TY - JOUR
T1 - Iodine's impact on tropospheric oxidants
T2 - A global model study in GEOS-Chem
AU - Sherwen, T.
AU - Evans, M. J.
AU - Carpenter, L. J.
AU - Andrews, S. J.
AU - Lidster, R. T.
AU - Dix, B.
AU - Koenig, T. K.
AU - Sinreich, R.
AU - Ortega, I.
AU - Volkamer, R.
AU - Saiz-Lopez, A.
AU - Prados-Roman, C.
AU - Mahajan, A. S.
AU - Ordóñez, C.
N1 - © Authors 2016. This content is made available by the publisher under a Creative Commons Attribution Licence. This means that a user may copy, distribute and display the resource providing that they give credit. Users must adhere to the terms of the licence.
PY - 2016/2/2
Y1 - 2016/2/2
N2 - We present a global simulation of tropospheric iodine chemistry within the GEOS-Chem chemical transport model. This includes organic and inorganic iodine sources, standard gas-phase iodine chemistry, and simplified higher iodine oxide (I2OX, X=2, 3, 4) chemistry, photolysis, deposition, and parametrized heterogeneous reactions. In comparisons with recent iodine oxide (IO) observations, the simulation shows an average bias of ~+90% with available surface observations in the marine boundary layer (outside of polar regions), and of ~+73¯% within the free troposphere (350 hPa < p < 900 hPa) over the eastern Pacific. Iodine emissions (3.8 Tg yr-1) are overwhelmingly dominated by the inorganic ocean source, with 76% of this emission from hypoiodous acid (HOI). HOI is also found to be the dominant iodine species in terms of global tropospheric IY burden (contributing up to 70%). The iodine chemistry leads to a significant global tropospheric O3 burden decrease (9.0%) compared to standard GEOS-Chem (v9-2). The iodine-driven OXloss rate1 (748 Tg OX yr-1) is due to photolysis of HOI (78%), photolysis of OIO (21%), and reaction between IO and BrO (1%). Increases in global mean OH concentrations (1.8%) by increased conversion of hydroperoxy radicals exceeds the decrease in OH primary production from the reduced O3 concentration. We perform sensitivity studies on a range of parameters and conclude that the simulation is sensitive to choices in parametrization of heterogeneous uptake, ocean surface iodide, and I2OX (X=2, 3, 4) photolysis. The new iodine chemistry combines with previously implemented bromine chemistry to yield a total bromine- and iodine-driven tropospheric O3 burden decrease of 14.4% compared to a simulation without iodine and bromine chemistry in the model, and a small increase in OH (1.8%). This is a significant impact and so halogen chemistry needs to be considered in both climate and air quality models. Here Ox is defined as O3 + NO2 + 2NO3 + PAN + PMN+PPN + HNO4 + 3N2O5 + HNO3 + BrO + HOBr + BrNO2+2BrNO3 + MPN + IO + HOI + INO2 + 2INO3 + 2OIO+2I2O2 + 3I2O3 + 4I2O4, where PAN=peroxyacetyl nitrate, PPN=peroxypropionyl nitrate, MPN=methyl peroxy nitrate, and MPN=peroxymethacryloyl nitrate.
AB - We present a global simulation of tropospheric iodine chemistry within the GEOS-Chem chemical transport model. This includes organic and inorganic iodine sources, standard gas-phase iodine chemistry, and simplified higher iodine oxide (I2OX, X=2, 3, 4) chemistry, photolysis, deposition, and parametrized heterogeneous reactions. In comparisons with recent iodine oxide (IO) observations, the simulation shows an average bias of ~+90% with available surface observations in the marine boundary layer (outside of polar regions), and of ~+73¯% within the free troposphere (350 hPa < p < 900 hPa) over the eastern Pacific. Iodine emissions (3.8 Tg yr-1) are overwhelmingly dominated by the inorganic ocean source, with 76% of this emission from hypoiodous acid (HOI). HOI is also found to be the dominant iodine species in terms of global tropospheric IY burden (contributing up to 70%). The iodine chemistry leads to a significant global tropospheric O3 burden decrease (9.0%) compared to standard GEOS-Chem (v9-2). The iodine-driven OXloss rate1 (748 Tg OX yr-1) is due to photolysis of HOI (78%), photolysis of OIO (21%), and reaction between IO and BrO (1%). Increases in global mean OH concentrations (1.8%) by increased conversion of hydroperoxy radicals exceeds the decrease in OH primary production from the reduced O3 concentration. We perform sensitivity studies on a range of parameters and conclude that the simulation is sensitive to choices in parametrization of heterogeneous uptake, ocean surface iodide, and I2OX (X=2, 3, 4) photolysis. The new iodine chemistry combines with previously implemented bromine chemistry to yield a total bromine- and iodine-driven tropospheric O3 burden decrease of 14.4% compared to a simulation without iodine and bromine chemistry in the model, and a small increase in OH (1.8%). This is a significant impact and so halogen chemistry needs to be considered in both climate and air quality models. Here Ox is defined as O3 + NO2 + 2NO3 + PAN + PMN+PPN + HNO4 + 3N2O5 + HNO3 + BrO + HOBr + BrNO2+2BrNO3 + MPN + IO + HOI + INO2 + 2INO3 + 2OIO+2I2O2 + 3I2O3 + 4I2O4, where PAN=peroxyacetyl nitrate, PPN=peroxypropionyl nitrate, MPN=methyl peroxy nitrate, and MPN=peroxymethacryloyl nitrate.
UR - http://www.scopus.com/inward/record.url?scp=84957588803&partnerID=8YFLogxK
U2 - 10.5194/acp-16-1161-2016
DO - 10.5194/acp-16-1161-2016
M3 - Article
AN - SCOPUS:84957588803
SN - 1680-7316
VL - 16
SP - 1161
EP - 1186
JO - Atmospheric Chemistry and Physics
JF - Atmospheric Chemistry and Physics
IS - 2
ER -
