Molecular Tracers Indicate Organic Aerosols In The Marine Boundary Layer And The History Of Penguin Colonies

Aerosols can affect climate directly by scattering and absorbing sunlight and indirectly acting as cloud condensation nuclei(CCN).The radiative forcing of aerosols is the largest source of uncertainty for climate projections.Lacking understanding of the concentration and chemical component of aerosols over oceans,especially over remote oceans contributes much to this uncertainty.Organic aerosols are important components of marine aerosols,especially submicron aerosols whose climate effect are significant.Via molecular tracers,this study traced secondary organic aerosols(SOAs)from isoprene and monoterpenes,biomass burning aerosols,mono-and dicarboxylic acids in the marine boundary layer along the cruises path during the 3rd Chinese Arctic Research Expedition(CHINARE 08)and the 26th Chinese Antarctic Research Expedition(CHINARE 09/10).We investigated the species,concentration,sources and influencing factors of organic aerosols,and also researched volatile organic compounds(VOCs)as the precursors for SOAs.This study is in favor for a more comprehensive understanding of organic aerosols over oceans.Besides,organic molecular tracers were also applied in the research of palaeoenvironment and paleoecology in this dissertation,and were used to reconstruct the history of penguin and associated plants in the Ross Sea region,high Antarctic.The major contents and results in this dissertation are listed below.1.Isoprene and monoterpene SOA tracers were detected over all seas from the Arctic and the Antarctic.The sums of isoprene SOA tracers varied from 0.018 to 36 ng m-3,with a mean of 8.5±11 ng m-3;while the sum of monoterpene SOA tracers varied from 0.045 to 20 ng m-3,with an average of 3.0±5.0 ng m-3.The average values in the Northern Hemisphere were approximately one order of magnitude higher than those in the Southern Hemisphere.Affected by the input from continents,SOA tracers from isoprene and monoterpene over coastal regions were in high levels.However,SOA tracers over remote oceans were only derived from oceanic sources,and thus were in low levels.However,isoprene SOA from marine source may abruptly increase and significantly affect marine SOAs during phytoplankton blooms.2.Via levoglucosan,the tracer for biomass burning aerosols,we found the ubiquitous influence of biomass burning on aerosols in the marine boundary layer.The concentrations of levoglucosan in samples collected during the CHINARE 08 and the CHINARE 09/10 varied from 0.18 to 41 ng m-3,with a mean of 5.4±6.2 ng m-3.Spatial variation of levoglucosan concentrations were obvious.But as a whole,levoglucosan concentrations in the Southern Hemisphere were comparable to those in the Northern Hemisphere.Levoglucosan was found to be present in all regions with the highest atmospheric loadings present in the mid-latitudes(30°-60° N and S),intermediate loadings in the high latitudes of the Northern Hemisphere(60°-90° N),and lowest loadings in the Antarctic and equatorial latitudes.Biomass burning had a significant impact on atmospheric mercury(Hg)and water-soluble organic carbon(WSOC)from pole-to-pole,with more contribution to WSOC in the Northern Hemisphere than in the Southern Hemisphere.Furthermore,biomass burning may be a potential source for organic carbon in snow in continental Antarctica.3.The sums of monocarboxylic acid(C14:0-C32:0,C16:1,C18:1 and C18:2)varied from 2.9 to 54 ng m-3,with a mean of 19±16 ng m-3 in aerosol samples collected during the CHINARE 08.Dicarboxylic acid(di-C4-di-C10)concentrations varied from 6.0 to 483 ng m-3,with a mean of 239±123 ng m-3.The peak of saturated monocarboxylic acids was present in C 16:0,followed by C18:0 and C 14:0.The concentrations of unsaturated monocarboxylic acids were much lower than those of saturated monocarboxylic acids,with the peak in C18:1.By and large,the concentrations of each dicarboxylic acid decreased with increasing number of carbon atoms,with the peaks in di-C4 and di-C5.Mono-and dicarboxylic acid concentrations decreased in general with increasing latitudes,with significantly higher levels south of the Arctic Circle than those north of the Arctic Circle.The sources of mono-and dicarboxylic acids included biomass burning emissions,primary emissions from oceans,formation through photochemical reactions,anthropogenic emissions and emissions by terrestrial plants.4.WSOC in samples collected during the CHINARE 08 and CHINARE 09/10 varied from 86 to 3850 ng/m3,with a mean of 859±673 ng m-3.Isoprene SOA,monoterpene SOA,biomass burning aerosols and dicarboxylic acids were all components of WSOC,and averagely contributed 7.2±8.9%,1.9±2.9%,7.6±7.5%and 20±14%to WSOC,respectively.5.Via indictor carbon monoxide(CO),this study found that fossil fuel combustion may be an ignored source for ?-pinene,?-pinene and CH3I.Without samples obviously polluted by emissions from the ship,the average concentrations in samples collected during the 28th Chinese Antarctic Research Expedition(CHINARE 11/12)and the 5rd Chinese Arctic Research Expedition(CHINARE 12)were 40±67,61±246 and 29±90 pptv for isoprene,a-pinene and ?-pinene,respectively.Spatial variations of the three VOCs were obvious,with the lowest median levels in middle and high latitudes of the Northern Hemisphere.Isoprene and monoterpenes(a-pinene and ?-pinene)are important precursors for SOA.However,due to the influence of continents on SOA over oceans,the spatial variations of SOAs were not similar with their precursors.However,when the impact from continents was negligible,they showed similar trend.For example,the concentrations of both isoprene and its SOA significantly increased in the Prydz Bay,Antarctic during phytoplankton blooms.6.Without samples obviously polluted by emissions from the ship,CH3I concentrations in the marine boundary layer during the CHINARE 11/12 and the CHINARE 12 varied from 0.17 to 4.8 pptv,with a mean of 0.60±0.57 pptv.The levels of CH3I in the Northern Hemisphere were significantly higher than those in the Southern Hemisphere,with the highest levels in the middle latitudes of the Northern Hemisphere and the lowest levels in the high latitudes of the Southern Hemisphere.CH3I concentrations were affected by sea surface chlorophyll-a,dissolved organic carbon,temperature as well as fossil fuel and biomass burning and wind speed.Besides,organic iodine is an important component of organic aerosols.Via analysis by Orbitrap mass selective detector(MS),we found that hexane iodide(C6H13I)may be a component of organic iodine.However,it is need further confirmed.7.Penguins are an important seabird species in Antarctica and are sensitive to climate and environmental changes.Through molecular tracers in a sediment profile collected along the northwest beach of Cape Bird,Ross Island,Antarctica,the history of penguins,seals and surrounding plants in the past 700 years was reconstructed.The region transformed from a seal to a penguin habitat when the Little Ice Age(LIA,1500-1800 AD)began.The activity of penguins was advantageous for the growth of algae,but disadvantageous for the growth of lichens.Penguin populations were the highest during ca.1490 to 1670 AD,a cold period,which is contrary to previous results in other regions much farther north where penguin populations increased when the climate became warmer and decreased when it became colder.The increasing polynya in the Ross Sea region during LIA and emigrations of penguins to the sampling site may caused the increased penguin population during the cold period.This study suggested that different responses to climate change may occur in different regions,even if for same species.