Satellite-based Estimates Of Global Emissions Of Marine Trace Gases And Aerosols

The oceans cover 71% of the Earth's surface area and represent a major emissions source of many trace gases and aerosols that influence atmospheric chemistry and climate.Despite a large body of pioneering research on marine emissions and their environmental and climatic effects,a global inventory of trace gases and aerosols emissions from the ocean is still lack,introducing a large uncertainty in global simulations of the Earth system.Here we used remote sensing data products derived from ocean observing satellites to quantify global emissions major trace gases and particulate matter from the oceans.Next,the similarities and differences of the results obtained through different methods were compared and analyzed,so that a high-resolution inventory of global marine emission could be used for modeling research.Finally,we apply the newly developed marine isoprene emission to study the effects on ozone and SOA concentration in the eastern coastal areas of China.The main findings from this study include:?1?We firstly developed a new method to calculate emission flux of marine isoprene from sea surface microlayer?SML?by using remotely sensed particulate organic carbon?POC?and primary productivity.The estimated isoprene emission from SML is 1.07 Tg C/yr.The estimated emission is comparable to the observed data,slightly higher than the emissions calculated by satellite chlorophyll-a concentration,but lower than the values derived from mesocosm experiments and isoprene SOA products.The results are similar to that from an earlier study using a different method.Adding this to the chlorophyll-based isoprene emissions,the total annual global isoprene emissions were 1.16?5.47 Tg C/yr.Comparing to the results estimated by“top-down”method?1.69 and 11.6 Tg C/yr?,this new source effectively reduces the gap between the“bottom-up”and“top-down”emissions.?2?The marine DMS concentrations calculated by three empirical formulas revealed large variations in their spatial distributions and values.In general,the DMS concentration estimated with the CJQ method had higher values in the open ocean,there was no excessive calculated value,and the formula considered more effect factors than the other two.The estimates of the Chl/MLD method reported too many outliers.The DMSP method had better convergence of calculated values,but the estimated values were lower and showed weak variability in spatial distribution.High DMS fluxes mainly appeared in the vicinity of several high wind belts,as well as in the middle and low latitudes of the coasts and the Arabian Sea in June and July with values up to 10?M/?m²·d?.In contrast,the fluxes in the low wind speed belts were usually below 2?M/?m²·d?.Total annual DMS emissions calculated by these three empirical methods were17.83,19.57 and 11.12 Tg S/yr,respectively.?3?According to the existed parameterization method,we established an effect factor term including three variables,chlorophyll-a,Sea surface temperature?SST?and Photosynthetic available radiation?PAR?,which had higher correlation than single variable,and the linear relationships between CHBr₃ and other halocarbon species.Then estimated the emissions of nine halocarbon speices?CHBr₃,CH₂Br₂,CH₂BrCl,CHBr₂Cl,CHBrCl₂,CH₂ClI,CH₂BrI,CH₂I₂ and CH₃I?.The global oceanic CHBr₃showed a high emission flux in the equatorial region,and generally decreased from low latitude to two poles and from coasts to open oceans.The spatio-temporal distributions and variabilities at middle and high latitudes were influenced by meridional variation of solar radiation.Seasonal variations of CHBr₃ flux were more pronounced in the northern hemisphere than in the southern hemisphere.The global monthly CHBr₃ flux varied between 10⁶ and 10⁷ molecules/?cm²·s?,with an annual average of 1.60×10⁷molecules/?cm²·s?and emission of 736.48 Gg/yr.?4?Global Primary Organic Aerosols?POA?was quantified by using four Sea salt aerosol?SSA?source formulae?C06,O14,S15 and G03-J11?.The results showed that the global POA flux presented spatial pattern of belt distribution which was similar to that of the wind field.High fluxes appeared in the areas on both sides of the equator and the mid-high latitude,which were several times larger than the surrounding areas.In comparison,POA fluxes in high and mid-low latitude were smaller because of the lower wind speed and chlorophyll concentration.Among these four methods,C06 had the highest POA flux,followed by S15 and G03-J11,and O14 was the lowest.Furthermore,the calculated POA was generally underestimated comparing to observations,with larger discrepancy in coastal areas and the North Atlantic and better performance in open ocean.The monthly POA emissions were low in spring and autumn,while higher in summer and winter,and annual emissions calculated by G03,C06,O14 and S15 were 1.10,4.01,0.92 and 1.90 Tg,respectively.?5?Model simulations showed that SML emissions can contribute up to 0.02 ppb isoprene concentration over the eastern coast of China,with higher value appearing over the Bohai Sea and coastal areas.The diurnal variations of atmospheric isoprene concentration presented a bimodal pattern.Marine isoprene had little effect on the inland isoprene concentration,but it contributed 40-60%of isoprene in the coastal areas.Meanwhile,the contribution of marine isoprene to the O₃ in coastal urban areas was considered to be small?0.05?0.2%?with increased concentration up to 0.15 ppb,while its contribution to SOA was 20?30%with increased concentration up to 0.003?g/m³.