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Abstract. Reactive halogen chemistry in the springtime Arctic causes ozone depletion events and alters the rate of pollution processing. There are still many uncertainties regarding this chemistry, including the multiphase recycling of halogens and how sea ice impacts the source strength of reactive bromine. Adding to these uncertainties are the impacts of a rapidly warming Arctic. We present observations from the CHACHA (CHemistry in the Arctic: Clouds, Halogens, and Aerosols) field campaign based out of Utqiaġvik, Alaska, from mid-February to mid-April of 2022 to provide information on the vertical distribution of bromine monoxide (BrO), which is a tracer for reactive bromine chemistry. Data were gathered using the Heidelberg Airborne Imaging DOAS (differential optical absorption spectroscopy) Instrument (HAIDI) on the Purdue University Airborne Laboratory for Atmospheric Research (ALAR) and employing a unique sampling technique of vertically profiling the lower atmosphere with the aircraft via “porpoising” maneuvers. Observations from HAIDI were coupled to radiative transfer model calculations to retrieve mixing ratio profiles throughout the lower atmosphere (below 1000 m), with unprecedented vertical resolution (50 m) and total information gathered (average of 17.5 degrees of freedom) for this region. A cluster analysis was used to categorize 245 retrieved BrO mixing ratio vertical profiles into four common profile shapes. We often found the highest BrO mixing ratios at the Earth's surface with a mean of nearly 30 pmol mol−1 in the lowest 50 m, indicating an important role for multiphase chemistry on the snowpack in reactive bromine production. Most lofted-BrO profiles corresponded with an aerosol profile that peaked at the same altitude (225 m above the ground), suggesting that BrO was maintained due to heterogeneous reactions on particle surfaces aloft during these profiles. A majority (11 of 15) of the identified lofted-BrO profiles occurred on a single day, 19 March 2022, over an area covering more than 24 000 km2, indicating that this was a large-scale lofted-BrO event. The clustered BrO mixing ratio profiles should be particularly useful for some MAX-DOAS (multi-axis DOAS) studies, where a priori BrO profiles and their uncertainties, used in optimal estimation inversion algorithms, are not often based on previous observations. Future MAX-DOAS studies (and past reanalyses) could rely on the profiles provided in this work to improve BrO retrievals.
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Arctic Reactive Bromine Events Occur in Two Distinct Sets of Environmental Conditions: A Statistical Analysis of 6 Years of Observations
Abstract Tropospheric bromine radicals in the Arctic efficiently remove ambient ozone and oxidize gaseous elemental mercury. Ground‐based bromine monoxide (BrO) observations from the Arctic Ocean and Utqiaġvik (formerly Barrow) are combined with Modern Era Retrospective Analysis for Research and Applications version 2 reanalysis meteorological fields to determine how BrO varies with environmental conditions. The mean seasonal BrO abundance varies from year to year (p < 0.001), while regional variance in mean BrO is not statistically significant (p > 0.11). Principal component analysis derived three important principal components from the environmental data set. The third principal component explains the most variance in BrO and is correlated with low ozone and cold temperatures. This principal component is consistent with high BrO during ozone depletion events at cold temperatures and can work concurrently with each of the other two principal components to generate two distinct environmental types of high BrO events. The first principal component consists of a less‐stable, thick, mixed layer and low atmospheric pressure and is consistent with observations of high BrO in low‐pressure systems (e.g., storms). The second principal component consists of cold and stable conditions and is consistent with high BrO under surface‐based temperature inversions. Our principal component regression model predicted the both the vertical column density of BrO in the lowest 2 km of the troposphere (R = 0.45) and the vertical column density of BrO in the lowest 200 m (R = 0.54). This statistical description of two types of reactive bromine events may help to harmonize space‐based and ground‐based observations.
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- Award ID(s):
- 1602716
- PAR ID:
- 10374896
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 125
- Issue:
- 10
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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