Wintertime Arctic Haze :

Anthropogenic and natural emissions contribute to enhanced concentrations of aerosols , so-called Arctic Haze in the Arctic winter and early spring . Models still have difficulties reproducing available observations. Whilst most attention has focused on the contribution of anthropogenic aerosols , there has been less focus on natural components such as :::: with :::: most :::::::: attention ::::::: focusing ::: on :::::::::::: anthropogenic ::::::: aerosols ::::::::::: contributing :: to :::::::: so-called ::::: Arctic :::::: Haze. :::: Less :::::::::: well-studied :::::::::: wintertime : seaspray aerosols (SSA) , including sea-salt sulphate and marine organics, which ::::: under ::::: Arctic ::::: Haze ::::::::: conditions ::: are :::: the ::::: focus 5 :: of ::: this ::::: study ::::: since :::: they : can make an important contribution to fine and coarse mode aerosols, particularly in coastal areas. ::::::::: wintertime ::::: Arctic ::::::: aerosol :::::::::: abundances. :::::::: Analysis :: of ::::: field :::::::: campaign :::: data :::: also :::::: shows :::::::: evidence ::: for :::::::: enhanced ::::: local :::::: sources ::: of :::: SSA :::::::: including :::::: marine ::::::: organics :: at ::::::::: Utqiaġvik :::::::: (northern ::::::: Alaska, :::::: United :::::: States) :::::: during ::::: winter ::::: 2014. : Models tend to underestimate sub-micron, : and overestimate super-micronSSA in polar regions, including in the Arctic region. Quasi-hemispheric runs : , :::: SSA :: in ::: the :::::: Arctic :::::: during :::::: winter, :::::::: including ::: the ::::: base :::::: version : of the Weather Research Forecastmodel, coupled with chem10 istry model (WRF-Chem) are compared to aerosol composition data at remote Arctic sites to evaluate the model performance simulating wintertime Arctic Haze. Results show that the model overestimates sea-salt (sodium and chloride) and nitrate and underestimates sulphate aerosols. Inclusion of more recent ::::: model :::: used :::: here, :::::: which ::::::: includes : a :::::: widely :::: used :::: SSA :::::: source ::::::: function ::::: based :: on :::::::::::::::: Gong et al. (1997). :::::::::::::::: Quasi-hemispheric :::::::::: simulations ::: for :::::: winter :::: 2014 ::::::::: including ::::::: updated wind-speed and sea-surface temperature dependencies for sea-salt emissions, as well as inclusion of marine organic and sea-salt sulphate aerosol emissions 15 leads to better agreement with the observations during wintertime. The model captures better the contribution :::: SSA :::::::: emission ::::::::::: dependencies, :::: and :::::: sources ::: of :::::: marine :::: SSA ::::::: organics :::: and :::::::::::::: sea-salt-sulphate ::::: leads :: to :::::::::: significantly :::::::: improved :::::: model ::::::::::: performance :::::::: compared :: to :::::::::: observations :: at :::::: remote ::::: Arctic ::::: sites, :::::: notably ::: for :::::: coarse :::: mode ::::::: sodium ::: and ::::::: chloride ::::: which ::: are ::::::: reduced. :::: The :::::::: improved ::::: model :::: also :::::::: simulates :::: more ::::::: realistic ::::::::::: contributions of SSA to total mass for different aerosol modes :::::::: inorganic ::::::: aerosols : at :::::::: different :::: sites, ranging from 20-93% in the observations. The sensitivity of modelled SSA to processes influencing SSA production are 20 examined in regional runs over northern Alaska (United States) where the ::: Two ::::: thirds ::: of ::: the :::::::: improved :::::: model ::::::::::: performance