Airborne measurements of BrO and the sum of HOBr and Br₂ over the Tropical West Pacific from 1 to 15 km during the CONvective TRansport of Active Species in the Tropics (CONTRAST) experiment

Abstract

A chemical ionization mass spectrometer was used to measure BrO and HOBr + Br2 over the Tropical West Pacific Ocean within the altitude range of 1 to 15 km, during the CONvective TRansport of Active Species in the Tropics (CONTRAST) campaign in 2014. Isolated episodes of elevated BrO (up to 6.6 pptv) and/or HOBr + Br2 (up to 7.3 pptv) were observed in the tropical free troposphere (TFT) and were associated with biomass burning. However, most of the time we did not observe significant BrO or HOBr + Br2 in the TFT and the tropical tropopause layer (TTL) above our limits of detection (LOD). The 1 min average LOD for BrO ranged from 0.6 to 1.6 pptv and for HOBr + Br2 ranged from 1.3 to 3.5 pptv. During one flight, BrO observations from the TTL to the extratropical lowermost stratosphere were used to infer a profile of inorganic bromine (Bry). Based on this profile, we estimated the product gas injection of bromine species into the stratosphere to be 2 pptv. Analysis of Bry partitioning further indicates that BrO levels are likely very low in the TFT environment and that future studies should target the measurement of HBr or atomic Br.

BrO and inferred Br<sub><i>y</i></sub> profiles over the western Pacific: relevance of inorganic bromine sources and a Br<sub><i>y</i></sub> minimum in the aged tropical tropopause layer

“…5). Just prior to the entry into the stratosphere, GT CIMS reported 0.48 ± 0.58 ppt BrO, which is below the GT CIMS level of detection (0.6-1.6 ppt during RF15 for BrO; Chen et al, 2016), and significantly lower than both AMAX-DOAS and CAM-Chem. In the LS, GT CIMS BrO rapidly increases to ∼ 3.8 ppt BrO (averaged for 02:09-02:14 UTC).…”

“…The GV can only probe the TTL closer to the tropopause through latitudinal transects where the relevant region is at lower altitude. The aged TTL as defined in this work is nearly equivalent to the TTL-LMS (tropical tropopause layer-lowermost stratosphere) transition defined in Chen et al (2016); i.e., [CO] is correlated with [O 3 ] with a slope of −0.4. Exceptions to this are that portions of the convective TTL, and a mid-FT filament (RF07), fall on the same line (would be TTL-LMS in Chen et al, 2016), and portions of the aged TTL (RF06, RF15) organize as parallel lines with slopes of −0.03, which would classify as stratospheric in Chen et al (2016).…”

“…The Georgia Tech CIMS (GT CIMS) was on the same GV platform as the AMAX-DOAS and measured BrO and Br 2 + HOBr, with results summarized in Chen et al (2016). There was no overlap between the tropospheric case studies presented here and those in Chen et al (2016); the CIMS had calibration challenges for early flights, while cloudy conditions precluded AMAX-DOAS retrievals for later flights. The Manchester University CIMS (MU CIMS) was aboard the British Aerospace 146 (BAe-146) aircraft as part of the Coordinated Airborne Studies in the Tropics (CAST) project .…”

“…Recent measurements of elevated BrO in the free troposphere (FT) suggest sea-salt sources may contribute to Br y in the FT Wang et al, 2015;Schmidt et al, 2016), but the relative contribution of sea-salt-derived Br y and VSLSderived PGI contributions to stratospheric Br y injection has not, to our knowledge, previously been experimentally evaluated. One objective of the CONvective TRansport of Active Species in the Tropics (CONTRAST) and the Airborne Tropical TRopopause EXperiment (ATTREX) field campaigns (January and February 2014) in Guam was to provide observational constraints to Br y from aircraft measurements of BrO in the upper troposphere-lower stratosphere (UTLS) over the tropical western Pacific Ocean (tWPO; Chen et al, 2016;Jensen et al, 2016;Pan et al, 2017;.…”

“…In addition to DOAS, microwave radiometry has also been employed to measure BrO (Millán et al, 2012;Stachnik et al, 2013). Chemical ionization mass spectrometry (CIMS) measurements of atmospheric Br y , using I − or SF − 6 , have largely been limited to BrO, although BrCl, HOBr, and Br 2 have also been detected (Le Chen et al, 2016;Neuman et al, 2010).…”