Observations of inorganic bromine (HOBr, BrO, and Br₂) speciation at Barrow, Alaska, in spring 2009

Abstract

[1] Inorganic bromine plays a critical role in ozone and mercury depletions events (ODEs and MDEs) in the Arctic marine boundary layer. Direct observations of bromine species other than bromine oxide (BrO) during ODEs are very limited. Here we report the first direct measurements of hypobromous acid (HOBr) as well as observations of BrO and molecular bromine (Br 2 ) by chemical ionization mass spectrometry at Barrow, Alaska in spring 2009 during the Ocean-Atmospheric-Sea Ice-Snowpack (OASIS) campaign. Diurnal profiles of HOBr with maximum concentrations near local noon and no significant concentrations at night were observed. The measured average daytime HOBr mixing ratio was 10 pptv with a maximum value of 26 pptv. The observed HOBr was reasonably well correlated (R 2 = 0.57) with predictions from a simple steady state photochemical model constrained to observed BrO and HO 2 at wind speeds <6 m s À1 . However, predicted HOBr levels were considerably higher than observations at higher wind speeds. This may be due to enhanced heterogeneous loss of HOBr on blowing snow coincident with higher wind speeds. BrO levels were also found to be higher at elevated wind speeds. Br 2 was observed in significant mixing ratios (maximum = 46 pptv; average = 13 pptv) at night and was strongly anti-correlated with ozone. The diurnal speciation of observed gas phase inorganic bromine species can be predicted by a time-dependent box model that includes efficient heterogeneous recycling of HOBr, hydrogen bromide (HBr), and bromine nitrate (BrONO 2 ) back to more reactive forms of bromine.

Reactive bromine in the low troposphere of Antarctica. Estimations at two research sites

“…The BrO vmr ranges reported herein (Fig. 10) are comparable to previous tropospheric Artic studies (e.g., Tuckermann et al, 1997;Hönninger and Platt, 2002;Prados-Roman et al, 2011;Liao et al, 2012;Peterson et al, 2017;Simpson et al, 2017) and 35 consistent with the few existing Antarctic measurements (e.g., Table 1). By adding the BrO measurements provided in the frame of this work to the few previous ground-based observations performed at Antarctica from different sites, Fig.…”

“…Former works have estimated that the bromine driven ozone loss in the polar atmosphere represents 44% of the total O3 chemical loss (e.g., Liao et al, 2012;Thompson et al, 2017). Therefore, in the sites referred to in this work the shortest (i.e., 20 at highest BrOx and low wind speed) ozone chemical lifetime τO3 expected is 2.6 days at Belgrano and 0.7 days at Marambio.…”

“…Note that previous studies pointed 8 m s -1 as the wind threshold for blowing snow (e.g., Jones et al, 2009) and others indicated that the steady state approximation is valid for wind speeds lower than the 6 m s -1 threshold considered in here (e.g. Liao et al, 2012). 30 Figure 12 shows the 2015 seasonal evolution of the BrOx budget at each station and Fig.…”

“…9), on other days BrO was present in the low troposphere with a double maximum (morning and evening), characteristic of a late spring behaviour and more related to bromine being recycled e.g. through HOBr (e.g., von Pöhler et al, 2010;Liao et al, 2012;Buys et al, 2013). This time and altitude dependence of the BrO distribution 20 in the troposphere reinforces the benefits of the sort of instrumentation employed in this work, which offers vertically resolved information and is able to perform long-term observations.…”

Interactions of bromine, chlorine, and iodine photochemistry during ozone depletions in Barrow, Alaska

“…The inorganic halogen species Br 2 , Cl 2 , BrO, and HOBr were measured in situ at a height of ∼ 1.5 m above the snowpack with a chemical ionization mass spectrometer (CIMS) employing I − ion chemistry. This method, as used in Barrow, and these observations have been published in Liao et al (2011Liao et al ( , 2012Liao et al ( , 2014. ClO was measured at a height of ∼ 3 m above the snowpack via chemical conversion to a stable, halogenated product followed by online separation and detection by gas chromatography with electron capture detection hyde (HCHO) concentrations were measured at 1 Hz frequency from the fixed tower using a tunable diode laser absorption spectrometer as described in Fried et al (1997) and Lancaster et al (2000).…”