On the volatility and production mechanisms of newly formed nitrate and water soluble organic aerosol in Mexico City

Hennigan, Christopher J.; Sullivan, A. P.; Fountoukis, C.; Nenes, Athanasios; Hecobian, A.; Vargas, O.; Hanks, A. T. Case; Huey, L. G.; Lefer, B. L.; Russell, Armistead G.; Weber, R. J.

doi:10.5194/acpd-8-4811-2008

Cited by 33 publications

(49 citation statements)

References 30 publications

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“…[17] These results are consistent with our previous findings that suggest a link between aerosol water and both WSOC p and secondary nitrate production [Hennigan et al, 2008]. In that study, the formation of relatively fresh ($2-3 hours) WSOC p in a region of predominantly anthropogenic emissions was also likely related to aerosol water, as was nitrate, in agreement with known nitrate thermodynamic properties.…”

Section: Resultssupporting

confidence: 82%

Enhanced secondary organic aerosol formation due to water uptake by fine particles

Hennigan

Bergin

Dibb

et al. 2008

Geophysical Research Letters

196

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[1] This study characterizes the partitioning behavior of a significant fraction of the ambient organic aerosol through simultaneous measurements of gas and particle watersoluble organic carbon (WSOC). During the summer in Atlanta, WSOC gas/particle partitioning showed a strong RH dependence that was attributed to particulate liquid water. At elevated RH levels (>$70%), a significant increase in WSOC partitioning to the particle phase was observed and followed the predicted water uptake by fine particles. The enhancement in particle-phase partitioning translated to increased median particle WSOC concentrations ranging from 0.3 -0.9 mg C m À3 . The results provide a detailed overview of the WSOC partitioning behavior in the summertime in an urban region dominated by biogenic emissions, and indicate that secondary organic aerosol formation involving partitioning to liquid water may be a significant aerosol formation route that is generally not considered. Citation: Hennigan, C. J., M. H. Bergin, J. E. Dibb, and R. J. Weber (2008), Enhanced secondary organic aerosol formation due to water uptake by fine particles, Geophys. Res. Lett., 35, L18801,

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Section: Resultssupporting

confidence: 82%

Enhanced secondary organic aerosol formation due to water uptake by fine particles

Hennigan

Bergin

Dibb

et al. 2008

Geophysical Research Letters

196

180

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“…Assuming a particle diameter of 1 µm, the timescale for thermodynamic equilibrium of semi-volatile species was found to be 27±19 min for HNO 3 , 14±11 min for NH 3 , 18±15 min for NO 3 and 15±13 min for NH 4 , on average with a maximum during the night and early morning hours. These timescales are consistent with high-resolution measurements of aerosol nitrate (Hennigan et al, 2008), and with the observation that most of the PM 2.5 mass is in the submicron range . Changes in RH and temperature tend to affect equilibration over longer timescales than changes in aerosol precursor concentration.…”

Section: Discussionsupporting

confidence: 73%

“…3a, b) during the measurement period of 21-30 March (27±19 min for HNO 3 , 14±11 min for NH 3 , 18±15 min for NO 3 and 15±13 min for NH 4 , on average). These values are consistent with the detailed calculations of Wexler and Seinfeld (1992), more recent literature (Meng and Seinfeld, 1996;Dassios and Pandis, 1999;Cruz et al, 2000) and the high resolution measurements of nitrate by Hennigan et al (2008), which shows that measured nitrate lags about 30 min with respect to predictions based on bulk equilibrium. Furthermore, the equilibration timescale for NH 3 is close to that of NH 4 , and, the timescale of HNO 3 is close to that of NO 3 , despite that they include independent measurements of aerosol and gas-phase precursors; this strongly suggests consistency in the timescale analysis.…”

Section: Equilibrium Timescalesupporting

confidence: 79%

Thermodynamic characterization of Mexico City aerosol during MILAGRO 2006

et al. 2009

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Abstract. Fast measurements of aerosol and gas-phase constituents coupled with the ISORROPIA-II thermodynamic equilibrium model are used to study the partitioning of semivolatile inorganic species and phase state of Mexico City aerosol sampled at the T1 site during the MILAGRO 2006 campaign. Overall, predicted semivolatile partitioning agrees well with measurements. PM 2.5 is insensitive to changes in ammonia but is to acidic semivolatile species. For particle sizes up to 1µm diameter, semi-volatile partitioning requires 15-30 min to equilibrate; longer time is typically required during the night and early morning hours. Aerosol and gas-phase speciation always exhibits substantial temporal variability, so that aerosol composition measurements (bulk or size-resolved) obtained over large integration periods are not reflective of its true state. When the aerosol sulfate-to-nitrate molar ratio is less than unity, predictions improve substantially if the aerosol is assumed to follow the deliquescent phase diagram. Treating crustal species as "equivalent sodium" (rather than explicitly) in the thermodynamic equilibrium calculations introduces important biases in predicted aerosol water uptake, nitrate and ammonium; neglecting crustals further increases errors dramatiCorrespondence to: A. Nenes (athanasios.nenes@gatech.edu) cally. This suggests that explicitly considering crustals in the thermodynamic calculations is required to accurately predict the partitioning and phase state of aerosols.

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“…However, during the latter half of the daylight hours, the CCN-active fraction for all particle sizes approaches 100 %. κ CCNc for all particle sizes reaches a maximum within 1-2 h of local noon, suggesting that photochemical processes are dominant at that time, which is consistent with the peak in oxygenated organic aerosol mass (Aiken et al, 2009) and water soluble organic carbon mass (Hennigan et al, 2008) observed during the daytime at the T0 and T1 sites, respectively. New particle formation (NPF) events occurred frequently during MIRAGE 2006(Smith et al, 2008, as illustrated by the particle size distributions (Fig.…”

Section: Diurnal Changes In Aerosol Hygroscopicitysupporting

confidence: 61%

Aerosol mixing state, hygroscopic growth and cloud activation efficiency during MIRAGE 2006

et al. 2013

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Observations of aerosol hygroscopic growth and CCN activation spectra for submicron particles are reported for the T1 ground site outside of Mexico City during the MIRAGE 2006 campaign. κ-Köhler theory is used to evaluate the characteristic hygroscopicity parameter, κ*, for the CCN active aerosol population using both size-resolved HTMDA and size-resolved CCNc measurements. Organic mass fractions (f_org) are evaluated from size-resolved aerosol mass spectrometer (AMS) measurements, from which predictions of the hygroscopicity parameter are compared against κ*.

Strong diurnal changes in aerosol water uptake parameters and aerosol composition are observed. We find that new particle formation (NPF) events are correlated with an increased κ* and CCN-active fraction during the daytime, with greater impact on smaller particles. During NPF events, the number concentration of 40 nm particles acting as CCN at 0.51% ± 0.06% supersaturation can surpass by more than a factor of two the corresponding concentrations of 100 nm particles. We also find that at 06:00–08:00 LT throughout the campaign, fresh traffic emissions result in substantial changes to the chemical distribution of the aerosol, with on average 65% externally mixed fraction for 40 nm particles and 30% externally mixed fraction for 100 nm particles, whereas at midday nearly all particles of both sizes can be described as "internally mixed".

Average activation spectra and growth factor distributions are analyzed for different time periods characterizing the daytime (with and without NPF events), the early morning "rush hour" and the entire campaign. We show that κ* derived from CCNc measurements decreases as a function of size during all time periods, while the CCN-active fraction increases as a function of size. Size-resolved AMS measurements do not predict the observed trend for κ* versus particle size, which can be attributed to unresolved mixing state and the presence of refractory material not measured by the AMS. Measured κ* typically ranges from 0.2 to 0.35, and organics typically make up 60–85 % of the aerosol mass in the size range studied. We show that κ_AMS is able to describe CCN concentrations reasonably well, provided mixing-state information is available, especially at the highest CCN concentrations. This is consistent with other CCN studies carried out in urban environments, and is partly due to the fact that the highest CCN concentrations occur during the daytime when the aerosol is internally mixed. During the early morning rush hour, however, failing to account for the aerosol mixing state results in systematic overestimation of CCN concentrations by as much as 50–100% on average

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On the volatility and production mechanisms of newly formed nitrate and water soluble organic aerosol in Mexico City

Cited by 33 publications

References 30 publications

Enhanced secondary organic aerosol formation due to water uptake by fine particles

Enhanced secondary organic aerosol formation due to water uptake by fine particles

Thermodynamic characterization of Mexico City aerosol during MILAGRO 2006

Aerosol mixing state, hygroscopic growth and cloud activation efficiency during MIRAGE 2006

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