OH, HO₂, and RO₂ radical chemistry in a rural forest environment: measurements, model comparisons, and evidence of a missing radical sink

Atmospheric chemistry and physics, Journal Year: 2023, Volume and Issue: 23(18), P. 10287 - 10311

Published: Sept. 15, 2023

Abstract. The hydroxyl (OH), hydroperoxy (HO2), and organic peroxy (RO2) radicals play important roles in atmospheric chemistry. In the presence of nitrogen oxides (NOx), reactions between OH volatile compounds (VOCs) can initiate a radical propagation cycle that leads to production ozone secondary aerosols. Previous measurements these under low-NOx conditions forested environments characterized by emissions biogenic VOCs, including isoprene monoterpenes, have shown discrepancies with modeled concentrations. During summer 2016, OH, HO2, RO2 concentrations were measured as part Program for Research on Oxidants: Photochemistry, Emissions, Transport – Atmospheric Measurements Oxidants Summer (PROPHET-AMOS) campaign midlatitude deciduous broadleaf forest. HO2 made laser-induced fluorescence–fluorescence assay gas expansion (LIF-FAGE) techniques, total (XO2) mixing ratios Ethane CHemical AMPlifier (ECHAMP) instrument. Supporting photolysis frequencies, NOx, O3, meteorological data used constrain zero-dimensional box model utilizing either Regional Chemical Mechanism (RACM2) or Master (MCM). Model simulations tested influence HOx regeneration within oxidation scheme from Leuven Isoprene (LIM1). On average, LIM1 models overestimated daytime maximum approximately 40 % 65 more than factor 2 XO2. Modeled XO2 also significantly higher at night. Addition + accretion terpene-derived partially explain discrepancy night but cannot when reactivity is dominated isoprene. isoprene-derived hydroxyhydroperoxides (ISOPOOH) 10 during daytime, consistent overestimation Constraining concentration improves agreement ISOPOOH concentrations, suggesting are These results suggest may be missing an sink could overestimating rate product formation this

Language: Английский

---

The important contribution of secondary formation and biomass burning to oxidized organic nitrogen (OON) in a polluted urban area: insights from in situ measurements of a chemical ionization mass spectrometer (CIMS)

Atmospheric chemistry and physics, Journal Year: 2023, Volume and Issue: 23(15), P. 8855 - 8877

Published: Aug. 9, 2023

Abstract. To investigate the sources and formation mechanism of oxidized organic nitrogen (OON), field measurements OON were conducted using an iodide-adduct chemical ionization mass spectrometer equipped with a Filter Inlet for Gases AEROsols (FIGAERO-CIMS) during fall 2018 in megacity Guangzhou, China. Using levoglucosan as tracer biomass burning emissions, results show that (49±23 %) secondary (51±23 accounted comparable fractions to total particle-phase (pOON) but 24±25 % 76±25 gas-phase (gOON), respectively, signifying important contribution pOON gOON this urban area. Calculations production rates indicated hydroxyl radical (42 nitrate (NO3) (49 oxidation pathways potentially dominated gOON. A high concentration NO3 radicals afternoon was observed, demonstrating daytime might be more than previous recognition. Monoterpenes, found major precursors gOON, mainly from anthropogenic emissions The ratio Ox ([Ox] = [O3] + [NO2]) increased function relative humidity aerosol surface area, indicating heterogeneous reaction pathway pOON. Finally, highly 6 11 oxygen atoms highlighting complex processes ambient air. Overall, our improve understanding dynamic variation atmosphere.

Language: Английский

---

Comparison of isoprene chemical mechanisms under atmospheric night-time conditions in chamber experiments: evidence of hydroperoxy aldehydes and epoxy products from NO₃ oxidation

Atmospheric chemistry and physics, Journal Year: 2023, Volume and Issue: 23(5), P. 3147 - 3180

Published: March 10, 2023

Abstract. The gas-phase reaction of isoprene with the nitrate radical (NO3) was investigated in experiments outdoor SAPHIR chamber under atmospherically relevant conditions specifically respect to chemical lifetime and fate nitrato-organic peroxy radicals (RO2). Observations organic products were compared concentrations expected from different mechanisms: (1) Master Chemical Mechanism, which simplifies NO3 chemistry by only considering one RO2 isomer; (2) mechanism derived Caltech chamber, considers isomers; (3) FZJ-NO3 quantum calculations, addition includes equilibrium reactions isomers, unimolecular epoxidation alkoxy radicals. Measurements using mass spectrometer instruments give evidence that new pathways predicted calculations play a role oxidation isoprene. Hydroperoxy aldehyde (HPALD) species, are specific RO2, detected even presence an OH scavenger, excluding possibility concurrent hydroxyl (OH) is responsible for their formation. In addition, ion signals at masses can be attributed epoxy compounds, radicals, detected. methyl vinyl ketone (MVK) methacrolein (MACR) confirm decomposition implemented cannot compete ring-closure calculations. validity further supported good agreement between measured simulated reactivity. Nevertheless, needs investigations absolute importance Absolute nitrates such as hydroperoxides would required experimentally determine product yields branching ratios but could not due lack calibration standards these compounds. temporal evolution traces species hydroperoxides, carbonyl alcohols well hydroperoxy aldehydes observed demonstrates ozone atmospheric small on timescale night (12 h) typical oxidant concentrations. However, present potentially also produced contribute nocturnal loss.

Language: Английский

---

Online Calibration of a Chemical Ionization Mass Spectrometer for Multifunctional Biogenic Organic Nitrates

ACS ES&T Air, Journal Year: 2024, Volume and Issue: 1(9), P. 1066 - 1083

Published: Aug. 8, 2024

Multifunctional organic nitrates derived from biogenic volatile compounds are important for understanding ozone and secondary aerosol production oxidation reactions in the presence of nitrogen oxides. Their measurement is challenging, part because quantification these difficult time consuming due to techniques required synthesize purify authentic standards. We describe a novel online synthesis separation technique demonstrate its use calibration chemical ionization mass spectrometer using iodide reagent ions (I– CIMS) measure four isomers isoprene hydroxy nitrate (IHN; C5H9NO4), two methyl vinyl ketone (MVKHN; C4H7NO5), monoterpene (MTHN; C10H17NO4). further apply our an + NO3 HO2 reactor calibrate six hydroperoxide (C5H9NO5). find large range detection sensitivities ion molecule (IMR) temperature dependencies among reported analytes measured as (I–) clusters. report wide normalized (normalized Hz pptv–1; nHz pptv–1) by [I·H2O]− signal this class (0.2–82 pptv–1). The (4,3)-MVKHN isomer exceptional high sensitivity with chemistry (82 ± 5 pptv–1), which can lead inaccurate representation budget if moderate assumed. I– CIMS demonstrates much smaller IHNs (10–34 most abundant having similar ((1,2): 24 3 (4,3): 30 4 These calibrations reveal significantly different distribution than would be determined assuming uniform measurements at ground site Pasadena, CA, during summer 2021. A comparison another calibrated (using CF3O– ions) select showed good agreement IHN MVKHN.

Language: Английский

---

Characterization and Seasonal Variation of PM_2.5 Composition in Xi’an, Northwest China: Oxygenated and Nitrogenous Organic Aerosol

ACS Earth and Space Chemistry, Journal Year: 2024, Volume and Issue: 8(7), P. 1370 - 1384

Published: June 20, 2024

Oxygenated (CHO) and nitrogenous (CHON) organic aerosols (OA) are important components of fine particulate matter (PM2.5) in urban environments. To achieve a molecular-level understanding the seasonal variation OA fraction, ambient PM2.5 samples collected from April 2018 to March 2019 Xi'an, Northwest China, were analyzed using an iodide Chemical Ionization Mass Spectrometer combined with Filter Inlet for Gases AEROsols (FIGAERO–CIMS). The set compounds identified by FIGAERO–CIMS was estimated represent 28.6% PM2.5. Evaporation temperatures measured indicated that semivolatile (SVOCs) dominant among analytes. Concentrations CHO (6.01 ± 4.24 μg m–3) CHON (3.17 2.34 increased winter, especially during severe haze episode January 2019. comprised up 75.3 3.2% total detected compounds. average carbon oxidation state (OSC¯) slightly elevated summer samples. mainly nitro-aromatics their abundance substantially which attributed extensive biomass burning demonstrated high levels levoglucosan. Biomass-burning related sources accounted 61.0 19.6% 68.3 21.9% concentration autumn respectively, while secondary formation source species spring (70.1 11.6%) (79.8 7.0%). These results emphasize importance as reveal clear need control used heating Xi'an its surroundings.

Language: Английский

---

Source apportionment of gaseous Nitrophenols and their contribution to HONO formation in an urban area

Chemosphere, Journal Year: 2023, Volume and Issue: 338, P. 139499 - 139499

Published: July 17, 2023

Language: Английский

---

Measuring Biogenic Volatile Organic Compounds from Leaves Exposed to Submicron Black Carbon Using Portable Sensor

Pollutants, Journal Year: 2024, Volume and Issue: 4(2), P. 187 - 195

Published: April 3, 2024

Biogenic volatile organic compounds (BVOCs) are responsible for the formation of ozone and secondary aerosols (SOAs). Our knowledge about how black carbon particles influence BVOC emissions from terrestrial ecosystems is limited; vegetation captures as a sink. In this research, leaves four plants were measured using an RAE PGM-7300 analyzer. Then, types trees exposed to submicron 24 h 48 in ambient environment, respectively. Comparisons between before after exposure performed. results indicated that varied 90 270 μg g−1 h−1 depended on species. The had negligible impacts trees.

Language: Английский

---

Summertime Ozone Production at Carlsbad Caverns National Park, New Mexico: Influence of Oil and Natural Gas Development

Journal of Geophysical Research Atmospheres, Journal Year: 2024, Volume and Issue: 129(14)

Published: July 16, 2024

Abstract Southeastern New Mexico's Carlsbad Caverns National Park (CAVE) has increasingly experienced summertime ozone (O 3 ) exceeding an 8‐hr average of 70 parts per billion by volume (ppbv). The park is located in the western part Permian oil and natural gas (O&G) basin, where production rates have increased fivefold last decade. We investigate O –precursor relationships constraining F0AM box model to observations nitrogen oxides (NO x = NO + 2 a suite volatile organic compounds (VOCs) collected at CAVE during summer 2019. O&G‐related VOCs dominated calculated VOC reactivity with hydroxyl radicals (OH) on days when concentrations were primarily controlled local photochemistry. Radical budget analysis showed that levels high enough impose sensitivity morning hours, while subsequent loss through photochemical consumption led ‐sensitive conditions afternoon. Maximum daily was responsive both reductions, reductions proving most effective. underestimated observed 5‐day episode influenced photochemically aged O&G emissions, as indicated back‐trajectory analysis, low i‐ / n ‐pentane ratios, enhanced secondary VOCs, ratios total reactive oxidized y ). Model‐observation agreement improved , which approximates time emission, indicating large fraction this formed nonlocally.

Language: Английский

---

Daytime isoprene nitrates under changing NO_x and O₃

Atmospheric chemistry and physics, Journal Year: 2023, Volume and Issue: 23(14), P. 8473 - 8485

Published: July 31, 2023

Abstract. Organonitrates are important species in the atmosphere due to their impacts on NOx, HOx, and O3 budgets, potential contribute secondary organic aerosol (SOA) mass. This work presents a steady-state modelling approach assess of changes NOx concentrations organonitrates produced from isoprene oxidation. The diverse formation pathways dictate responses different groups NOx. For example, predominantly formed OH-initiated oxidation favour under lower-ozone moderate-NOx concentrations, whereas via daytime NO3 show highest high-O3 with little dependence concentrations. Investigating response total reveals complex nonlinear behaviour implications that could inform expectations organonitrate as efforts made reduce including region NOx–O3 space where concentration is relatively insensitive O3. These conclusions further contextualised by estimating volatility revealing for high low-volatility high-ozone conditions.

Language: Английский

---

The Important Contribution of Secondary Formation and Biomass Burning to Oxidized Organic Nitrogen (OON) in a Polluted Urban Area: Insights from In Situ FIGAERO-CIMS Measurements

Published: Jan. 16, 2023

Abstract. To investigate the sources and formation mechanism of oxidized organic nitrogen (OON), field measurements OON were conducted using an iodide-adduct chemical ionization mass spectrometer equipped with a Filter Inlet for Gases AEROsols (FIGAERO-CIMS) during fall 2018 in megacity Guangzhou, China. Using levoglucosan as tracer biomass burning emissions, results show that (49 %) secondary (51 accounted comparable fractions to total particle-phase (pOON), while 24 % 76 gas-phase (gOON), respectively, signifying important contribution pOON gOON this urban area. Calculations production rates nitrates (gON) indicated hydroxyl radical (42 nitrate (NO3) oxidation pathways potentially dominated gON. High concentration NO3 afternoon daytime was observed, demonstrating might be more than previous recognition. Monoterpenes, found major precursor gON, mainly from anthropogenic emissions The ratio Ox ([Ox] = [O3] + [NO2]) increased function relative humidity aerosol surface area, indicating heterogeneous reaction pathway pOON. Finally, highly 6 11 oxygen atoms highlighting complex processes ambient air. Overall, our can improve understanding dynamic variation atmosphere.

Language: Английский

---