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Authors: Shenolikar, Justin
Title: Nighttime Radical NOx Chemistry by CRD
Online publication date: 19-Jan-2021
Year of first publication: 2021
Language: english
Abstract: The following work presents measurements of NO2, NO3, N2O5, and organic nitrates (ΣPNs (R(O)O2NO2; and ΣANs (RONO2)) made by 3 years of measurements by a 5-channel cavity ringdown spectroscopy (5- CRD) instrument over the course of two field campaigns and multiple laboratory experiments. The results of these two campaigns are discussed within. The 2017 AQABA ship campaign reports measurements of NO2, NO3 and N2O5 from a mixture of highlypolluted and clean marine environments around the Arabian Peninsula and eastern Mediterranean Sea. NO3 and N2O5 mixing ratios over the detection limits seen over 30 of a possible 60 nights during the nights, with mixing ratios of 12 ± 18 ppt for NO3 (max: 146 ppt) and 23 ± 35 ppt (max: 295 ppt) for N2O5, respectively. This corresponds to a median NO3 lifetime of 65.5 seconds (~0.0153 s-1 reactivity) across the entire campaign, although this was found to be highly variable according to the region. DMS was found to be the single largest contributor (20 – 25%) in each region to controlling the lifetime of NO3, though reactions with anthropogenic VOCs, while generally negligible were a regionally important sink in the Persian Gulf. Heterogeneous uptake onto the surface of particles was limited by high temperatures and contributed only a small fraction to reactivity (~5%). Most reactivity (40 – 80%, depending on region) could not be accounted for in the measurements made during AQABA, though an analysis within suggests that ship emissions may contribute strongly to this and shows that SO2 can be used marker to estimate reactivity. Results further suggest that nighttime removal of NOx was considerably more efficient (factor 2 – 3) than during the day in 4 out of 5 of the AQABA regions, despite longer days, high [OH] concentrations and approximately similar NO2 loss rates with OH and O3. The 2018 SAPHIR campaign reports measurements of NO2, NO3, N2O5, ΣPNs and ΣANs from a series of chamber experiments studying the reaction of NO3 + isoprene. Measurements of NO2, NO3 and N2O5 are presented in a statistical intercomparison against other instruments. NO2 measurements from three instruments, including the 5-CRD, report strong agreement in linear regression analysis with high slopes (> 0.9), high R2 values (> 0.9) and generally insignificant intercepts. NO3 and N2O5 comparisons report high levels of agreement with slopes within instrument uncertainties (1.0 and 0.95); high R2 (> 0.9) and intercepts generally consistent with limits of detection. ΣPNs and ΣANs data show possibility of thermal dissociation of isoprene nitrates at temperatures far lower than previously expected (beginning at 430 K), the implications of which are discussed. Gas phase yields of RONO2 from the reaction of NO3 + isoprene were determined as 0.81 ± 0.17 when taken all together but yields from individual experiments were found to be highly variable with significant uncertainty.
DDC: 540 Chemie
540 Chemistry and allied sciences
550 Geowissenschaften
550 Earth sciences
Institution: Johannes Gutenberg-Universität Mainz
Department: FB 09 Chemie, Pharmazie u. Geowissensch.
Place: Mainz
URN: urn:nbn:de:hebis:77-openscience-48d1458b-8418-4ff7-bce6-2ca7374433606
Version: Original work
Publication type: Dissertation
License: In Copyright
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Extent: 168 Seiten
Appears in collections:JGU-Publikationen

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