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Article ; Online: Source and variability of formaldehyde (HCHO) at northern high latitudes

T. Zhao / J. Mao / W. R. Simpson / I. De Smedt / L. Zhu / T. F. Hanisco / G. M. Wolfe / J. M. St. Clair / G. González Abad / C. R. Nowlan / B. Barletta / S. Meinardi / D. R. Blake / E. C. Apel / R. S. Hornbrook

Atmospheric Chemistry and Physics, Vol 22, Pp 7163-

an integrated satellite, aircraft, and model study

2022 Volume 7178

Abstract: Here we use satellite observations of formaldehyde (HCHO) vertical column densities (VCD) from the TROPOspheric Monitoring Instrument (TROPOMI), aircraft measurements, combined with a nested regional chemical transport model (GEOS-Chem at

Abstract	Here we use satellite observations of formaldehyde (HCHO) vertical column densities (VCD) from the TROPOspheric Monitoring Instrument (TROPOMI), aircraft measurements, combined with a nested regional chemical transport model (GEOS-Chem at <math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">0.5</mn><mo>×</mo><mn mathvariant="normal">0.625</mn><msup><mi/><mo>∘</mo></msup></mrow></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="60pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="b5bd9fa9b9f716ab33f0bb6532f347fc"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-22-7163-2022-ie00001.svg" width="60pt" height="11pt" src="acp-22-7163-2022-ie00001.png"/></svg:svg> resolution), to better understand the variability and sources of summertime HCHO in Alaska. We first evaluate GEOS-Chem with in-situ airborne measurements during the Atmospheric Tomography Mission 1 (ATom-1) aircraft campaign. We show reasonable agreement between observed and modeled HCHO, isoprene, monoterpenes and the sum of methyl vinyl ketone and methacrolein (MVK + MACR) in the continental boundary layer. In particular, HCHO profiles show spatial homogeneity in Alaska, suggesting a minor contribution of biogenic emissions to HCHO VCD. We further examine the TROPOMI HCHO product in Alaska in summer, reprocessed by GEOS-Chem model output for a priori profiles and shape factors. For years with low wildfire activity (e.g., 2018), we find that HCHO VCDs are largely dominated by background HCHO (58 %–71 %), with minor contributions from wildfires (20 %–32 %) and biogenic VOC emissions (8 %–10 %). For years with intense wildfires (e.g., 2019), summertime HCHO VCD is dominated by wildfire emissions (50 %–72 %), with minor contributions from background (22 %–41 %) and biogenic VOCs (6 %–10 %). In particular, the model ...
Keywords	Physics ; QC1-999 ; Chemistry ; QD1-999
Subject code	551
Language	English
Publishing date	2022-06-01T00:00:00Z
Publisher	Copernicus Publications
Document type	Article ; Online
Database	BASE - Bielefeld Academic Search Engine (life sciences selection)

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Article ; Online: Constraining emissions of volatile organic compounds from western US wildfires with WE-CAN and FIREX-AQ airborne observations

L. Jin / W. Permar / V. Selimovic / D. Ketcherside / R. J. Yokelson / R. S. Hornbrook / E. C. Apel / I.-T. Ku / J. L. Collett Jr. / A. P. Sullivan / D. A. Jaffe / J. R. Pierce / A. Fried / M. M. Coggon / G. I. Gkatzelis / C. Warneke / E. V. Fischer / L. Hu

Atmospheric Chemistry and Physics, Vol 23, Pp 5969-

2023 Volume 5991

Abstract: The impact of biomass burning (BB) on the atmospheric burden of volatile organic compounds (VOCs) is highly uncertain. Here we apply the GEOS-Chem chemical transport model (CTM) to constrain BB emissions in the western USA at ∼ 25 km resolution. Across ... ...

Abstract	The impact of biomass burning (BB) on the atmospheric burden of volatile organic compounds (VOCs) is highly uncertain. Here we apply the GEOS-Chem chemical transport model (CTM) to constrain BB emissions in the western USA at ∼ 25 km resolution. Across three BB emission inventories widely used in CTMs, the inventory–inventory comparison suggests that the totals of 14 modeled BB VOC emissions in the western USA agree with each other within 30 %–40 %. However, emissions for individual VOCs can differ by a factor of 1–5, driven by the regionally averaged emission ratios (ERs, reflecting both assigned ERs for specific biome and vegetation classifications) across the three inventories. We further evaluate GEOS-Chem simulations with aircraft observations made during WE-CAN (Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption and Nitrogen) and FIREX-AQ (Fire Influence on Regional to Global Environments and Air Quality) field campaigns. Despite being driven by different global BB inventories or applying various injection height assumptions, the model–observation comparison suggests that GEOS-Chem simulations underpredict observed vertical profiles by a factor of 3–7. The model shows small to no bias for most species in low-/no-smoke conditions. We thus attribute the negative model biases mostly to underestimated BB emissions in these inventories. Tripling BB emissions in the model reproduces observed vertical profiles for primary compounds, i.e., CO , propane, benzene, and toluene. However, it shows no to less significant improvements for oxygenated VOCs, particularly for formaldehyde, formic acid, acetic acid, and lumped ≥ C 3 aldehydes, suggesting the model is missing secondary sources of these compounds in BB-impacted environments. The underestimation of primary BB emissions in inventories is likely attributable to underpredicted amounts of effective dry matter burned, rather than errors in fire detection, injection height, or ERs, as constrained by aircraft and ground measurements. We cannot rule out ...
Keywords	Physics ; QC1-999 ; Chemistry ; QD1-999
Subject code	550 ; 551
Language	English
Publishing date	2023-05-01T00:00:00Z
Publisher	Copernicus Publications
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Article ; Online: Composition and reactivity of volatile organic compounds in the South Coast Air Basin and San Joaquin Valley of California

S. Liu / B. Barletta / R. S. Hornbrook / A. Fried / J. Peischl / S. Meinardi / M. Coggon / A. Lamplugh / J. B. Gilman / G. I. Gkatzelis / C. Warneke / E. C. Apel / A. J. Hills / I. Bourgeois / J. Walega / P. Weibring / D. Richter / T. Kuwayama / M. FitzGibbon /

D. Blake

Atmospheric Chemistry and Physics, Vol 22, Pp 10937-

2022 Volume 10954

Abstract: Comprehensive aircraft measurements of volatile organic compounds (VOCs) covering the South Coast Air Basin (SoCAB) and San Joaquin Valley (SJV) of California were obtained in the summer of 2019. Combined with the CO, CH 4 , and NO x data, the total ... ...

Abstract	Comprehensive aircraft measurements of volatile organic compounds (VOCs) covering the South Coast Air Basin (SoCAB) and San Joaquin Valley (SJV) of California were obtained in the summer of 2019. Combined with the CO, CH 4 , and NO x data, the total calculated gas-phase hydroxyl radical reactivity (cOHR TOTAL ) was quantified to be 6.1 and 4.6 s −1 for the SoCAB and SJV, respectively. VOCs accounted for ∼ 60 %–70 % of the cOHR TOTAL in both basins. In particular, oxygenated VOCs (OVOCs) contributed > 60 % of the cOHR of total VOCs (cOHR VOC ) and the total observed VOC mixing ratio. Primary biogenic VOCs (BVOCs) represented a minor fraction ( < 2 %) of the total VOC mixing ratio but accounted for 21 % and 6 % of the cOHR VOC in the SoCAB and SJV, respectively. Furthermore, the contribution of BVOCs to the cOHR VOC increased with increasing cOHR VOC in the SoCAB, suggesting that BVOCs were important ozone precursors during high ozone episodes. Spatially, the trace gases were heterogeneously distributed in the SoCAB, with their mixing ratios and cOHR being significantly greater over the inland regions than the coast, while their levels were more evenly distributed in SJV. The results highlight that a better grasp of the emission rates and sources of OVOCs and BVOCs is essential for a predictive understanding of the ozone abundance and distribution in California.
Keywords	Physics ; QC1-999 ; Chemistry ; QD1-999
Subject code	511
Language	English
Publishing date	2022-08-01T00:00:00Z
Publisher	Copernicus Publications
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Article ; Online: Importance of reactive halogens in the tropical marine atmosphere

A. Badia / C. E. Reeves / A. R. Baker / A. Saiz-Lopez / R. Volkamer / T. K. Koenig / E. C. Apel / R. S. Hornbrook / L. J. Carpenter / S. J. Andrews / T. Sherwen / R. von Glasow

Atmospheric Chemistry and Physics, Vol 19, Pp 3161-

a regional modelling study using WRF-Chem

2019 Volume 3189

Abstract: This study investigates the impact of reactive halogen species (RHS, containing chlorine (Cl), bromine (Br) or iodine (I)) on atmospheric chemistry in the tropical troposphere and explores the sensitivity to uncertainties in the fluxes of RHS to the ... ...

Abstract	This study investigates the impact of reactive halogen species (RHS, containing chlorine (Cl), bromine (Br) or iodine (I)) on atmospheric chemistry in the tropical troposphere and explores the sensitivity to uncertainties in the fluxes of RHS to the atmosphere and their chemical processing. To do this, the regional chemistry transport model WRF-Chem has been extended to include Br and I, as well as Cl chemistry for the first time, including heterogeneous recycling reactions involving sea-salt aerosol and other particles, reactions of Br and Cl with volatile organic compounds (VOCs), along with oceanic emissions of halocarbons, VOCs and inorganic iodine. The study focuses on the tropical east Pacific using field observations from the Tropical Ocean tRoposphere Exchange of Reactive halogen species and Oxygenated VOC (TORERO) campaign (January–February 2012) to evaluate the model performance. Including all the new processes, the model does a reasonable job reproducing the observed mixing ratios of bromine oxide (BrO) and iodine oxide (IO), albeit with some discrepancies, some of which can be attributed to difficulties in the model's ability to reproduce the observed halocarbons. This is somewhat expected given the large uncertainties in the air–sea fluxes of the halocarbons in a region where there are few observations of their seawater concentrations. We see a considerable impact on the inorganic bromine ( Br y ) partitioning when heterogeneous chemistry is included, with a greater proportion of the Br y in active forms such as BrO, HOBr and dihalogens. Including debromination of sea salt increases BrO slightly throughout the free troposphere, but in the tropical marine boundary layer, where the sea-salt particles are plentiful and relatively acidic, debromination leads to overestimation of the observed BrO. However, it should be noted that the modelled BrO was extremely sensitive to the inclusion of reactions between Br and the oxygenated VOCs (OVOCs), which convert Br to HBr, a far less reactive form of Br y . ...
Keywords	Physics ; QC1-999 ; Chemistry ; QD1-999
Subject code	333
Language	English
Publishing date	2019-03-01T00:00:00Z
Publisher	Copernicus Publications
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Article ; Online: Validation of satellite formaldehyde (HCHO) retrievals using observations from 12 aircraft campaigns

L. Zhu / G. González Abad / C. R. Nowlan / C. Chan Miller / K. Chance / E. C. Apel / J. P. DiGangi / A. Fried / T. F. Hanisco / R. S. Hornbrook / L. Hu / J. Kaiser / F. N. Keutsch / W. Permar / J. M. St. Clair / G. M. Wolfe

Atmospheric Chemistry and Physics, Vol 20, Pp 12329-

2020 Volume 12345

Abstract: Formaldehyde (HCHO) has been measured from space for more than 2 decades. Owing to its short atmospheric lifetime, satellite HCHO data are used widely as a proxy of volatile organic compounds (VOCs; please refer to Appendix A for abbreviations and ... ...

Abstract	Formaldehyde (HCHO) has been measured from space for more than 2 decades. Owing to its short atmospheric lifetime, satellite HCHO data are used widely as a proxy of volatile organic compounds (VOCs; please refer to Appendix A for abbreviations and acronyms), providing constraints on underlying emissions and chemistry. However, satellite HCHO products from different satellite sensors using different algorithms have received little validation so far. The accuracy and consistency of HCHO retrievals remain largely unclear. Here we develop a validation platform for satellite HCHO retrievals using in situ observations from 12 aircraft campaigns with a chemical transport model (GEOS-Chem) as the intercomparison method. Application to the NASA operational OMI HCHO product indicates negative biases ( −44.5 % to −21.7 %) under high-HCHO conditions, while it indicates high biases ( +66.1 % to +112.1 %) under low-HCHO conditions. Under both conditions, HCHO a priori vertical profiles are likely not the main driver of the biases. By providing quick assessment of systematic biases in satellite products over large domains, the platform facilitates, in an iterative process, optimization of retrieval settings and the minimization of retrieval biases. It is also complementary to localized validation efforts based on ground observations and aircraft spirals.
Keywords	Physics ; QC1-999 ; Chemistry ; QD1-999
Subject code	551
Language	English
Publishing date	2020-10-01T00:00:00Z
Publisher	Copernicus Publications
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Article ; Online: Novel approaches to improve estimates of short-lived halocarbon emissions during summer from the Southern Ocean using airborne observations

E. Asher / R. S. Hornbrook / B. B. Stephens / D. Kinnison / E. J. Morgan / R. F. Keeling / E. L. Atlas / S. M. Schauffler / S. Tilmes / E. A. Kort / M. S. Hoecker-Martínez / M. C. Long / J.-F. Lamarque / A. Saiz-Lopez / K. McKain / C. Sweeney / A. J. Hills / E. C. Apel

Atmospheric Chemistry and Physics, Vol 19, Pp 14071-

2019 Volume 14090

Abstract: Fluxes of halogenated volatile organic compounds (VOCs) over the Southern Ocean remain poorly understood, and few atmospheric measurements exist to constrain modeled emissions of these compounds. We present observations of CHBr 3 , CH 2 Br 2 , CH 3 I , ... ...

Abstract	Fluxes of halogenated volatile organic compounds (VOCs) over the Southern Ocean remain poorly understood, and few atmospheric measurements exist to constrain modeled emissions of these compounds. We present observations of CHBr 3 , CH 2 Br 2 , CH 3 I , CHClBr 2 , CHBrCl 2 , and CH 3 Br during the O 2 ∕N 2 Ratio and CO 2 Airborne Southern Ocean (ORCAS) study and the second Atmospheric Tomography mission (ATom-2) in January and February of 2016 and 2017. Good model–measurement correlations were obtained between these observations and simulations from the Community Earth System Model (CESM) atmospheric component with chemistry (CAM-Chem) for CHBr 3 , CH 2 Br 2 , CH 3 I , and CHClBr 2 but all showed significant differences in model : measurement ratios. The model : measurement comparison for CH 3 Br was satisfactory and for CHBrCl 2 the low levels present precluded us from making a complete assessment. Thereafter, we demonstrate two novel approaches to estimate halogenated VOC fluxes; the first approach takes advantage of the robust relationships that were found between airborne observations of O 2 and CHBr 3 , CH 2 Br 2 , and CHClBr 2 . We use these linear regressions with O 2 and modeled O 2 distributions to infer a biological flux of halogenated VOCs. The second approach uses the Stochastic Time-Inverted Lagrangian Transport (STILT) particle dispersion model to explore the relationships between observed mixing ratios and the product of the upstream surface influence of sea ice, chl a , absorption due to detritus, and downward shortwave radiation at the surface, which in turn relate to various regional hypothesized sources of halogenated VOCs such as marine phytoplankton, phytoplankton in sea-ice brines, and decomposing organic matter in surface seawater. These relationships can help evaluate the likelihood of particular halogenated VOC sources and in the case of statistically significant correlations, such as was found for CH 3 I , may be used to derive an estimated flux field. Our results are consistent with a ...
Keywords	Physics ; QC1-999 ; Chemistry ; QD1-999
Subject code	511 ; 290
Language	English
Publishing date	2019-11-01T00:00:00Z
Publisher	Copernicus Publications
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Article ; Online: Tropospheric HONO distribution and chemistry in the southeastern US

C. Ye / X. Zhou / D. Pu / J. Stutz / J. Festa / M. Spolaor / C. Tsai / C. Cantrell / R. L. Mauldin III / A. Weinheimer / R. S. Hornbrook / E. C. Apel / A. Guenther / L. Kaser / B. Yuan / T. Karl / J. Haggerty / S. Hall / K. Ullmann /

J. Smith / J. Ortega

Atmospheric Chemistry and Physics, Vol 18, Pp 9107-

2018 Volume 9120

Abstract: Here we report the measurement results of nitrous acid (HONO) and a suite of relevant parameters on the NCAR C-130 research aircraft in the southeastern US during the NOMADSS 2013 summer field study. The daytime HONO concentration ranged from low parts ... ...

Abstract	Here we report the measurement results of nitrous acid (HONO) and a suite of relevant parameters on the NCAR C-130 research aircraft in the southeastern US during the NOMADSS 2013 summer field study. The daytime HONO concentration ranged from low parts per trillion by volume (pptv) in the free troposphere (FT) to mostly within 5–15 pptv in the background planetary boundary layer (PBL). There was no discernible vertical HONO gradient above the lower flight altitude of 300 m in the PBL, and the transport of ground surface HONO was not found to be a significant contributor to the tropospheric HONO budget. The total in situ HONO source mean (±1 SD) was calculated as 53 (±21) pptv h −1 during the day. The upper-limit contribution from NO x -related reactions was 10 (±5) pptv h −1 , and the contribution from photolysis of particulate nitrate ( p NO 3 ) was 38 (±23) pptv h −1 , based on the measured p NO 3 concentrations and the median p NO 3 photolysis rate constant of 2.0 × 10 −4 s −1 determined in the laboratory using ambient aerosol samples. The photolysis of HONO contributed to less than 10 % of the primary OH source. However, a recycling NO x source via p NO 3 photolysis was equivalent to ∼ 2.3 × 10 −6 mol m −2 h −1 in the air column within the PBL, a considerable supplementary NO x source in the low-NO x background area. Up to several tens of parts per trillion by volume of HONO were observed in power plant and urban plumes during the day, mostly produced in situ from precursors including NO x and p NO 3 . Finally, there was no observable accumulation of HONO in the nocturnal residual layer and the nocturnal FT in the background southeastern US, with an increase in the HONO ∕ NO x ratio of ≤ 3 × 10 −4 h −1 after sunset.
Keywords	Physics ; QC1-999 ; Chemistry ; QD1-999
Subject code	333
Language	English
Publishing date	2018-06-01T00:00:00Z
Publisher	Copernicus Publications
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Article ; Online: Formaldehyde evolution in US wildfire plumes during the Fire Influence on Regional to Global Environments and Air Quality experiment (FIREX-AQ)

J. Liao / G. M. Wolfe / R. A. Hannun / J. M. St. Clair / T. F. Hanisco / J. B. Gilman / A. Lamplugh / V. Selimovic / G. S. Diskin / J. B. Nowak / H. S. Halliday / J. P. DiGangi / S. R. Hall / K. Ullmann / C. D. Holmes / C. H. Fite / A. Agastra / T. B. Ryerson / J. Peischl /

I. Bourgeois / C. Warneke / M. M. Coggon / G. I. Gkatzelis / K. Sekimoto / A. Fried / D. Richter / P. Weibring / E. C. Apel / R. S. Hornbrook / S. S. Brown / C. C. Womack / M. A. Robinson / R. A. Washenfelder / P. R. Veres / J. A. Neuman

Atmospheric Chemistry and Physics, Vol 21, Pp 18319-

2021 Volume 18331

Abstract: Formaldehyde (HCHO) is one of the most abundant non-methane volatile organic compounds (VOCs) emitted by fires. HCHO also undergoes chemical production and loss as a fire plume ages, and it can be an important oxidant precursor. In this study, we ... ...

Abstract	Formaldehyde (HCHO) is one of the most abundant non-methane volatile organic compounds (VOCs) emitted by fires. HCHO also undergoes chemical production and loss as a fire plume ages, and it can be an important oxidant precursor. In this study, we disentangle the processes controlling HCHO by examining its evolution in wildfire plumes sampled by the NASA DC-8 during the Fire Influence on Regional to Global Environments and Air Quality experiment (FIREX-AQ) field campaign. In 9 of the 12 analyzed plumes, dilution-normalized HCHO increases with physical age (range 1–6 h ). The balance of HCHO loss (mainly via photolysis) and production (via OH-initiated VOC oxidation) seems to control the sign and magnitude of this trend. Plume-average OH concentrations, calculated from VOC decays, range from − 0.5 ( ± 0.5) × 10 6 to 5.3 ( ± 0.7) × 10 6 cm −3 . The production and loss rates of dilution-normalized HCHO seem to decrease with plume age. Plume-to-plume variability in dilution-normalized secondary HCHO production correlates with OH abundance rather than normalized OH reactivity, suggesting that OH is the main driver of fire-to-fire variability in HCHO secondary production. Analysis suggests an effective HCHO yield of 0.33 ( ± 0.05) per VOC molecule oxidized for the 12 wildfire plumes. This finding can help connect space-based HCHO observations to the oxidizing capacity of the atmosphere and to VOC emissions.
Keywords	Physics ; QC1-999 ; Chemistry ; QD1-999
Language	English
Publishing date	2021-12-01T00:00:00Z
Publisher	Copernicus Publications
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Article ; Online: Heterogeneity and chemical reactivity of the remote troposphere defined by aircraft measurements

H. Guo / C. M. Flynn / M. J. Prather / S. A. Strode / S. D. Steenrod / L. Emmons / F. Lacey / J.-F. Lamarque / A. M. Fiore / G. Correa / L. T. Murray / G. M. Wolfe / J. M. St. Clair / M. Kim / J. Crounse / G. Diskin / J. DiGangi / B. C. Daube / R. Commane /

K. McKain / J. Peischl / T. B. Ryerson / C. Thompson / T. F. Hanisco / D. Blake / N. J. Blake / E. C. Apel / R. S. Hornbrook / J. W. Elkins / E. J. Hintsa / F. L. Moore / S. Wofsy

Atmospheric Chemistry and Physics, Vol 21, Pp 13729-

2021 Volume 13746

Abstract: The NASA Atmospheric Tomography (ATom) mission built a photochemical climatology of air parcels based on in situ measurements with the NASA DC-8 aircraft along objectively planned profiling transects through the middle of the Pacific and Atlantic oceans. ...

Abstract	The NASA Atmospheric Tomography (ATom) mission built a photochemical climatology of air parcels based on in situ measurements with the NASA DC-8 aircraft along objectively planned profiling transects through the middle of the Pacific and Atlantic oceans. In this paper we present and analyze a data set of 10 s (2 km) merged and gap-filled observations of the key reactive species driving the chemical budgets of O 3 and CH 4 (O 3 , CH 4 , CO, H 2 O, HCHO, H 2 O 2 , CH 3 OOH, C 2 H 6 , higher alkanes, alkenes, aromatics, NO x , HNO 3 , HNO 4 , peroxyacetyl nitrate, other organic nitrates), consisting of 146 494 distinct air parcels from ATom deployments 1 through 4. Six models calculated the O 3 and CH 4 photochemical tendencies from this modeling data stream for ATom 1. We find that 80 %–90 % of the total reactivity lies in the top 50 % of the parcels and 25 %–35 % in the top 10 %, supporting previous model-only studies that tropospheric chemistry is driven by a fraction of all the air. In other words, accurate simulation of the least reactive 50 % of the troposphere is unimportant for global budgets. Surprisingly, the probability densities of species and reactivities averaged on a model scale (100 km) differ only slightly from the 2 km ATom data, indicating that much of the heterogeneity in tropospheric chemistry can be captured with current global chemistry models. Comparing the ATom reactivities over the tropical oceans with climatological statistics from six global chemistry models, we find excellent agreement with the loss of O 3 and CH 4 but sharp disagreement with production of O 3 . The models sharply underestimate O 3 production below 4 km in both Pacific and Atlantic basins, and this can be traced to lower NO x levels than observed. Attaching photochemical reactivities to measurements of chemical species allows for a richer, yet more constrained-to-what-matters, set of metrics for model evaluation.
Keywords	Physics ; QC1-999 ; Chemistry ; QD1-999
Subject code	511
Language	English
Publishing date	2021-09-01T00:00:00Z
Publisher	Copernicus Publications
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Article ; Online: Airborne intercomparison of HO x measurements using laser-induced fluorescence and chemical ionization mass spectrometry during ARCTAS

G. Chen / J. R. Olson / J. H. Crawford / E. Kosciuch / R. S. Hornbrook / R. L. Mauldin III / C. A. Cantrell / W. H. Brune / J. Mao / X. Ren / H. B. Singh

Atmospheric Measurement Techniques Discussions, Vol 5, Iss 2, Pp 2529-

2012 Volume 2565

Abstract: The hydroxyl (OH) and hydroperoxyl (HO 2 ) radicals, collectively called HO x , play central roles in tropospheric chemistry. Accurate measurements of OH and HO 2 are critical to examine our understanding of atmospheric chemistry. Intercomparisons of ... ...

Abstract	The hydroxyl (OH) and hydroperoxyl (HO 2 ) radicals, collectively called HO x , play central roles in tropospheric chemistry. Accurate measurements of OH and HO 2 are critical to examine our understanding of atmospheric chemistry. Intercomparisons of different techniques for detecting OH and HO 2 are vital to evaluate their measurement capabilities. Three instruments that measured OH and/or HO 2 radicals were deployed on the NASA DC-8 aircraft throughout Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS), in the spring and summer of 2008. One instrument was the Penn State Airborne Tropospheric Hydrogen Oxides Sensor (ATHOS) for OH and HO 2 measurements based on Laser-Induced Fluorescence (LIF) spectroscopy. A second instrument was the NCAR Selected-Ion Chemical Ionization Mass Spectrometer (SI-CIMS) for OH measurement. A third instrument was the NCAR Peroxy Radical Chemical Ionization Mass Spectrometer (PeRCIMS) for HO 2 measurement. Formal intercomparison of LIF and CIMS was conducted for the first time on a same aircraft platform. The three instruments were calibrated by quantitative photolysis of water vapor by UV light at 184.9 nm with three different calibration systems. The absolute accuracies were ±32% (2σ) for the LIF instrument, ±65% (2σ) for the SI-CIMS instrument, and ±50% (2σ) for the PeRCIMS instrument. In general, good agreement was obtained between the CIMS and LIF measurements of both OH and HO 2 measurements. Linear regression of the entire data set yields [OH] CIMS = 0.89 × [OH] LIF + 2.8 × 10 5 cm −3 with a correlation coefficient, r 2 = 0.72 for OH and [HO 2 ] CIMS = 0.86 × [HO 2 ] LIF + 3.9 parts per trillion by volume (pptv, equivalent to pmol mol −1 ) with a correlation coefficient, r 2 = 0.72 for HO 2 . In general, the difference between CIMS and LIF instruments for OH and HO 2 measurements can be explained by their combined measurement uncertainties. Comparison with box model results shows some similarities for both the CIMS and LIF measurements. First, the observed-to-modeled HO 2 ratio increases greatly for higher NO mixing ratios, indicating that the model may not properly account for HO x sources that correlate with NO. Second, the observed-to-modeled OH ratio increases with increasing isoprene mixing ratios, suggesting either incomplete understanding of isoprene chemistry in the model or interferences in the measurements in environments where biogenic emissions dominate ambient volatile organic compounds.
Keywords	Meteorology. Climatology ; QC851-999 ; Physics ; QC1-999 ; Science ; Q ; DOAJ:Meteorology and Climatology ; DOAJ:Earth and Environmental Sciences ; Engineering (General). Civil engineering (General) ; TA1-2040 ; Earthwork. Foundations ; TA715-787
Subject code	290
Language	English
Publishing date	2012-03-01T00:00:00Z
Publisher	Copernicus Publications
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Kategorien

Inter-library loan at ZB MED

Full text online

More links

Kategorien

Inter-library loan at ZB MED

Full text online

More links

Kategorien

Inter-library loan at ZB MED

Full text online

More links

Kategorien

Inter-library loan at ZB MED

Full text online

More links

Kategorien

Inter-library loan at ZB MED