Modeling Photosensitized Secondary Organic Aerosol Formation in Laboratory and Ambient Aerosols

Tsui, William G.; Rao, Yi; Dai, Hai‐Lung; McNeill, V. Faye

doi:10.1021/acs.est.7b01416

Cited by 36 publications

(47 citation statements)

References 36 publications

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“…In GAMMA 5.0, these equations represent the temporal evolution of aqueous species in both aerosol and cloudwater and mass transfer of gas phase species to and from aerosol and cloudwater. More detailed information regarding GAMMA, including Henry's constants used and equations calculating uptake of gas-phase species, can be found in previous work using older versions of GAMMA [21,46]. For transitions between cloudwater and aqueous aerosols, a unitless scaling factor, f w , is calculated as the ratio of the liquid water fraction in cloudwater to the liquid water fraction in aqueous aerosol, in order to adjust aqueous phase concentrations based on the differences in the amount of liquid water available.…”

Section: Methodsmentioning

confidence: 99%

Impact of Aerosol-Cloud Cycling on Aqueous Secondary Organic Aerosol Formation

2019

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Chemical processing of organic material in aqueous atmospheric aerosols and cloudwater is known to form secondary organic aerosols (SOA), although the extent to which each of these processes contributes to total aerosol mass is unclear. In this study, we use GAMMA 5.0, a photochemical box model with coupled gas and aqueous-phase chemistry, to consider the impact of aqueous organic reactions in both aqueous aerosols and clouds on isoprene epoxydiol (IEPOX) SOA over a range of pH for both aqueous phases, including cycling between cloud and aerosol within a single simulation. Low pH aqueous aerosol, in the absence of organic coatings or other morphology which may limit uptake of IEPOX, is found to be an efficient source of IEPOX SOA, consistent with previous work. Cloudwater at pH 4 or lower is also found to be a potentially significant source of IEPOX SOA. This phenomenon is primarily attributed to the relatively high uptake of IEPOX to clouds as a result of higher water content in clouds as compared with aerosol. For more acidic cloudwater, the aqueous organic material is comprised primarily of IEPOX SOA and lower-volatility organic acids. Both cloudwater pH and the time of day or sequence of aerosol-to-cloud or cloud-to-aerosol transitions impacted final aqueous SOA mass and composition in the simulations. The potential significance of cloud processing as a contributor to IEPOX SOA production could account for discrepancies between predicted IEPOX SOA mass from atmospheric models and measured ambient IEPOX SOA mass, or observations of IEPOX SOA in locations where mass transfer limitations are expected in aerosol particles.

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Section: Methodsmentioning

confidence: 99%

Impact of Aerosol-Cloud Cycling on Aqueous Secondary Organic Aerosol Formation

2019

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“…There is evidence that triplet-forming, light-absorbing species, e.g., imidazoles and pyrazines, are formed in drops and particles (De Haan et al, 2009Hawkins et al, 2018), and a few laboratory studies have examined how illuminated imidazole particles can oxidize isoprene or other alkenes to increase PM mass (Aregahegn et al, 2013;Rossignol et al, 2014). But the formation of SOA(aq) from such reactions appears not to be significant under environmentally relevant conditions where concentrations of triplet precursors are much lower (Tsui et al, 2017). While we recently made the first measurements of triplet concentrations in fog waters (Kaur and Anastasio, 2018b), there are no measurements of 3 C * in particles, making it difficult to assess their significance.…”

Section: Introductionmentioning

confidence: 99%

Photooxidants from brown carbon and other chromophores in illuminated particle extracts

et al. 2019

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Abstract. While photooxidants are important in atmospheric condensed phases, there are very few measurements in particulate matter (PM). Here we measure light absorption and the concentrations of three photooxidants – hydroxyl radical (⚫OH), singlet molecular oxygen (1O2*), and oxidizing triplet excited states of organic matter (3C*) – in illuminated aqueous extracts of wintertime particles from Davis, California. 1O2* and 3C*, which are formed from photoexcitation of brown carbon (BrC), have not been previously measured in PM. In the extracts, mass absorption coefficients for dissolved organic compounds (MACDOC) at 300 nm range between 13 000 and 30 000 cm2 (g C)−1 are approximately twice as high as previous values in Davis fogs. The average (±1σ)⚫OH steady-state concentration in particle extracts is 4.4(±2.3)×10-16 M, which is very similar to previous values in fog, cloud, and rain: although our particle extracts are more concentrated, the resulting enhancement in the rate of ⚫OH photoproduction is essentially canceled out by a corresponding enhancement in concentrations of natural sinks for ⚫OH. In contrast, concentrations of the two oxidants formed primarily from brown carbon (i.e., 1O2* and 3C*) are both enhanced in the particle extracts compared to Davis fogs, a result of higher concentrations of dissolved organic carbon and faster rates of light absorption in the extracts. The average 1O2* concentration in the PM extracts is 1.6(±0.5)×10-12 M, 7 times higher than past fog measurements, while the average concentration of oxidizing triplets is 1.0(±0.4)×10-13 M, nearly double the average Davis fog value. Additionally, the rates of 1O2* and 3C* photoproduction are both well correlated with the rate of sunlight absorption. Since we cannot experimentally measure photooxidants under ambient particle water conditions, we measured the effect of PM dilution on oxidant concentrations and then extrapolated to ambient particle conditions. As the particle mass concentration in the extracts increases, measured concentrations of ⚫OH remain relatively unchanged, 1O2* increases linearly, and 3C* concentrations increase less than linearly, likely due to quenching by dissolved organics. Based on our measurements, and accounting for additional sources and sinks that should be important under PM conditions, we estimate that [⚫OH] in particles is somewhat lower than in dilute cloud/fog drops, while [3C*] is 30 to 2000 times higher in PM than in drops, and [1O2*] is enhanced by a factor of roughly 2400 in PM compared to drops. Because of these enhancements in 1O2* and 3C* concentrations, the lifetimes of some highly soluble organics appear to be much shorter in particle liquid water than under foggy/cloudy conditions. Based on extrapolating our measured rates of formation in PM extracts, BrC-derived singlet molecular oxygen and triplet excited states are overall the dominant sinks for organic compounds in particle liquid water, with an aggregate rate of reaction for each oxidant that is approximately 200–300 times higher than the aggregate rate of reactions for organics with ⚫OH. For individual, highly soluble reactive organic compounds it appears that 1O2* is often the major sink in particle water, which is a new finding. Triplet excited states are likely also important in the fate of individual particulate organics, but assessing this requires additional measurements of triplet interactions with dissolved organic carbon in natural samples.

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“…[21][22][23] Such halogen-containing compounds play an important role in both tropospheric and stratospheric chemistry, destroying ozone through catalytic cycles, influencing hydroxyl radical chemistry, and affecting NOx concentrations. 24 Moreover, they can trigger new particle formation, 25,26 potentially affecting the evolution of cloud condensation nuclei (CCN), 19 and thus, indirectly climate processes. In addition, some of these halogenated products might also be toxic, impacting human health.…”

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confidence: 99%

Real-Time Detection of Gas-Phase Organohalogens from Aqueous Photochemistry Using Orbitrap Mass Spectrometry

Roveretto

Mingchan

Hayeck

et al. 2019

ACS Earth Space Chem.

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Marine short-lived halogenated compounds, emitted from algae, phytoplankton and other marine biota, affect significantly both the troposphere and the stratosphere. Here we show that such compounds might also be photochemically produced through photosensitized reactions in surface water. Gas-phase products were detected and identified by high-resolution mass spectrometry, more particularly by means of an atmospheric pressure chemical ionization (APCI) source coupled to an Orbitrap mass spectrometer. Under simulated solar irradiation, halogenated organic compounds were produced and detected in the gas phase when a proxy of dissolved organic matter, i.e., 4-benzoylbenzoic acid, was excited into its triplet state. We present a mechanism explaining the formation of a variety of such halogenated compounds. These photochemical reactions take place at the air/sea interface and are, therefore, a potential source of short-lived halogenated compounds in the atmosphere, participating in the tropospheric halogen cycle.

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Modeling Photosensitized Secondary Organic Aerosol Formation in Laboratory and Ambient Aerosols

Cited by 36 publications

References 36 publications

Impact of Aerosol-Cloud Cycling on Aqueous Secondary Organic Aerosol Formation

Impact of Aerosol-Cloud Cycling on Aqueous Secondary Organic Aerosol Formation

Photooxidants from brown carbon and other chromophores in illuminated particle extracts

Real-Time Detection of Gas-Phase Organohalogens from Aqueous Photochemistry Using Orbitrap Mass Spectrometry

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