The NO<sub><i>x</i></sub> dependence of bromine chemistry in the Arctic atmospheric boundary layer

Abstract

Abstract. Arctic boundary layer nitrogen oxides (NOx = NO2 + NO) are naturally produced in and released from the sunlit snowpack and range between 10 to 100 pptv in the remote background surface layer air. These nitrogen oxides have significant effects on the partitioning and cycling of reactive radicals such as halogens and HOx (OH + HO2). However, little is known about the impacts of local anthropogenic NOx emission sources on gas-phase halogen chemistry in the Arctic, and this is important because these emissions can induce large variability in ambient NOx and thus local chemistry. In this study, a zero-dimensional photochemical kinetics model was used to investigate the influence of NOx on the unique springtime halogen and HOx chemistry in the Arctic. Trace gas measurements obtained during the 2009 OASIS (Ocean – Atmosphere – Sea Ice – Snowpack) field campaign at Barrow, AK were used to constrain many model inputs. We find that elevated NOx significantly impedes gas-phase halogen radical-based depletion of ozone, through the production of a variety of reservoir species, including HNO3, HO2NO2, peroxyacetyl nitrate (PAN), BrNO2, ClNO2 and reductions in BrO and HOBr. The effective removal of BrO by anthropogenic NOx was directly observed from measurements conducted near Prudhoe Bay, AK during the 2012 Bromine, Ozone, and Mercury Experiment (BROMEX). Thus, while changes in snow-covered sea ice attributable to climate change may alter the availability of molecular halogens for ozone and Hg depletion, predicting the impact of climate change on polar atmospheric chemistry is complex and must take into account the simultaneous impact of changes in the distribution and intensity of anthropogenic combustion sources. This is especially true for the Arctic, where NOx emissions are expected to increase because of increasing oil and gas extraction and shipping activities.

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

“…Trace gases were fitted using the DOAS method (Platt and Stutz, 2008) using the QDOAS software package (Danckaert et al, 2012). The wavelength calibration for each spectrum is precisely determined by measuring the mercury atomic emission at 404.7 nm.…”

“…Absorption by relevant species is fitted simultaneously using the non-linear Marquardt-Levenberg algorithm with full non-linear treatment reserved for shift, stretch, and intensity offset (Danckaert et al, 2012). This is done in finite wavelength windows targeting specific trace gases.…”

Bromine atom production and chain propagation during springtime Arctic ozone depletion events in Barrow, Alaska

“…As discussed in Thompson et al (2015) and further investigated in Custard et al (2015), NO 2 at Barrow can be greater and more variable than at very remote sites due to its proximity to anthropogenic emissions sources. We find that the chain length calculation is relatively insensitive to NO 2 concentrations and so it is robust for the range of conditions encountered at Barrow.…”

“…As discussed by Custard et al (2015), while NO 2 can inhibit the bromine chain through Reactions (R10) and (R12) (i.e., decreasing the chain length), enhanced NO 2 will also reduce available HO 2 , thereby decreasing the HO 2 available to terminate the chain (i.e., increasing the chain length). While the Method 2 calculation does not contain NO 2 in the denominator, the absolute [BrO] is NO x dependent because of Reaction (R10) (Custard et al, 2015), and it is through this effect that high NO x mixing ratios act to decrease the rate of O 3 depletion. In the natural environment, Br 2 production can potentially also be NO x dependent, e.g., via Reaction (R11), followed by Reaction (R7).…”

Molecular Halogens Above the Arctic Snowpack: Emissions, Diurnal Variations, and Recycling Mechanisms

“…A number of previous studies have utilized numerical models to probe reactive halogen chemistry and impacts in the Arctic boundary layer (Calvert & Lindberg, 2003;Cao et al, 2014;Custard et al, 2015Custard et al, , 2016Evans et al, 2003;Fan & Jacob, 1992;Hausmann & Platt, 1994;Kaleschke et al, 2004;Le Bras & Platt, 1995;Lehrer et al, 2004;Liao et al, 2012;Mahajan et al, 2010;Martinez et al, 1999;McConnell et al, 1992;Michalowski et al, 2000;Piot & von Glasow, 2008Saiz-Lopez et al, 2007Sander et al, 1997;Shepson et al, 1996;Spicer et al, 2002;Tackett et al, 2007;Tang & McConnell, 1996;Thomas et al, 2011;Thompson et al, 2015;Toyota et al, 2014;Xie et al, 2008;Zeng et al, 2006;Zhao et al, 2008). The potential importance of recycling mechanisms was first highlighted over two decades ago (Fan & Jacob, 1992;McConnell et al, 1992).…”