composition of the aerosol was measured by an Aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS) and black carbon (BC) instrumentation. The primary emissions were then exposed to xenon light to initiate photo-chemistry and subsequent secondary organic aerosol (SOA) production. After correcting for wall losses, the average increase in organic matter (OM) concentrations by SOA formation for the starting and flaming phase experiments with the two logwood burners was found to be a factor of 4.1 ± 1.4 after five hours of aging. No SOA formation was observed for the stable burning phase of the pellet burner. The startup emissions of the pellet burner showed an increase in OM concentration by a factor of 3.3. Average emission factors of BC + POA + SOA, calculated from CO2 emission, were found to be in the range of 0.04 to 3.9 g kg−1 wood for the stable burning pellet burner and an old log wood burner during startup respectively. SOA contributed significantly to the ion C2H4O2+ at mass to charge ratio m/z 60, a commonly used marker for primary emissions of wood burning. The primary organic emissions from the three different burners showed a wide range in O/C atomic ratio (0.19–0.60) for the starting and flaming conditions, which also increased during aging. Primary wood burning emissions have a rather low relative contribution at m/z 43 (f43) to the total organic mass spectrum. The non-oxidized fragment C3H7+ has a considerable contribution at m/z 43 for the fresh OA with an increasing contribution of the oxygenated ion C2H3O+ during aging. After five hours of aging, the OA has a rather low C2H3O+ signal for a given CO2+ fraction, possibly indicating a higher ratio of acid to non-acid oxygenated compounds in wood burning OA compared to other OOA.

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Secondary organic aerosol formation from reaction of tertiary amines with nitrate radical

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-16585-2008 ◽

2008 ◽

Vol 8 (4) ◽

pp. 16585-16608 ◽

Cited By ~ 6

Author(s):

M. E. Erupe ◽

D. J. Price ◽

P. J. Silva ◽

Q. G. J. Malloy ◽

L. Qi ◽

...

Keyword(s):

Mass Spectrometer ◽

Secondary Organic Aerosol ◽

Organic Aerosol ◽

Nitrate Radical ◽

Tertiary Amines ◽

Aerosol Formation ◽

Night Time ◽

Aerosol Mass Spectrometer ◽

Aerosol Mass ◽

Secondary Organic Aerosol Formation

Abstract. Secondary organic aerosol formation from the reaction of tertiary amines with nitrate radical was investigated in an indoor environmental chamber. Particle chemistry was monitored using a high resolution aerosol mass spectrometer while gas-phase species were detected using a proton transfer reaction mass spectrometer. Trimethylamine, triethylamine and tributylamine were studied. Results indicate that tributylamine forms the most aerosol mass followed by trimethylamine and triethylamine respectively. Spectra from the aerosol mass spectrometer indicate the formation of complex non-salt aerosol products. We propose a reaction mechanism that proceeds via abstraction of a proton by nitrate radical followed by RO2 chemistry. Rearrangement of the aminyl alkoxy radical through hydrogen shift leads to the formation of hydroxylated amides, which explain most of the higher mass ions in the mass spectra. These experiments show that oxidation of tertiary amines by nitrate radical may be an important night-time source of secondary organic aerosol.

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Characterization of a real-time tracer for isoprene epoxydiols-derived secondary organic aerosol (IEPOX-SOA) from aerosol mass spectrometer measurements

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-11807-2015 ◽

2015 ◽

Vol 15 (20) ◽

pp. 11807-11833 ◽

Cited By ~ 121

Author(s):

W. W. Hu ◽

P. Campuzano-Jost ◽

B. B. Palm ◽

D. A. Day ◽

A. M. Ortega ◽

...

Keyword(s):

Mass Spectrometer ◽

Secondary Organic Aerosol ◽

Transport Model ◽

Organic Aerosol ◽

Oxidation Products ◽

Chemical Transport Model ◽

Aerosol Mass Spectrometer ◽

Aerosol Mass ◽

Multiple Field

Abstract. Substantial amounts of secondary organic aerosol (SOA) can be formed from isoprene epoxydiols (IEPOX), which are oxidation products of isoprene mainly under low-NO conditions. Total IEPOX-SOA, which may include SOA formed from other parallel isoprene oxidation pathways, was quantified by applying positive matrix factorization (PMF) to aerosol mass spectrometer (AMS) measurements. The IEPOX-SOA fractions of organic aerosol (OA) in multiple field studies across several continents are summarized here and show consistent patterns with the concentration of gas-phase IEPOX simulated by the GEOS-Chem chemical transport model. During the Southern Oxidant and Aerosol Study (SOAS), 78 % of PMF-resolved IEPOX-SOA is accounted by the measured IEPOX-SOA molecular tracers (2-methyltetrols, C5-Triols, and IEPOX-derived organosulfate and its dimers), making it the highest level of molecular identification of an ambient SOA component to our knowledge. An enhanced signal at C5H6O+ (m/z 82) is found in PMF-resolved IEPOX-SOA spectra. To investigate the suitability of this ion as a tracer for IEPOX-SOA, we examine fC5H6O (fC5H6O= C5H6O+/OA) across multiple field, chamber, and source data sets. A background of ~ 1.7 ± 0.1 ‰ (‰ = parts per thousand) is observed in studies strongly influenced by urban, biomass-burning, and other anthropogenic primary organic aerosol (POA). Higher background values of 3.1 ± 0.6 ‰ are found in studies strongly influenced by monoterpene emissions. The average laboratory monoterpene SOA value (5.5 ± 2.0 ‰) is 4 times lower than the average for IEPOX-SOA (22 ± 7 ‰), which leaves some room to separate both contributions to OA. Locations strongly influenced by isoprene emissions under low-NO levels had higher fC5H6O (~ 6.5 ± 2.2 ‰ on average) than other sites, consistent with the expected IEPOX-SOA formation in those studies. fC5H6O in IEPOX-SOA is always elevated (12–40 ‰) but varies substantially between locations, which is shown to reflect large variations in its detailed molecular composition. The low fC5H6O (< 3 ‰) reported in non-IEPOX-derived isoprene-SOA from chamber studies indicates that this tracer ion is specifically enhanced from IEPOX-SOA, and is not a tracer for all SOA from isoprene. We introduce a graphical diagnostic to study the presence and aging of IEPOX-SOA as a triangle plot of fCO2 vs. fC5H6O. Finally, we develop a simplified method to estimate ambient IEPOX-SOA mass concentrations, which is shown to perform well compared to the full PMF method. The uncertainty of the tracer method is up to a factor of ~ 2, if the fC5H6O of the local IEPOX-SOA is not available. When only unit mass-resolution data are available, as with the aerosol chemical speciation monitor (ACSM), all methods may perform less well because of increased interferences from other ions at m/z 82. This study clarifies the strengths and limitations of the different AMS methods for detection of IEPOX-SOA and will enable improved characterization of this OA component.

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Single-particle measurements of bouncing particles and in situ collection efficiency from an airborne aerosol mass spectrometer (AMS) with light-scattering detection

Atmospheric Measurement Techniques ◽

10.5194/amt-10-3801-2017 ◽

2017 ◽

Vol 10 (10) ◽

pp. 3801-3820 ◽

Cited By ~ 6

Author(s):

Jin Liao ◽

Charles A. Brock ◽

Daniel M. Murphy ◽

Donna T. Sueper ◽

André Welti ◽

...

Keyword(s):

Light Scattering ◽

Mass Spectrometer ◽

Single Particle ◽

Total Mass ◽

Mass Spectra ◽

Collection Efficiency ◽

Aerosol Mass Spectrometer ◽

Mass Spectral ◽

Aerosol Mass ◽

Spectral Signal

Abstract. A light-scattering module was coupled to an airborne, compact time-of-flight aerosol mass spectrometer (LS-AMS) to investigate collection efficiency (CE) while obtaining nonrefractory aerosol chemical composition measurements during the Southeast Nexus (SENEX) campaign. In this instrument, particles scatter light from an internal laser beam and trigger saving individual particle mass spectra. Nearly all of the single-particle data with mass spectra that were triggered by scattered light signals were from particles larger than ∼ 280 nm in vacuum aerodynamic diameter. Over 33 000 particles are characterized as either prompt (27 %), delayed (15 %), or null (58 %), according to the time and intensity of their total mass spectral signals. The particle mass from single-particle spectra is proportional to that derived from the light-scattering diameter (dva-LS) but not to that from the particle time-of-flight (PToF) diameter (dva-MS) from the time of the maximum mass spectral signal. The total mass spectral signal from delayed particles was about 80 % of that from prompt ones for the same dva-LS. Both field and laboratory data indicate that the relative intensities of various ions in the prompt spectra show more fragmentation compared to the delayed spectra. The particles with a delayed mass spectral signal likely bounced off the vaporizer and vaporized later on another surface within the confines of the ionization source. Because delayed particles are detected by the mass spectrometer later than expected from their dva-LS size, they can affect the interpretation of particle size (PToF) mass distributions, especially at larger sizes. The CE, measured by the average number or mass fractions of particles optically detected that had measurable mass spectra, varied significantly (0.2–0.9) in different air masses. The measured CE agreed well with a previous parameterization when CE > 0.5 for acidic particles but was sometimes lower than the minimum parameterized CE of 0.5.

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