Bromine radicals influence global tropospheric chemistry
by depleting ozone and by oxidizing elemental mercury and reduced sulfur
species. Observations typically indicate a 50 % depletion of sea salt
aerosol (SSA) bromide relative to seawater composition, implying that SSA
debromination could be the dominant global source of tropospheric bromine.
However, it has been difficult to reconcile this large source with the
relatively low bromine monoxide (BrO) mixing ratios observed in the marine
boundary layer (MBL). Here we present a new mechanistic description of SSA
debromination in the GEOS-Chem global atmospheric chemistry model with a
detailed representation of halogen (Cl, Br, and I) chemistry. We show that
observed levels of SSA debromination can be reproduced in a manner
consistent with observed BrO mixing ratios. Bromine radical sinks from the
HOBr + S(IV) heterogeneous reactions and from ocean emission of
acetaldehyde are critical in moderating tropospheric BrO levels. The
resulting HBr is rapidly taken up by SSA and also deposited. Observations of SSA debromination at southern midlatitudes in summer suggest that model
uptake of HBr by SSA may be too fast. The model provides a successful
simulation of free-tropospheric BrO in the tropics and midlatitudes in summer,
where the bromine radical sink from the HOBr + S(IV) reactions is
compensated for by more efficient HOBr-driven recycling in clouds compared to
previous GEOS-Chem versions. Simulated BrO in the MBL is generally much
higher in winter than in summer due to a combination of greater SSA emission
and slower conversion of bromine radicals to HBr. An outstanding issue in
the model is the overestimate of free-tropospheric BrO in extratropical
winter–spring, possibly reflecting an overestimate of the HOBr/HBr ratio
under these conditions where the dominant HOBr source is hydrolysis of
BrNO3.
Introduction
Bromine radicals (BrOx≡ Br + BrO) influence global
tropospheric chemistry by depleting ozone and thus OH, as well as by oxidizing
species such as elemental mercury and dimethylsulfide (Saiz-Lopez and von
Glasow, 2012; Simpson et al., 2015; Long et al., 2014). Tropospheric bromine
radical chemistry is initiated by the production of reactive inorganic
bromine (Bry) from sea salt aerosol (SSA) debromination, decomposition
of organobromines primarily of marine origin (CHBr3, CH2Br2,
and CH3Br), and transport from the stratosphere. Within the
Bry family, bromine radicals cycle with non-radical reservoir species such as
HBr, HOBr, BrNO2, BrNO3, Br2, BrCl, and IBr. Loss of
Bry is by wet and dry deposition to the surface, mainly as HBr, which is highly
soluble in water.
Sea salt aerosol (SSA) is thought to be the largest source of tropospheric
bromine. Observations show extensive debromination of SSA relative to
seawater composition (Sander et al., 2003; Newberg et al., 2005). Parrella
et al. (2012) estimate a global Bry source of 1420 Gg Br a-1
from SSA debromination, as compared with 520 Gg a-1 from
organobromines and 36 Gg a-1 from the stratosphere. Volatilization of
bromide from SSA can take place by heterogeneous reactions with HOBr, HOCl,
N2O5, ozone, and ClNO3 (Vogt et al., 1996; Hirokawa et al.,
1998; Keene et al., 1998; Fickert et al., 1999; von Glasow et al., 2002a, b;
Yang et al., 2005; Ordóñez et al., 2012; Saiz-Lopez et al., 2012;
Long et al., 2014). A standing conundrum has been that observations of BrO
in the marine boundary layer (MBL) do not show large enhancements relative
to the free troposphere, where background mixing ratios are typically of the
order of 1 ppt (ppt ≡ pmol mol-1, Leser et al., 2003; Sander et
al., 2003; Theys et al., 2011; Volkamer et al., 2015; Wang et al., 2015; Le
Breton et al., 2017). Ozone observations in the MBL similarly do not show
depletion that would be expected from high mixing ratios of BrO (de Laat and
Lelieveld, 2000; Sherwen et al., 2016). This has led recent global models
not to include SSA debromination as a source of Bry (Schmidt et al.,
2016; Sherwen et al., 2016).
Here we present a new mechanistic description of sea salt debromination in
the GEOS-Chem global 3-D model of tropospheric chemistry, including detailed
representation of halogens (Cl, Br, and I) (Sherwen et al., 2016; Wang et
al., 2019). We find that we can reproduce the observed levels of SSA
debromination while also being consistent with the relatively low BrO mixing
ratios observed in the MBL. This is because the previously recognized fast
production of Bry from SSA debromination is offset by fast removal of Br
atoms by acetaldehyde emitted from the ocean (Toyota et al., 2004; Millet et
al., 2010; Badia et al., 2019) and by fast removal of HOBr by dissolved
SO2 (S(IV)) in cloud (Long et al., 2014; Chen et al., 2017). We examine
the implications for the global budget of tropospheric bromine and
tropospheric oxidants.
Data and methods
We use GEOS-Chem 12.3.0 (10.5281/zenodo.2620535, GEOS-Chem 12.3.0, 2019), which
includes a detailed representation of ozone–NOx–volatile-organic-compound–aerosol–halogen
tropospheric chemistry (Sherwen et al., 2016), to which we have added the
comprehensive tropospheric chlorine chemistry of Wang et al. (2019) with
some additional modifications as described below. The model is driven by
assimilated meteorological data for 2011–2012 from the Modern-Era
Retrospective analysis for Research and Applications, Version 2 (MERRA2),
produced by the NASA Global Modeling and Assimilation Office (Gelaro et al.,
2017). The horizontal resolution of MERRA2 is 0.5∘× 0.625∘
and is degraded here to 4∘× 5∘ for input to GEOS-Chem. Dynamic and chemical time steps are 30
and 60 min, respectively. GEOS-Chem stratospheric chemistry (Eastham et
al., 2014) is linearized following Murray et al. (2012) to serve as boundary
conditions for stratospheric input to the troposphere. The model is spun up
for 1 yr and we use simulation results for 2012.
Tropospheric bromine chemistry in GEOS-Chem was first introduced by Parrella
et al. (2012). Loss of Bry from the troposphere is mainly by deposition
of HBr, which is highly water-soluble unlike HOBr or BrO. Parrella et al. (2012)
found that the acid-catalyzed HOBr +Br- reaction taking place
in liquid-water clouds, ice crystal quasi-liquid surfaces, and aqueous
aerosols was critical for recycling bromide and maintaining background
tropospheric BrO at observed ∼1 ppt levels:
R1HOBr(aq)+Br-+H+→Br2(g)+H2O,R2Br2+hv→2Br,R3Br+O3→BrO+O2.
The current standard version of the model (GEOS-Chem 12.3.0) includes more
extensive heterogeneous bromine chemistry (Schmidt et al., 2016), coupling
to other halogens (Sherwen et al., 2016), HOBr + S(IV) reactions in clouds
(Chen et al., 2017), and oceanic emission of acetaldehyde which reacts
rapidly with Br atoms (Toyota et al., 2004; Millet et al., 2010; Badia et
al., 2019). Wang et al. (2019) more recently added a comprehensive treatment
of tropospheric chlorine chemistry in GEOS-Chem including explicit
accounting of SSA chloride volatilization and aerosol pH. The model does not
attempt to simulate the fast but localized bromine chemistry taking place in
the Arctic MBL in spring due to volatilization of bromine deposited on sea
ice (Simpson et al., 2015).
Here we added several updates to the computation of heterogeneous chemistry
recycling bromine radicals. Uptake of HOBr(aq) by clouds involves
competition between reactions with Br-, Cl-, HSO3-, and
SO32-, as given by Reactions (R1), (R4), and (R5):
HOBr(aq)+Cl-+H+→BrCl(g)+H2O,R5aHOBr(aq)+HSO3-→H2O+BrSO3-,R5bHOBr(aq)+SO32-→OH-+BrSO3-,R5cBrSO3-+H2O→SO42-+Br-+2H+.
Reactions (R1) and (R4) recycle bromine radicals, while Reaction (R5) is effectively a terminal
sink because of HBr deposition. The standard GEOS-Chem code computes the
reactive uptake coefficient (γ) independently for each pathway,
which incorrectly assumes that other pathways do not affect mass transfer.
Here we express the first-order aqueous-phase loss of HOBr as a sum of the
four pathways to compute γ, and we then distribute the loss by
pathways on the basis of the relative rates (see Supplement Sect. S1).
When calculating HOBr uptake by ice crystals, we assume a radius of
38.5 µm based on cloud observations (Fu, 1996) rather than 75 µm
in the standard GEOS-Chem code and further increase the effective surface
area of ice crystals by a factor of 10 to account for their irregular shape
(Schmitt and Heymsfield, 2005). Finally, we correct a registration error for
SSA alkalinity in the standard GEOS-Chem code that caused an underestimate of
alkalinity titration (see Sect. S2). The overall
result of our updates is to have more efficient heterogeneous recycling of
bromine radicals, both in the MBL and in the free troposphere.
The GEOS-Chem SSA simulation is from Jaeglé et al. (2011), who showed
that it could reproduce successfully SSA observations over the oceans from
ship cruises and coastal/island stations, as well as observations of aerosol
optical depth (AOD) from the Aerosol Robotic Network (AERONET) and the MODIS satellite
instrument. The model separates fine (≤0.5µm radius) and coarse
SSA as two separate transported species. The global dry SSA source in our
simulation is 3140 Tg a-1. We emit bromide as part of fine and coarse
SSA with a seawater ratio of 2.11×10-3 kg Br per kilogram of dry SSA
(Sander et al., 2003; Lewis and Schwartz, 2004), since observations show
that fresh SSA has a bromide content equal to that of seawater (Duce and
Woodcock, 1971; Duce and Hoffman, 1976; Turekian et al., 2003). SSA
alkalinity is emitted at a ratio of 0.07 equivalents per kilogram of dry
SSA and is depleted by strong acids following Alexander et al. (2005). The
cloud pH is calculated as described in Alexander et al. (2012) and is
3.5–6.5 for clean marine conditions, consistent with the observed range
(3.8–6.1) reported in the literature (Gioda et al., 2009; Hegg et al.,
1984; Lenschow et al., 1988; Vong et al., 1997; Watanabe et al., 2001).
Activation of SSA bromide takes place by heterogeneous reactions with HOBr,
ozone, and ClNO3 once alkalinity has been titrated and SSA is acidified
(Hirokawa et al., 1998; Keene et al., 1998; Fickert et al., 1999):
R1Br-+HOBr(aq)+H+→Br2+H2O,R7Br-+O3(aq)+H+→HOBr+O2,R8Br-+ClNO3(aq)+H+→BrCl+HNO3.
We also consider parameterized SSA debromination by HOI(aq) following
McFiggans et al. (2002), where HOI(aq) may be taken up from the gas phase or
produced by hydrolysis of INO2 and INO3:
0.15Br-+0.85Cl-+HOI(aq)+H+→0.15IBrR9+0.85ICl+H2O.
Inorganic oceanic iodine (HOI and I2) emissions are from Carpenter et al. (2013).
Unlike for chloride, SSA debromination does not take place by
acid displacement because of the much stronger acidity of HBr than HCl or
HNO3 (Sander et al., 2003). On the contrary, uptake of gas-phase HBr
can lead to bromine enrichment in SSA.
Sander et al. (2003) introduced the dimensionless enrichment factor (EF) as a
measure of SSA debromination. EF is computed from aerosol measurements as
EF=Br-/Na+measuredBr-/Na+seawater,
where aerosol [Na+] is assumed to be mainly from sea salt, a reliable
assumption in marine air. In GEOS-Chem we treat SSA as a chemically inert
tracer and account for sea salt bromide as a separate species; therefore
EF is computed as
EF=Br-/SSASSAaerosolBr-/SSASSAemission.
We sum [Br-] and [SSA] from both fine and coarse SSA to calculate EF. We
will also present EF values for fine and coarse SSA separately.
Results and discussion
Figure 1 (top panel) shows the annual mean SSA bromine enhancement factors
(EFs) in surface air computed by GEOS-Chem and compares to annual mean
observations compiled by Sander et al. (2003) and from Newberg et al. (2005).
We consider six island and four coastal sites with bulk aerosol EF
measurements available for more than 1 year. The observations are for
different years than the GEOS-Chem simulation, but we assume that
interannual variability is a minor source of error. The mean GEOS-Chem EF
averaged over the sites is 0.75±0.23 (±1 standard deviation),
compared with the observed value of 0.66±0.32. SSA bromide over the
Southern Ocean in the model is less depleted (EF∼0.9) than
over the northern midlatitudes (EF∼0.6), because SSA tends to
retain its alkalinity over the Southern Ocean (Alexander et al., 2005;
Schmidt et al., 2016; Fig. S1). Similarly in the
observations, mean EF is 0.78±0.08 over the Southern Ocean compared
with 0.42±0.11 at northern midlatitudes. Most of the SSA
debromination in the model is from Reaction (R1).
Annual mean bromine enrichment factor (EF) of sea salt aerosol (SSA)
in surface air. GEOS-Chem model results (contours) are compared to
observations (circles in a). (a) shows results for total
SSA (fine + coarse), (b) is for coarse SSA (>0.5µm
radius), and (c) is for fine SSA (≤0.5µm
radius). Observations at 10 sites compiled by Sander et al. (2003) and from
Newberg et al. (2005) are superimposed as circles and labeled in order
1–10: Macquarie Island, Crozet Islands, Cape Grim, Amsterdam Island,
Jabiru, Barbados, Bermuda, Mace Head, Bodega Bay, and Hawaii, respectively.
The simulation is for 2012 and the observations are for different years.
Color bar saturates at 2.0. Maximum modeled EF is 75.0.
Seasonal variation of sea salt aerosol (SSA) debromination at Cape
Grim, Tasmania (40.7∘ S, 144.7∘ E). (a) shows
the bromine enrichment factors (EFs) of monthly mean SSA in
surface air. Observations from Ayers et al. (1999) and Sander et al. (2003)
for 1996–1998 are compared to GEOS-Chem model values for 2012. Shading
gives the interannual standard deviation in the observations. (b) shows
the GEOS-Chem monthly SSA emission flux at Cape Grim (site 3 in
Fig. 1) and the SSA alkalinity. The SSA emission flux is for the oceanic
fraction of the Cape Grim grid square.
SSA mass in GEOS-Chem is dominated by the coarse component over the oceans
and by the fine component over land (due to fast dry deposition of the
coarse component). Thus the EF values for bulk SSA over the ocean are dominated
by the coarse component. SSA debromination is more extensive for the fine
component of SSA because the initial supply of bromide is less and loss of
alkalinity is more extensive. Some areas of the ocean have weak SSA bromide
enrichment (EF>1) because of uptake of HBr. Over land the EF values
are dominated by the fine SSA component because the coarse component
deposits close to the coast. These EF values can be very large because
Bry volatilized from the coarse SSA component is then taken up as HBr by the
fine SSA after the coarse component has deposited.
Global annual mean tropospheric budget and cycling of reactive
inorganic bromine (Bry) and sea salt aerosol (SSA) bromide. Results are
from our GEOS-Chem simulation for 2012 including SSA debromination.
Bry is defined as the ensemble of species inside the dashed box. Rates are in
gigagrams of Br per year (Gg Br a-1),
masses in the boxes are in Gg Br, and numbers in brackets are
mean mixing ratios (ppt). Read 5.8(4) as 5.8×104 Gg Br a-1.
Arrows in black are for gaseous reactions, red for photolysis,
purple for heterogeneous reactions in SSA, and green for other heterogeneous
reactions taking place in cloud and sulfate aerosol. Sources and sinks of
total inorganic bromine (Bry+ SSA bromide) are in orange. Arrow thickness scales with its corresponding rate.
The model overestimates the observed EF over the Southern Ocean. This appears
to reflect a seasonal bias in the model. Figure 2 compares the simulated and
observed seasonality at Cape Grim, Tasmania (Ayers et al., 1999; Sander et
al., 2003). To our knowledge, this is the only site for which seasonal
information is available in the observations. The observed EF is 0.6–0.8 for
most of the year, consistent with the model, but decreases to below 0.4 in
summer while the model does not. The summer minimum in the observations has
been attributed to increased SSA acidity (Ayers et al., 1999; Sander et al.,
2003). Indeed, Fig. 2 shows that SSA alkalinity in the model is titrated
in summer due to the combination of weaker SSA emission (lower winds) and
larger photochemical production of strong acids (H2SO4 and
HNO3). This drives volatilization of Bry from SSA, but we find in
the model that the resulting HBr mainly returns to SSA rather than deposits
to the surface because SSA emission is still relatively high. Uptake of HBr
by SSA proceeds in the model with a reactive uptake coefficient γ=1.3×10-8 exp(4290 K/T)
as recommended by IUPAC (Amman et al., 2013) but with large uncertainty, ranging
from -90 % to +860 % at 278 K.
Seasonal variation of zonal mean tropospheric BrO columns in
different latitudinal bands. Monthly GOME-2 BrO observations are for 2007
and taken from Theys et al. (2011); shading represents 1 standard
deviation about the monthly mean GOME-2 BrO columns. GEOS-Chem BrO columns
are sampled at the GOME-2 local overpass time (09:00–10:00). Red lines are
from our standard simulation including sea salt aerosol (SSA) debromination;
blue lines are from a sensitivity simulation without SSA debromination. The
dashed black line indicates observations for 2009–2011 reported by Coburn
et al. (2011) in Florida, USA, without seasonality information. Black crosses
and stars represent average BrO columns measured during aircraft campaigns
over the eastern tropical Pacific (Volkamer et al., 2015; Wang et al., 2015;
Dix et al., 2016) and western tropical Pacific (Koenig et al., 2017),
respectively.
Figure 3 shows the global budget and speciation of tropospheric Bry in
our simulation. This updates a similar figure by Schmidt et al. (2016) to
include SSA debromination, the HOBr + S(IV) reactions in clouds, oceanic
emission of acetaldehyde, and full coupling with the other halogens. SSA
debromination is the largest global source, mainly from Reactions (R1) and (R7)
producing Br2 and HOBr, respectively. The dominant sink of Bry is
uptake of HBr by SSA, rather than deposition, emphasizing the importance of
competition between these two processes in determining the extent of SSA
debromination. Bromine radical (Br) is converted to HBr by formaldehyde,
acetaldehyde, HO2 radical, and ≥ C3 alkenes with relative
contributions of 52 %, 40 %, 7 %, and 1 %, respectively. In the
Schmidt et al. (2016) budget, acetaldehyde contributed only 17 % of this
bromine radical sink; the larger contribution in our simulation reflects its
oceanic emission. Observations from the recent ATom aircraft campaign (Wofsy
et al., 2018) over the remote Pacific and Atlantic show mean MBL
acetaldehyde mixing ratios within 10 % of those simulated by GEOS-Chem
including the Millet et al. (2010) ocean source (Bates et al., 2018).
Vertical profiles of BrO mixing ratios over the tropical Pacific.
Observations from the TORERO (Volkamer et al., 2015; Wang et al., 2015; Dix
et al., 2016), CONTRAST (Chen et al., 2016; Koenig et al., 2017), and CAST
(Le Breton et al., 2017) aircraft campaigns are compared to model values.
Solid black lines indicate mean observed values in 1 km vertical bins and
with standard deviations (shading). We use two independent CONTRAST BrO data
sets. The black line with dots shows the median values (dashed lines are
25 % and 75 % quantiles) as reported in Koenig et al. (2017). The solid
line denotes the mean values from Chen et al. (2016). GEOS-Chem is sampled
along the flight tracks at the time of the measurements. Model results are
shown from our (i) standard simulation including sea salt aerosol debromination
(red lines) and (ii) sensitivity simulations not including SSA debromination
(blue lines) and HOBr + S(IV) reactions (purple lines). Solid lines are
mean values, dotted lines are median values.
The global tropospheric loading of BrO in our simulation is 8.0 Gg Br,
corresponding to a mean tropospheric mixing ratio of 0.86 ppt (1.7 ppt as
daytime average). The BrO loading is higher than in previous GEOS-Chem
versions starting with 3.8 Gg in Parrella et al. (2012), 5.7 Gg in Schmidt
et al. (2016), 6.4 Gg in Sherwen et al. (2016), 3.6 Gg in Chen et al. (2017),
and 4.2 Gg in Wang et al. (2019). Wang et al. (2019) described this
evolution between versions. Our high BrO loading reflects our updates to
HOBr uptake and correction of SSA alkalinity.
Figure 4 compares simulated tropospheric BrO columns with Global Ozone
Monitoring Experiment (GOME)-2 satellite observations from Theys et al. (2011)
as a function of season and for different latitudinal bands. Also
shown are tropospheric columns from ground-based measurements in Florida,
USA (Coburn et al., 2011), and derived from mean aircraft vertical profiles
over the tropical Pacific from the TORERO (Volkamer et al., 2015; Wang et
al., 2015; Dix et al., 2016) and CONTRAST (Koenig et al., 2017) campaigns.
There is general consistency between these observations. Model results are
from our standard simulation and from a sensitivity simulation without SSA
debromination. The standard simulation provides a good fit to the
observations in the tropics but is much too high at extratropical latitudes
in winter and spring. High model mixing ratios under these conditions are
due to high SSA emissions and fast bromide recycling via Reaction (R1), with the latter
due to a large HOBr source from BrNO3 hydrolysis. BrNO3 hydrolysis
mainly takes place in cloud (droplets and ice crystals) rather than in
aerosols. The dominant global sink for BrNO3 is photolysis (Fig. 3),
but under extratropical winter–spring conditions we find that hydrolysis is
more important because of weak radiation. Another reason for the high
modeled BrO in extratropical winter–spring is that removal of Bry via
deposition of HBr becomes slower under these conditions, as described below.
GEOS-Chem mean BrO mixing ratios in surface air in July (a) and
January (b). Locations of BrO observations in Table 1 are shown as
symbols for the closest season. Open circles are ground sites and solid
lines are ship tracks. Flight tracks in the marine boundary layer (<2 km)
during the TORERO (Volkamer et al., 2015; Wang et al., 2015; Dix et
al., 2016), CONTRAST (Chen et al., 2016), and CAST (Le Breton et al., 2017)
aircraft campaigns are shown as pluses, crosses, and dots (gray),
respectively. Daytime BrO mixing ratios are about double the values shown
here since BrO drops to near zero at night. Color bar saturates at 13.3 ppt
near India.
Daytime mixing ratios (ppt) of BrO in the marine boundary layera.
No.LocationTimeObserved bSimulated cReference dGround-based measurements 1Hawaii (20∘ N, 155∘ W)Sep 1999<2.01.112Crete (35∘ N, 26∘ E)Jul–Aug 2000<0.7–1.50.4813Mace Head (53∘ N, 10∘ W)Apr–Oct e<0.3–2.52.11, 2, 34Maine (43∘ N, 71∘ W)Jul–Aug 2004<2.00.4945Tenerife Island (29∘ N, 17∘ W)Jun–Jul 19973.01.016Cabo Verde (17∘ N, 25∘ W)Nov 2006–Jun 20072.5±1.91.45, 6Ship-based measurements 7Atlantic Ocean (30∘ N-37∘ N)Feb and Octf∼1.00.967, 8, 98Atlantic Ocean (33∘ S-27∘ N)Oct 2000<1.0–3.60.977Aircraft-based measurements 9Eastern tropical Pacific Ocean (TORERO)Jan–Feb 20120.26±0.150.2210, 11, 1210Western tropical Pacific Ocean (CONTRAST)Jan–Feb 20140.63±0.740.661311Western tropical Pacific Ocean (CAST)Jan–Feb 20140.28±0.160.3614
a Locations of measurements are shown in Fig. 6.
b Values reported as ranges, means, and means ± standard
deviations depending on availability. The symbol “<” indicates
that BrO is below the corresponding detection limit.
c Mean values for the simulated model year of 2012. The
observations are for different years. Model values are sampled at the
location and time of year of the observations.
d (1) Sander et al. (2003), (2) Saiz-Lopez et al. (2004),
(3) Saiz-Lopez et al. (2006), (4) Keene et al. (2007), (5) Read et al. (2008),
(6) Mahajan et al. (2010), (7) Leser et al. (2003), (8) Martin et al. (2009),
(9) Saiz-Lopez et al. (2012), (10) Volkamer et al. (2015), (11) Wang et al. (2015),
(12) Dix et al. (2016), (13) Chen et al. (2016), and (14) Le Breton et al. (2017)
e From 1996, 1997, and 2002.
f From 2000 and 2007.
Figure 5 compares simulated vertical profiles with aircraft BrO observations
over the tropics in January and February. Schmidt et al. (2016) and Shermen
et al. (2016) reported negative biases of 0.6–1.0 ppt in modeled BrO
compared with TORERO observations in the upper free troposphere. Our
standard simulation shows a much smaller bias (∼0.3 ppt)
because of the impact of faster HOBr uptake on cloud ice (Sect. 2). Figure 5
also shows BrO results from two sensitivity simulations not including SSA
debromination or the HOBr + S(IV) reactions. Model–observation agreement
in those two cases is generally not as good as in our standard simulation.
As shown in Fig. 5, the impact of SSA debromination extends through the
depth of the troposphere by increasing BrO by 0.1–0.5 ppt with larger
impact near the surface. This is generally seen in other seasons over the
tropical latitudes as well (Fig. S2). For the
extratropical latitudes, the impact of SSA debromination on BrO is much
larger (up to 3 ppt) especially in winter–spring, which is also reflected in
BrO columns (Fig. 4). Besides high SSA emissions and fast bromide
recycling as described above, we also find that only ∼15 %
of Bry there is present as HBr (Figs. S3 and S4),
reflecting the relatively lower Br/BrO ratio
(∼0.02 at winter while ∼0.08 at summer) when
radiation is weak. Bry has then a longer lifetime because non-HBr
species are much less water-soluble (Parrella et al., 2012) and can be
effectively transported to the free troposphere.
Figure 6 shows the simulated global distribution of BrO mixing ratios in
surface air in January and July. We attribute the elevated marine surface
BrO in winter time to a combination of greater SSA emission and slower
removal of Bry via deposition of HBr. However, we fail to find enough
information in previous studies to evaluate the modeled seasonality in
marine surface BrO. Only Cabo Verde has seasonal information (Read et al.,
2008; Mahajan et al., 2010) and shows insignificant seasonal variation
consistent with the model, but this is for the tropics. Observations are
compiled in Table 1 with corresponding model values. The model is generally
consistent with observations in showing daytime mixing ratios in the range
0.5–2 ppt, including low BrO (0.3–0.6) in the MBL measured from aircraft
campaigns. The low level of BrO (∼0.3 ppt) over the eastern
tropical Pacific Ocean (Volkamer et al., 2015; Wang et al., 2015; Dix et
al., 2016) observed during the TORERO flight campaign is driven by weak SSA
emission in the austral summer. The higher BrO in CONTRAST than in CAST is
reproduced by the model where it is due to regional variations in SSA
emission. The tropical North Atlantic is enhanced with BrO (1–3 ppt)
relative to other tropical oceans, both in the model and observations
(Tenerife, Cabo Verde). This is due in the model to slow removal of
Bry via dry deposition of BrNO3, resulting in elevated Bry
(and BrO through Bry cycling). We find the production rate of BrNO3 by BrO +NO2
in this region is ∼76 % slower than over the
surrounding Atlantic. Isolated hotspots near India (July) and the Caribbean
(January and July) in the model correspond to localized hotspots of SSA
emissions.
Conclusions
Observations of sea salt aerosol (SSA) debromination over oceans worldwide
imply a large source of bromine radicals in the marine boundary layer (MBL),
yet measured BrO mixing ratios in the MBL are relatively low. Here we
attempted to reconcile these observations with a global simulation of
tropospheric bromine chemistry in the GEOS-Chem model, including detailed
representation of processes.
We find that we can successfully simulate the observations of SSA
debromination in the literature as measured by the SSA bromine enrichment
factor (EF). Most of the debromination in the model is by the HOBr(aq) +Br-+H+ and O3(aq)+Br-+H+ reactions
taking place in acidified SSA. Debromination is more extensive at northern latitudes
than at southern latitudes because of higher acidity. Observations at southern
midlatitudes show extensive debromination in summer that is not captured by
the model, and we attribute this to model competition for HBr between uptake
by SSA and deposition, where HBr uptake by SSA (taken from the IUPAC
recommendation) may be too fast. The model predicts large bromide
enrichments for fine SSA over land (EF>1) as bromine lost from
the coarse SSA transfers as HBr to the fine SSA that is transported inland.
Our model simulation improves over previous GEOS-Chem versions in the
simulation of surface, aircraft, and satellite observations of BrO mixing
ratios in the tropics and summertime midlatitudes. Previous model versions
including SSA debromination overestimated BrO in the MBL and underestimated
it in the free troposphere. Our lower BrO in the MBL reflects the inclusion
of radical sinks to HBr from the HOBr + S(IV) and CH3CHO+ Br
reactions. Our higher BrO in the free troposphere reflects more efficient
recycling of bromine radicals by HOBr reactions in clouds. However, the
model appears to generate excessive free-tropospheric BrO in the
extratropics in winter–spring. A distinctive feature of these conditions in
the model is a HOBr/HBr ratio in excess of unity, reflecting a large source
of HOBr from BrNO3 hydrolysis and the inefficient production of HBr in
the MBL, allowing MBL bromine to be transported to the free troposphere.
Further investigation into the chemistry mechanism and uncertainty may be
needed, including uptake of HBr by SSA, uptake of HOBr by aerosols (Roberts
et al., 2014), BrNO3 hydrolysis, unexplained observations of oxygenated volatile organic compounds in the free troposphere (Volkamer et al., 2015; Anderson et al., 2017;
Badia et al., 2019), and oxidation of bromide by ozone involving the
BrOOO- ozonide (Artiglia et al., 2017).
Data availability
The GEOS-Chem model is available at http://acmg.seas.harvard.edu/geos/
(last access: 9 May 2019).
GEOS-Chem chemistry mechanism and monthly bromine simulation output used in
this study are available at 10.7910/DVN/BADJDE (Zhu, 2019).
The supplement related to this article is available online at: https://doi.org/10.5194/acp-19-6497-2019-supplement.
Author contributions
LZ and DJJ designed the research and wrote the paper; LZ, DJJ,
SDE, MPS, XW, TS, MJE, QC, and BA led the model
development; TKK, RV, LGH, ML, TJB, and CJP provided BrO
observations.
Competing interests
The authors declare that they have no conflict of
interest.
Acknowledgements
This work was supported by the NSF Atmospheric Chemistry Program. We
acknowledge contributions from the TORERO, CONTRAST, and CAST science team.
We thank Dexian Chen for the CONTRAST BrO observations. Qianjie Chen and Becky
Alexander acknowledge support from NSF AGS 1343077. Rainer
Volkamer and Theodore K. Koenig acknowledge
funding from NSF AGS-1620530.
Financial support
This research has been supported by the NSF (Atmospheric Chemistry Program
and grant nos. NSF AGS 1343077 and AGS-1620530).
Review statement
This paper was edited by Markus Ammann and reviewed by Rolf Sander and one anonymous referee.
ReferencesAlexander, B., Park, R. J., Jacob, D. J., Li, Q. B., Yantosca, R. M.,
Savarino, J., Lee, C. C. W., and Thiemens, M. H.: Sulfate formation in
sea-salt aerosols: Constraints from oxygen isotopes, J. Geophys. Res., 110,
D10307, 10.1029/2004JD005659, 2005.Alexander, B., Allman, D. J., Amos, H. M., Fairlie, T. D., Dachs, J, Hegg,
D. A., and Sletten, R. S.: Isotopicconstraints on the formation pathways of
sulfate aerosol in the marine boundary layer of the subtropical northeast
Atlantic Ocean, J. Geophys. Res., 117, D06304, 10.1029/2011JD016773,
2012.Ammann, M., Cox, R. A., Crowley, J. N., Jenkin, M. E., Mellouki, A., Rossi,
M. J., Troe, J., and Wallington, T. J.: Evaluated kinetic and photochemical
data for atmospheric chemistry: Volume VI – heterogeneous reactions with
liquid substrates, Atmos. Chem. Phys., 13, 8045–8228,
10.5194/acp-13-8045-2013, 2013.Anderson, D. C., Nicely, J. M., Wolfe, G. M., Hanisco, T. F., Salawitch, R.
J., Canty, T. P., Dickerson, R. R., Apel, E. C., Baidar, S., Bannan, T. J.,
Blake, N. J., Chen, D., Dix, B., Fer- nandez, R. P., Hall, S. R., Hornbrook,
R. S., Gregory Huey, L., Josse, B., Jöckel, P., Kinnison, D. E., Koenig, T.
K., Le Breton, M., Marécal, V., Morgenstern, O., Oman, L. D., Pan, L. L.,
Percival, C., Plummer, D., Revell, L. E., Rozanov, E., Saiz-Lopez, A.,
Stenke, A., Sudo, K., Tilmes, S., Ullmann, K., Volkamer, R., Weinheimer, A.
J., and Zeng, G.: Formaldehyde in the Tropical Western Pacific: Chemical
Sources and Sinks, Convective Transport, and Representation in CAM-Chem and
the CCMI Models, J. Geophys. Res.-Atmos., 122, 11201–11226,
10.1002/2016JD026121, 2017.Artiglia, L., Edebeli, J., Orlando, F., Chen, S., Lee, M.-T., Corral Arroyo,
P., Gilgen, A., Bartels-Rausch, T., Kleibert, A., Vaz-dar, M., Andres
Carignano, M., Francisco, J. S., Shepson, P. B., Gladich, I., and Ammann,
M.: A surface-stabilized ozonide trig- gers bromide oxidation at the aqueous
solution-vapour interface, Nat. Commun., 8, 700,
10.1038/s41467-017-00823-x, 2017.
Ayers, G. P., Gillett, R. W., Cainey, J. M., and Dick, A. L.: Chloride and
bromide loss from sea-salt particles in southern ocean air, J. Atmos. Chem.,
33, 299–319, 1999.Badia, A., Reeves, C. E., Baker, A. R., Saiz-Lopez, A., Volkamer, R., Koenig,
T. K., Apel, E. C., Hornbrook, R. S., Carpenter, L. J., Andrews, S. J.,
Sherwen, T., and von Glasow, R.: Importance of reactive halogens in the
tropical marine atmosphere: a regional modelling study using WRF-Chem, Atmos.
Chem. Phys., 19, 3161–3189, 10.5194/acp-19-3161-2019, 2019.
Bates, K. H., Kim, M., and Jacob, D. J.: New Constraints on Remote
Tropospheric Budgets of Oxidized VOCs, 15th IGAC Science Conference,
Takamatsu, Kagawa, Japan, 2018.Carpenter, L. J., MacDonald, S. M., Shaw, M. D., Kumar, R., Saunders, R. W.,
Parthipan, R., Wilson, J., and Plane, J. M. C.: Atmospheric iodine levels
influenced by sea surface emissions of inorganic iodine, Nat. Geosci., 6,
108–111, 10.1038/ngeo1687, 2013.Chen, D., Huey, L. G., Tanner, D. J., Salawitch, R. J., Anderson, D. C.,
Wales, P. A., Pan, L. L., Atlas, E. L., Hornbrook, R. S., Apel, E. C.,
Blake, N. J., Campos, T. L., Donets, V., Flocke, F. M., Hall, S. R.,
Hanisco, T. F., Hills, A. J., Honomichl, S. B., Jensen, J. B., Kaser, L.,
Montzka, D. D., Nicely, J. M., Reeves, J. M., Riemer, D. D., Schauffler, S.
M., Ullmann, K., Weinheimer, A. J., and Wolfe, G. M.: 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, J. Geophys. Res.-Atmos., 121, 12560–12578,
10.1002/2016JD025561, 2016.Chen, Q., Schmidt, J. A., Shah, V., Jaegleì, L., Sherwen, T., and Alexander,
B.: Sulfate production by reactive bromine: Implications for the global
sulfur and reactive bromine budgets, Geophys. Res. Lett., 44, 7069–7078,
10.1002/2017GL073812, 2017.Coburn, S., Dix, B., Sinreich, R., and Volkamer, R.: The CU ground MAX-DOAS
instrument: characterization of RMS noise limitations and first measurements
near Pensacola, FL of BrO, IO, and CHOCHO, Atmos. Meas. Tech., 4, 2421–2439,
10.5194/amt-4-2421-2011, 2011.de Laat, A. T. J. and Lelieveld, J.: The diurnal O3 cycle in the
tropical and subtropical marine boundary layer, J. Geophys. Res., 105, 11547–11559, 2000.Dix, B., Koenig, T. K., and Volkamer, R.: Parameterization retrieval of trace
gas volume mixing ratios from Airborne MAX-DOAS, Atmos. Meas. Tech., 9,
5655–5675, 10.5194/amt-9-5655-2016, 2016.
Duce, R. A. and Hoffman, E.: Chemical fractionation at the air/sea
interface, Annu. Rev. Earth Planet. Sci., 4, 187–228, 1976.
Duce, R. A. and Woodcock, A. H.: Difference in chemical composition of
atmospheric sea salt particles produced in the surf zone and on the open sea
in Hawaii, Tellus, 23, 427–435, 1971.Eastham, S. D., Weisenstein, D. K., and Barrett, S. R. H.: Development and
evaluation of the unified tropospheric–stratospheric chemistry extension
(UCX) for the global chemistry-transport model GEOS-Chem, Atmos. Environ.,
89, 52–63, 10.1016/j.atmosenv.2014.02.001, 2014.Fickert, S., Adams, J. W., and Crowley, J. N.: Activation of Br2 and
BrCl via uptake of HOBr onto aqueous salt solutions, J. Geophys. Res., 104D,
23719–23727, 1999.
Fu, Q.: An accurate parameterization of the solar radiative properties of
cirrus clouds for climate models, J. Climate, 9, 2058–2082, 1996.Gelaro, R., McCarty, W., Suárez, M. J., Todling, R., Molod, A., Takacs, L.,
Randles, C. A., Darmenov, A., Bosilovich, M. G., Re- ichle, R., Wargan, K.,
Coy, L., Cullather, R., Draper, C., Akella, S., Buchard, V., Conaty, A., da
Silva, A. M., Gu, W., Kim, G.- K., Koster, R., Lucchesi, R., Merkova, D.,
Nielsen, J. E., Partyka, G., Pawson, S., Putman, W., Rienecker, M.,
Schubert, S. D., Sienkiewicz, M., and Zhao, B.: The Modern-Era Retrospective
Analysis for Research and Applications, Version 2 (MERRA-2), J. Climate, 30,
5419–5454, 10.1175/JCLI-D-16-0758.1, 2017.GEOS-Chem 12.3.0: The International GEOS-Chem User Community, Zenodo,
10.5281/zenodo.2620535, 2019.Gioda, A., Mayol-Bracer, O. L., Morales-García, F., Collett, J.,
Decesari, S., Emblico, L., Facchini, M. C., Morales-De Jesús, R. J.,
Mertes, S., Borrmann, S., Walter, S., and Schneider, J.: Chemical
Composition of Cloud Water in the Puerto Rican Tropical Trade Wind Cumuli,
Water Air Soil Pollut., 200, 3–14, 10.1007/s11270-008-9888-4, 2009.Hegg, D. A., Radke, L. F., and Hobbs, P. V. : Measurements of
Transformations in the Physical and Chemical Properties of Clouds Associated
with Onshore Flow in Washington State, J. Appl. Clim. Meteorol., 23,
979–984, 10.1175/1520-0450(1984)023<0979:MOTITP>2.0.CO;2, 1984.
Hirokawa, J., Onaka, K., Kajii, Y., and Akimoto, H.: Heterogeneous processes
involving sodium halide particles and ozone: Molecular bromine release in
the marine boundary layer in the absence of nitrogen oxides, Geophys. Res.
Lett., 25, 2449–2452, 1998.Jaeglé, L., Quinn, P. K., Bates, T. S., Alexander, B., and Lin, J.-T.: Global
distribution of sea salt aerosols: new constraints from in situ and remote
sensing observations, Atmos. Chem. Phys., 11, 3137–3157,
10.5194/acp-11-3137-2011, 2011.
Keene, W. C., Sander, R., Pszenny, A. A. P., Vogt, R., Crutzen, P. J., and
Galloway, J. N.: Aerosol pH in the marine boundary layer: A review and model
evaluation, J. Aerosol Sci., 29, 339–356, 1998.Keene, W. C., Stutz, J., Pszenny, A. A. P., Maben, J. R., Fischer, E. V.,
Smith, A. M., von Glasow, R., Pechtl, S., Sive, B. C., and Varner, R. K.:
Inorganic chlorine and bromine in coastal New England air during summer, J.
Geophys. Res., 112, D10S12, 10.1029/2006JD007689, 2007.Koenig, T. K., Volkamer, R., Baidar, S., Dix, B., Wang, S., Anderson, D. C.,
Salawitch, R. J., Wales, P. A., Cuevas, C. A., Fernandez, R. P., Saiz-Lopez,
A., Evans, M. J., Sherwen, T., Jacob, D. J., Schmidt, J., Kinnison, D.,
Lamarque, J.-F., Apel, E. C., Bresch, J. C., Campos, T., Flocke, F. M., Hall,
S. R., Honomichl, S. B., Hornbrook, R., Jensen, J. B., Lueb, R., Montzka, D.
D., Pan, L. L., Reeves, J. M., Schauffler, S. M., Ullmann, K., Weinheimer, A.
J., Atlas, E. L., Donets, V., Navarro, M. A., Riemer, D., Blake, N. J., Chen,
D., Huey, L. G., Tanner, D. J., Hanisco, T. F., and Wolfe, G. M.: BrO and
inferred Bry profiles over the western Pacific: relevance of inorganic
bromine sources and a Bry minimum in the aged tropical tropopause layer,
Atmos. Chem. Phys., 17, 15245–15270,
10.5194/acp-17-15245-2017, 2017.
Le Breton, M., Bannan, T. J., Shallcross, D. E., Khan, M. A., Evans, M. J.,
Lee, J., Lidster, R., Andrews, S., Carpenter, L., Schmidt, J., Jacob, D.,
Harris, N. R. P., Bauguitte, S.-J., Gallagher, M., Bacak, A., Leather, K.
E., and Percival, C. J.: Enhanced ozone loss by active inorganic bromine
chemistry in the tropical troposphere, Atmos. Environ., 155, 21–28, 2017.Lenschow, D. H., Paluch, I. R., Bandy, A. R., Pearson Jr., R., Kawa, S. R.,
Weaver, C. J., Huebert, B. J., Kay, J. G., Thornton, D. C., and Driedger
III, A. R.: Dynamics and Chemistry of MarineStratocumulus (DYCOMS)
experiment, Bull. Am. Meteorol. Soc., 69, 1058–1067,
10.1175/1520-0477(1988)069<1058:DACOMS>2.0.CO;2,
1988.Leser, H., Hönninger, G., and Platt, U.: MAX-DOAS Measure-ments
of BrO and NO2 in the Marine Boundary Layer, Geophys. Res. Lett.,
30, 1537, 10.1029/2002GL015811, 2003.
Lewis, E. R. and Schwartz, S. E.: Sea Salt Aerosol Production: Mechanisms,
Methods, Measurements and Models – A Critical Review, AGU, 413 pp.,
Washington, D. C., 2004.Long, M. S., Keene, W. C., Easter, R. C., Sander, R., Liu, X., Kerkweg, A.,
and Erickson, D.: Sensitivity of tropospheric chemical composition to
halogen-radical chemistry using a fully coupled size-resolved multiphase
chemistry-global climate system: halogen distributions, aerosol composition,
and sensitivity of climate-relevant gases, Atmos. Chem. Phys., 14, 3397–3425,
10.5194/acp-14-3397-2014, 2014.Mahajan, A. S., Plane, J. M. C., Oetjen, H., Mendes, L., Saunders, R. W.,
Saiz-Lopez, A., Jones, C. E., Carpenter, L. J., and McFiggans, G. B.:
Measurement and modelling of tropospheric reactive halogen species over
the tropical Atlantic Ocean, Atmos. Chem. Phys., 10, 4611–4624, 10.5194/acp-10-4611-2010, 2010.Martin, M., Pöhler, D., Seitz, K., Sinreich, R., and Platt, U.: BrO
measurements over the Eastern North-Atlantic, Atmos. Chem. Phys., 9,
9545–9554, 10.5194/acp-9-9545-2009, 2009.McFiggans, G., Cox, R. A., Mossinger, J. C., Allan, B. J., and Plane, J. M.
C.: Active chlorine release from marine aerosols: Roles for reactive iodine
and nitrogen species, J. Geophys. Res.-Atmos., 107, ACH10-1–ACH10-13,
10.1029/2001jd000383, 2002.Millet, D. B., Guenther, A., Siegel, D. A., Nelson, N. B., Singh, H. B., de
Gouw, J. A., Warneke, C., Williams, J., Eerdekens, G., Sinha, V., Karl, T.,
Flocke, F., Apel, E., Riemer, D. D., Palmer, P. I., and Barkley, M.: Global
atmospheric budget of acetaldehyde: 3-D model analysis and constraints from
in-situ and satellite observations, Atmos. Chem. Phys., 10, 3405–3425,
10.5194/acp-10-3405-2010, 2010.Murray, L. T., Jacob, D. J., Logan, J. A., Hudman, R. C., and Koshak, W. J.:
Optimized regional and interannual variability of lightning in a global
chemical transport model constrained by LIS/OTD satellite data, J. Geophys.
Res.-Atmos., 117, D20307, 10.1029/2012JD017934, 2012.Newberg, J. T., Matthew, B. M., and Anastasio, C.: Chloride and bromide
depletions in sea-salt particles over the northeastern Pacific Ocean, J.
Geophys. Res., 110, D06209, 10.1029/2004JD005446, 2005.Ordóñez, C., Lamarque, J.-F., Tilmes, S., Kinnison, D. E., Atlas, E.
L., Blake, D. R., Sousa Santos, G., Brasseur, G., and Saiz-Lopez, A.:
Bromine and iodine chemistry in a global chemistry-climate model:
description and evaluation of very short-lived oceanic sources, Atmos. Chem.
Phys., 12, 1423–1447, 10.5194/acp-12-1423-2012, 2012.Parrella, J. P., Jacob, D. J., Liang, Q., Zhang, Y., Mickley, L. J., Miller,
B., Evans, M. J., Yang, X., Pyle, J. A., Theys, N., and Van Roozendael, M.:
Tropospheric bromine chemistry: implications for present and pre-industrial
ozone and mercury, Atmos. Chem. Phys., 12, 6723–6740,
10.5194/acp-12-6723-2012, 2012.Read, K. A., Mahajan, A. S., Carpenter, L. J., Evans, M. J., Faria, B. V.
E., Heard, D. E., Hopkins, J. R., Lee, J. D., Moller, S. J., Lewis, A. C.,
Mendes, L., McQuaid, J. B., Oetjen, H., Saiz-Lopez, A., Pilling, M. J., and
Plane, J. M. C.: Extensive halogen-mediated ozone destruction over the
tropical Atlantic Ocean, Nature, 453, 1232–1235, 10.1038/nature07035,
2008.Roberts, T. J., Jourdain, L., Griffiths, P. T., and Pirre, M.: Re-evaluating
the reactive uptake of HOBr in the troposphere with implications for the
marine boundary layer and volcanic plumes, Atmos. Chem. Phys., 14,
11185–11199, 10.5194/acp- 14-11185-2014, 2014.Saiz-Lopez, A. and von Glasow, R.: Reactive halogen chem- istry in the
troposphere, Chem. Soc. Rev., 41, 6448–6472, 10.1039/c2cs35208g, 2012.Saiz-Lopez, A., Plane, J. M. C., and Shillito, J. A.: Bromine oxide in the
mid-latitude marine boundary layer, Geophys. Res. Lett., 31,
L03111, 10.1029/2003GL018956, 2004.Saiz-Lopez, A., Shillito, J. A., Coe, H., and Plane, J. M. C.: Measurements
and modelling of I2, IO, OIO, BrO and NO3 in the mid-latitude
marine boundary layer, Atmos. Chem. Phys., 6, 1513–1528,
10.5194/acp-6-1513-2006, 2006.Saiz-Lopez, A., Lamarque, J.-F., Kinnison, D. E., Tilmes, S.,
Ordóñez, C., Orlando, J. J., Conley, A. J., Plane, J. M. C.,
Mahajan, A. S., Sousa Santos, G., Atlas, E. L., Blake, D. R., Sander, S. P.,
Schauffler, S., Thompson, A. M., and Brasseur, G.: Estimating the climate
significance of halogen-driven ozone loss in the tropical marine
troposphere, Atmos. Chem. Phys., 12, 3939–3949,
10.5194/acp-12-3939-2012, 2012.Sander, R., Keene, W. C., Pszenny, A. A. P., Arimoto, R., Ayers, G. P.,
Baboukas, E., Cainey, J. M., Crutzen, P. J., Duce, R. A., Hönninger, G.,
Huebert, B. J., Maenhaut, W., Mihalopoulos, N., Turekian, V. C., and Van
Dingenen, R.: Inorganic bromine in the marine boundary layer: a critical
review, Atmos. Chem. Phys., 3, 1301–1336,
10.5194/acp-3-1301-2003, 2003.Schmidt, J. A., Jacob, D. J., Horowitz, H. M., Hu, L., Sherwen, T., Evans,
M. J., Liang, Q., Suleiman, R. M., Oram, D. E., Le Breton, M., Percival, C.
J., Wang, S., Dix, B., and Volkamer, R.: Modeling the observed tropospheric
BrO background: Importance of multiphase chemistry and implications for
ozone, OH, and mercury, J. Geophys. Res.-Atmos., 121, 11819–11835,
10.1002/2015JD024229, 2016.
Schmitt, C. G. and Heymsfield, A. J.: Total Surface Area Estimates for
Individual Ice Particles and Particle Populations, J. Appl. Meteor., 44,
467–474, 2005.Sherwen, T., Schmidt, J. A., Evans, M. J., Carpenter, L. J., Großmann,
K., Eastham, S. D., Jacob, D. J., Dix, B., Koenig, T. K., Sinreich, R.,
Ortega, I., Volkamer, R., Saiz-Lopez, A., Prados-Roman, C., Mahajan, A. S.,
and Ordóñez, C.: Global impacts of tropospheric halogens (Cl, Br, I)
on oxidants and composition in GEOS-Chem, Atmos. Chem. Phys., 16,
12239–12271, 10.5194/acp-16-12239-2016, 2016.Simpson, W. R., Brown, S. S., Saiz-Lopez, A., Thornton, J. A., and von
Glasow, R.: Tropospheric Halogen Chemistry: Sources, Cycling, and Impacts,
Chem. Rev., 115, 4035–4062, 10.1021/cr5006638, 2015.Theys, N., Van Roozendael, M., Hendrick, F., Yang, X., De Smedt, I.,
Richter, A., Begoin, M., Errera, Q., Johnston, P. V., Kreher, K., and De
Mazière, M.: Global observations of tropospheric BrO columns using
GOME-2 satellite data, Atmos. Chem. Phys., 11, 1791–1811,
10.5194/acp-11-1791-2011, 2011.Toyota, K., Kanaya, Y., Takahashi, M., and Akimoto, H.: A box model study on
photochemical interactions between VOCs and reactive halogen species in the
marine boundary layer, Atmos. Chem. Phys., 4, 1961–1987,
10.5194/acp-4-1961-2004, 2004.Turekian, V. C., Macko, S. A., and Keene, W. C.: Concentrations, isotopic
compositions, and sources of size-resolved, particulate organic carbon and
oxalate in near-surface marine air at Bermuda during spring, J. Geophys.
Res., 108D, 4157, 10.1029/2002JD002053, 2003.
Vogt, R., Crutzen, P. J., and Sander, R.: A mechanism for halogen release
from sea-salt aerosol in the remote marine boundary layer, Nature, 383,
327–330, 1996.Volkamer, R., Baidar, S., Campos, T. L., Coburn, S., DiGangi, J. P., Dix,
B., Eloranta, E. W., Koenig, T. K., Morley, B., Ortega, I., Pierce, B. R.,
Reeves, M., Sinreich, R., Wang, S., Zondlo, M. A., and Romashkin, P. A.:
Aircraft measurements of BrO, IO, glyoxal, NO2, H2O,
O2-O2 and aerosol extinction profiles in the tropics: comparison
with aircraft-/ship-based in situ and lidar measurements, Atmos. Meas.
Tech., 8, 2121–2148, 10.5194/amt-8-2121-2015, 2015.Vong, R. J., Baker, B. M., Brechtel, F. J., Collier, R. T., Harris, J. M.,
Kowalski, A. S., McDonald, N. C., and Mcinnes, L. M. : Ionic and trace
element composition of cloudwater collected on the Olympic peninsula of
Washington State, Atmos. Environ., 31, 1991–2001,
10.1016/S1352-2310(96)00337-8, 1997.von Glasow, R., Sander, R., Bott, A., and Crutzen, P. J.: Modeling halogen
chemistry in the marine boundary layer. 1. Cloud-free MBL, J. Geophys. Res.,
107D, 4341, 10.1029/2001JD000942, 2002a.von Glasow, R., Sander, R., Bott, A., and Crutzen, P. J.: Modeling halogen
chemistry in the marine boundary layer. 2. Interactions with sulfur and the
cloud-covered MBL, J. Geophys. Res., 107D, 4323, 10.1029/2001JD000943,
2002b.
Wang, S.-Y., Schmidt, J., Baidar, S., Coburn, S., Dix, B., Koenig, T., Apel,
E., Bowdalo, D., Campos, T., Eloranta, E., Evans, M., DiGangii, J., Zondlo,
M., Gao, R.-S., Haggerty, J., Hall, S., Hornbrook, R., Jacob, D., Morley,
B., Pierce, B., Reeves, M., Romashkin, P., ter Schure, A., and Volkamer, R.:
Active and widespread halogen chemistry in the tropical and subtropical free
troposphere, P. Natl. Acad. Sci. USA, 112, 9281–9286,
10.1073/pnas.1505142112, 2015.Wang, X., Jacob, D. J., Eastham, S. D., Sulprizio, M. P., Zhu, L., Chen, Q.,
Alexander, B., Sherwen, T., Evans, M. J., Lee, B. H., Haskins, J. D.,
Lopez-Hilfiker, F. D., Thornton, J. A., Huey, G. L., and Liao, H.: The role
of chlorine in global tropospheric chemistry, Atmos. Chem. Phys., 19,
3981–4003, 10.5194/acp-19-3981-2019, 2019.Watanabe, K., Ishizaka, I., and Takenaka, C. : Chemical characteristics of
cloud water overthe Japan Sea and the northwestern Pacific Ocean near the
central partof Japan: Airborne measurements, Atmos. Environ., 35, 645–655,
10.1016/S1352-2310(00)00358-7, 2001.Wofsy, S. C., Apel, E., Blake, D. R., Brock, C. A., Brune, W. H., Bui, T.
P., Daube, B. C., Dibb, J. E., Diskin, G. S., Elki- ins, J. W., Froyd, K.,
Hall, S. R., Hanisco, T. F., Huey, L. G., Jimenez, J. L., McKain, K.,
Montzka, S. A., Ryerson, T. B., Schwarz, J. P., Stephens, B. B., Weinzierl,
B., and Wennberg, P.: ATom: Merged Atmospheric Chemistry, Trace Gases, and
Aerosols, ORNL DAAC, Oak Ridge, Tennessee, USA,
10.3334/ORNLDAAC/1581, 2018.Yang, X., Cox, R., Warwick, N., Pyle, J., Carver, G., O'Connor, F., and
Savage, N.: Tropospheric bromine chemistry and its impacts on ozone: A model
study, J. Geophys. Res., 110, D23311, 10.1029/2005JD006244, 2005.Zhu, L.: GEOS-Chem chemistry mechanism and monthly bromine simulation output,
Harvard Dataverse, V2, 10.7910/DVN/BADJDE, 2019.