Composition and reactivity of volatile organic compounds in the South Coast Air Basin and San Joaquin Valley of California
Year: 2022
Type: article
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.
Authors: Shang Liu, Barbara Barletta, Rebecca S. Hornbrook, Alan Fried, Jeff Peischl, Simone Meinardi, Matthew Coggon, Aaron Lamplugh, Jessica B. Gilman, Georgios I. Gkatzelis, Carsten Warneke, Eric C. Apel, Alan J. Hills, Ilann Bourgeois, James Walega, Petter Weibring, Dirk Richter, Toshihiro Kuwayama, Michael FitzGibbon, Donald Blake
Institutions: California Air Resources Board, University of California, Irvine, NSF National Center for Atmospheric Research, NSF NCAR Atmospheric Chemistry Observations & Modeling, Institute of Arctic and Alpine Research, University of Colorado Boulder, Cooperative Institute for Research in Environmental Sciences, NOAA Chemical Sciences Laboratory
Language: English
Subfield: Atmospheric Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,725
Awards: G1335240794, G1350247877, The Management and Operation of the National Center for Atmoshperic Research (NCAR), IN SUPPORT OF THE SCIENCE GOALS OF THE SUMMER 2019 NASA FIRECHEM MISSION WE PROPOSE TO DEPLOY THE TRACE ORGANIC GAS ANALYZER (TOGA) COUPLED TO A HIGH RESOLUTION (HR) TOFWERK TIME-OF-FLIGHT (TOF) MASS SPECTROMETER (FAST GAS CHROMATOGRAPH/MASS SPECTROMETER; GC/MS) ON THE NASA DC-8 TO PROVIDE CONTINUOUS ACCURATE AND SENSITIVE MEASUREMENTS OF A LARGE SUBSET OF NONMETHANE ORGANIC COMPOUNDS (NMOC) INCLUDING MANY CAMPAIGN PRIORITY LEVEL 1 AND 2 SPECIES. BY PROVIDING A FULL HIGH-RESOLUTION MASS SPECTRUM CONTINUOUSLY AT 50 HZ RATE OR BETTER THE TOF MS OFFERS MANY ADVANTAGES OVER OUR PREVIOUSLY-DEPLOYED QUADRUPOLE MS THAT RELIED ON SCANNING A SINGLE ION MASS FRAGMENT FOR EACH COMPOUND OF INTEREST. THE TOF MS ENSURES THAT: (1) NO CHEMICAL INFORMATION IS LOST BY ELIMINATING THE NEED TO PRE-SELECT TARGET IONS PRIOR TO COLLECTING DATA; (2) FULL MASS SPECTRA ARE AVAILABLE FOR ADVANCED COMPOUND IDENTIFICATION EVEN AFTER THE FACT VIA ESTABLISHED MASS SPECTRA LIBRARIES; (3) FAR MORE SPECIES CAN BE QUANTIFIED; (4) NARROW CHROMATOGRAPHIC PEAKS LESS THAN 0.6 S FULL WIDTH AT HALF MAXIMUM (FWHM) DO NOT PRESENT AN ANALYTICAL LIMITATION THAT IS PRESENT IN THE QUADRUPOLE SYSTEM (DUE TO SLOWER SCANNING RATES); (5) HIGH MASS RESOLUTION ALLOWS FOR THE SEPARATION OF ISOBARS A LIMITATION EVEN WITH GC SEPARATION BUT ESPECIALLY WHEN USING FAST GC METHODS; AND (6) GOOD MASS ACCURACY ALLOWS FOR UNAMBIGUOUS IDENTIFICATION OF PEAKS AND CLEAN SEPARATION OF CO-ELUTING SPECIES. THE DETECTION QUALIFICATIONS WILL ENCOMPASS SPECIES WITH MELTING POINTS>-190 C AND BOILING POINTS BETWEEN -45 C AND 220 C. THIS WILL COVER COMPOUNDS IN THE RANGE OF C3-C10 NON-METHANE HYDROCARBONS (INCLUDING ISOPRENE AND SPECIATED MONOTERPENES) C1-C7 OXYGENATED VOLATILE ORGANIC COMPOUNDS INCLUDING ALCOHOLS ALDEHYDES AND KETONES BUT NOT ACIDS C1-C2 HALOCARBONS C1-C4 ALKYL NITRATES HCN CH3CN AND DIMETHYL SULFIDE. WITH THE EXCEPTION OF THE UPGRADED TOF DETECTOR THE TOGA WE WILL PROPOSE TO DEPLOY HAS BEEN USED IN SEVEN PREVIOUS AIRBORNE MISSIONS WITH EXCELLENT PERFORMANCE AND DATA COVERAGE AND IS CURRENTLY A PART OF THE NASA ATMOSPHERIC TOMOGRAPHY (ATOM) PROJECT ON THE NASA DC-8. DURING THESE DEPLOYMENTS A 35-S INTEGRATED SAMPLE WAS COLLECTED AND ANALYZED EVERY 2 MINUTES. USING THE TOF WILL ENABLE FASTER CHROMATOGRAPHY AS IT WILL ALLOW FOR NARROWER PEAKS WHICH WILL HELP US REDUCE OUR DUTY CYCLE TO 1.5 MINUTES. LIMITS OF DETECTION (LODS) FOR THE QUADRUPOLE VERSION ARE LESS THAN OR EQUAL TO ~1 PPTV FOR MOST SPECIES THESE ARE EXPECTED TO BE SIMILAR FOR THE TOF. FURTHERMORE WE ARE DEPLOYING THE TOGA-TOF ON THE NSF/NCAR FOR THE WE-CAN CAMPAIGN IN SUMMER 2018. WE ALSO PROPOSE TO DEPLOY A CANISTER SAMPLING SYSTEM AS AN ADD-ON TO THE TOGA-TOF USING THE RECENTLY DEVELOPED ENTECH SILONITE MINICANS . THIS WILL ALLOW US TO COLLECT WHOLE AIR SAMPLES IN 1 SECOND WHILE SAMPLING THE CENTER OF FIRE PLUMES. THE MINICANS WILL BE ANALYZED WITH THE TOGA-TOF DURING POST-FLIGHT OR ON MAINTENANCE DAYS. WE HAVE BEEN WORKING WITH AERODYNE RESEARCH INC. TO OPTIMIZE OUR DATA ANALYSIS AND PROCESSING. AN AUTOMATED DATA ANALYSIS TOOL WILL ALLOW IN-FLIGHT PROCESSING SO THAT MIXING RATIOS OF KEY SPECIES WILL BE AVAILABLE TO THE MISSION SCIENTIST IN REAL-TIME. THE INSTRUMENT PACKAGE WILL BE FITTED INTO 1.5 GV RACKS AND WILL CONSUME LESS THAN 2000 W OF POWER. BECAUSE THERE IS STILL MUCH TO BE DISCOVERED WITH QUANTIFYING FIRE EMISSIONS THE POWERFUL TOGA-TOF INSTRUMENT IS IDEAL FOR THE FIRECHEM EXPERIMENT AS IT IS CAPABLE OF IDENTIFYING AND QUANTIFYING BOTH KNOWN (TARGETED) AND UNKNOWN (UNTARGETED) SPECIES IN THE CRITICALLY IMPORTANT QUALIFIED RANGE OF VOCS DETECTABLE BY THIS TECHNIQUE. THE TOGA-TOF WILL BE HIGHLY COMPLEMENTARY TO OTHER POTENTIAL ON-BOARD NMOC MEASUREMENTS SUCH AS THE PTR-TOF-MS WHOLE AIR SAMPLE (WAS) CANISTERS AND CIMS INSTRUMENTS., G4326986265, G4736197316
OpenAlex ID: W4293759869