Identification of sources and formation processes of atmospheric sulfate by sulfur isotope and scanning electron microscope measurements
80
Citation
78
Reference
10
Related Paper
Citation Trend
Abstract:
Atmospheric sulfate aerosols have a cooling effect on the Earth's surface and can change cloud microphysics and precipitation. China has heavy loading of sulfate, but their sources and formation processes remain uncertain. In this study we characterize possible sources and formation processes of atmospheric sulfate by analyzing sulfur isotope abundances ( 32 S, 33 S, 34 S, and 36 S) and by detailed X‐ray diffraction and scanning electron microscope (SEM) imaging of aerosol samples acquired at a rural site in northern China from March to August 2005. The comparison of SEM images from coal fly ash and the atmospheric aerosols suggests that direct emission from coal combustion is a substantial source of primary atmospheric sulfate in the form of CaSO 4 . Airborne gypsum (CaSO 4 ·2H 2 O) is usually attributed to eolian dust or atmospheric reactions with H 2 SO 4 . SEM imaging also reveals mineral particles with soot aggregates adhered to the surface where they could decrease the single scattering albedo of these aerosols. In summer months, heterogeneous oxidation of SO 2 , derived from coal combustion, appears to be the dominant source of atmospheric sulfate. Our analyses of aerosol sulfate show a seasonal variation in Δ 33 S (Δ 33 S describes either a 33 S excess or depletion relative to that predicted from consideration of classical mass‐dependent isotope effects). Similar sulfur isotope variations have been observed in other atmospheric samples and in (homogenous) gas‐phase reactions. On the basis of atmospheric sounding and satellite data as well as a possible relationship between Δ 33 S and Convective Available Potential Energy (CAPE) during the sampling period, we attribute the sulfur isotope anomalies (Δ 33 S and Δ 36 S) in Xianghe aerosol sulfates to another atmospheric source (upper troposphere or lower stratosphere).Keywords:
Sulfate aerosol
Abstract. The sulfur cycle and radiative effects of sulfate aerosol on climate are studied with a Global tropospheric Climate-Chemistry Model in which chemistry, radiation and dynamics are fully coupled. Production and removal mechanisms of sulfate are analyzed for the conditions of natural and anthropogenic sulfur emissions. Results show that the 1985 anthropogenic emission tripled the global SO2 and sulfate loadings from its natural value of 0.16 and 0.10 Tg S, respectively. Under natural conditions, the fraction of sulfate produced in-cloud is 74%; whereas with anthropogenic emissions, the fraction of in-cloud sulfate production slightly increased to 76%. Lifetimes of SO2 and sulfate under polluted conditions are estimated to be 1.7 and 2.0 days, respectively. The tripling of sulfate results in a direct radiative forcing of −0.43 W m−2 (clear-sky) or −0.24 W m−2 (all-sky), and a significant first indirect forcing of −1.85 W m−2, leading to a mean global cooling of about 0.1 K. Regional forcing and responses are significantly stronger than the global values. The first indirect forcing is sensitive to the relationship between aerosol concentration and cloud droplet number concentration which requires further investigation. Two aspects of chemistry-climate interaction are addressed. Firstly, the coupling effects lead to a slight decrease of 1% in global sulfate loading for both the cases of natural and anthropogenic added sulfur emissions. Secondly, only the indirect effect of sulfate aerosols yields significantly stronger signals in changes of near surface temperature and sulfate loading than changes due to intrinsic climate variability, while other responses to the indirect effect and all responses to the direct effect are below noise level.
Sulfate aerosol
Sulfur Cycle
Forcing (mathematics)
Cite
Citations (25)
Abstract Natural aerosols play a central role in the Earth system. The conversion of dimethyl sulfide to sulfuric acid is the dominant source of oceanic secondary aerosol. Ocean emitted iodine can also produce aerosol. Using a GEOS‐Chem model, we present a simulation of iodine aerosol. The simulation compares well with the limited observational data set. Iodine aerosol concentrations are highest in the tropical marine boundary layer (MBL) averaging 5.2 ng (I) m −3 with monthly maximum concentrations of 90 ng (I) m −3 . These masses are small compared to sulfate (0.75% of MBL burden, up to 11% regionally) but are more significant compared to dimethyl sulfide sourced sulfate (3% of the MBL burden, up to 101% regionally). In the preindustrial, iodine aerosol makes up 0.88% of the MBL burden sulfate mass and regionally up to 21%. Iodine aerosol may be an important regional mechanism for ocean‐atmosphere interaction.
Dimethyl sulfide
Sulfate aerosol
Cite
Citations (27)
The IMPACT global chemistry and transport model has been updated to include an aerosol dynamics module. Here it is used to simulate the dynamics of sulfate aerosol and its interaction with nonsulfate aerosol components: carbonaceous aerosol (organic matter (OM) and black carbon (BC)), dust, and sea salt. The sulfate aerosol dynamics is based on the method of modes and moments. In the current implementation, two modes are used for sulfate aerosol (nuclei and accumulation mode), and two moments are predicted within each mode (sulfate aerosol number and mass concentration). The aging of carbonaceous aerosol and dust particles from hydrophobic to hydrophilic depends on the surface coating of sulfate which occurs as a result of the condensation of sulfuric acid gas H 2 SO 4 (g) on their surface, and coagulation with pure sulfate aerosol. The model predicts high sulfate aerosol number concentrations in the nuclei mode (over 10 4 cm −3 ) in the tropical upper troposphere, while accumulation mode sulfate number concentrations are generally within 50–500 cm −3 in most parts of the free troposphere. The model predicted mass concentrations of sulfate, OM, BC, dust, and sea salt, H 2 SO 4 (g) concentration, aerosol number, and size distributions are compared with measurement data. Our model predicts ∼80% of global sulfate existing as a pure sulfate aerosol (9.7% in nuclei and 69.8% in accumulation mode), with 14.3% on carbonaceous aerosol, 3.3% on dust, and 2.7% on sea salt. In the boundary layer, over 40% of sulfate is associated with nonsulfate aerosols in many regions of the world whereas less than 10% of sulfate is associated with nonsulfate aerosols in the upper troposphere. The model predicted mass fraction of sulfate in the sulfate‐carbonaceous aerosol mixture suggests that carbonaceous aerosol in most of the troposphere is internally mixed with sulfate and thus generally hygroscopic except near the source regions where the mass fraction is less than 5%. On the global mean, 54% and 93% of carbonaceous aerosol are coated with sulfate in the boundary layer and in the upper troposphere, respectively. Our result suggests that carbonaceous aerosols have a shorter lifetime (3∼4 days) than predicted (4∼8 days) using models that treat these aerosols as partly hydrophobic with an arbitrary e ‐folding time from hydrophobic to hydrophilic.
Sulfate aerosol
Sea salt aerosol
Cite
Citations (262)
Abstract. Air quality models have not been able to reproduce the magnitude of the observed concentrations of fine particulate matter (PM2.5) during wintertime Chinese haze events. The discrepancy has been at least partly attributed to low biases in modeled sulfate production rates, due to the lack of heterogeneous sulfate production on aerosols in the models. In this study, we explicitly implement four heterogeneous sulfate formation mechanisms into a regional chemical transport model, in addition to gas-phase and in-cloud sulfate production. We compare the model results with observations of sulfate concentrations and oxygen isotopes, Δ17O(SO42-), in the winter of 2014–2015, the latter of which is highly sensitive to the relative importance of different sulfate production mechanisms. Model results suggest that heterogeneous sulfate production on aerosols accounts for about 20 % of sulfate production in clean and polluted conditions, partially reducing the modeled low bias in sulfate concentrations. Model sensitivity studies in comparison with the Δ17O(SO42-) observations suggest that heterogeneous sulfate formation is dominated by transition metal ion-catalyzed oxidation of SO2.
Haze
Sulfate aerosol
Ammonium sulfate
Chemical Transport Model
Cite
Citations (199)
Sulfate aerosol
Sulfur Cycle
Cite
Citations (12)
Our laboratory experiments reveal a decrease in light backscattering by reactive uptake of isoprene epoxydiols on sulfate aerosol compared with inorganic sulfate, which can aid in quantifying the direct forcing of organic/inorganic sulfates.
Isoprene
Sulfate aerosol
Forcing (mathematics)
Cite
Citations (7)
Abstract. The sulfur cycle and radiative effects of sulfate aerosol on climate are studied with a Global tropospheric Climate-Chemistry Model in which chemistry, radiation and dynamics are fully coupled. Production and removal mechanisms of sulfate are analyzed for the conditions of natural and anthropogenic sulfur emissions. Results show that the 1985 anthropogenic emission doubled the global SO2 and sulfate loadings from its natural value of 0.15 and 0.27 Tg S, respectively. Under natural conditions, the fraction of sulfate produced in-cloud is 87%, and the lifetime of SO2 and sulfate are 1.8 and 4.0 days, respectively; whereas with anthropogenic emissions, changes in in-cloud sulfate production are small, while SO2 and sulfate lifetimes are significant reduced (1.0 and 2.4 days, respectively). The doubling of sulfate results in a direct radiative forcing of −0.32 and −0.14 W m−2 under clear-sky and all-sky conditions, respectively, and a significant first indirect forcing of −1.69 W m−2. The first indirect forcing is sensitive to the relationship between aerosol concentration and cloud droplet number concentration. Two aspects of chemistry-climate interaction are addressed. Firstly, the coupling effects lead to 10% and 2% decreases in sulfate loading, respectively, for the cases of natural and anthropogenic added sulfur emissions. Secondly, only the indirect effect of sulfate aerosols yields significantly stronger signals in changes of near surface temperature and sulfate loading than changes due to intrinsic climate variability, while other responses to the indirect effect and all responses to the direct effect are weak.
Sulfate aerosol
Sulfur Cycle
Forcing (mathematics)
Cite
Citations (0)
Anthropogenic SO(2) emissions may exert a significant cooling effect on climate in the Northern Hemisphere through backscattering of solar radiation by sulfate particles. Earlier estimates of the sulfate climate forcing were based on a limited number of sulfate-scattering correlation measurements from which a high sulfate-scattering efficiency was derived. Model results suggest that cloud processing of air is the underlying mechanism. Aqueous phase oxidation of SO(2) into sulfate and the subsequent release of the dry aerosol by cloud evaporation render sulfate a much more efficient scatterer than through gas-phase SO(2) oxidation.
Sulfate aerosol
Cloud albedo
Cite
Citations (203)
Abstract. The formation of new sulfate aerosol from the gas phase is commonly represented in atmospheric modeling with parameterizations of the steady state nucleation rate. Such parameterizations are based on classical nucleation theory or on aerosol nucleation rate tables, calculated with a numerical aerosol model. These parameterizations reproduce aerosol nucleation rates calculated with a numerical aerosol model only imprecisely. Additional errors can arise when the nucleation rate is used as a surrogate for the production rate of particles of a given size. We discuss these errors and present a method which allows a more precise calculation of steady state sulfate aerosol formation rates. The method is based on the semi-analytical solution of an aerosol system in steady state and on parameterized rate coefficients for H2SO4 uptake and loss by sulfate aerosol particles, calculated from laboratory and theoretical thermodynamic data.
Sulfate aerosol
Cite
Citations (3)
Abstract. The global source–receptor relationships of sulfate concentrations, and direct and indirect radiative forcing (DRF and IRF) from 16 regions/sectors for years 2010–2014 are examined in this study through utilizing a sulfur source-tagging capability implemented in the Community Earth System Model (CESM) with winds nudged to reanalysis data. Sulfate concentrations are mostly contributed by local emissions in regions with high emissions, while over regions with relatively low SO2 emissions, the near-surface sulfate concentrations are primarily attributed to non-local sources from long-range transport. Regional source efficiencies of sulfate concentrations are higher over regions with dry atmospheric conditions and less export, suggesting that lifetime of aerosols, together with regional export, is important in determining regional air quality. The simulated global total sulfate DRF is −0.42 W m−2, with −0.31 W m−2 contributed by anthropogenic sulfate and −0.11 W m−2 contributed by natural sulfate, relative to a state with no sulfur emissions. In the Southern Hemisphere tropics, dimethyl sulfide (DMS) contributes 17–84 % to the total DRF. East Asia has the largest contribution of 20–30 % over the Northern Hemisphere mid- and high latitudes. A 20 % perturbation of sulfate and its precursor emissions gives a sulfate incremental IRF of −0.44 W m−2. DMS has the largest contribution, explaining −0.23 W m−2 of the global sulfate incremental IRF. Incremental IRF over regions in the Southern Hemisphere with low background aerosols is more sensitive to emission perturbation than that over the polluted Northern Hemisphere.
Sulfate aerosol
Sulfur Cycle
Carbonyl sulfide
Dimethyl sulfide
Chemical Transport Model
Cite
Citations (99)