《大气环境化学》课件：aerosol-02

1、 大气气溶胶大气气溶胶的重要性n空气质量n人体健康n能见度n气候变化n云物理n大气辐射n中小尺度动力系统（城市气象）n大气化学ScatteringFormation of CCNAerosol and Visibility Aerosol and Visibility0.000.100.200.300.400.5010-16 10-18 10-20 10-22 10-24 10-26 10-28 10-3011-111-3datetotal mass of aerosol (mg/m3)0510152010-16 10-18 10-20 10-22 10-24 10-26 10-28 10-3

2、0 11-111-3datevisibility(km)气溶胶的物理化学特征n化学成分n空间分布n物理特征n气溶胶的形成化学成分nSulfate nNitratenBlack CarbonnOrganic Carbon POC and SOCnMineral DustnSea-salt垂直空间分布SO2 sulfateStratospheric Background aerosols nOCS (1 year lifetime) StratospherenOCS SO2nSO2 SulfatenBackground aerosols (1-2 ug/m3)nVolcanic aerosols

3、(20-50 ug/m3)对流层空间分布对流层空间分布物理特征n数浓度数浓度Nucleation modeAccumulation ModeCoarse Mode0.03 0.3 3um物理特征n质量浓度质量浓度Nucleation modeAccumulation ModeCoarse Mode0.03 0.3 3 Log-normal distribution Diameterln Dm = ln Dg + 3 N2gwhere Dm = mass weighted diameter Dg = geometric mean diameter Dm DgDgDm气溶胶的形成Sources o

4、f Particles: IndustrialBiomass BurningSea-saltDust气溶胶的形成气溶胶的形成nChemistrynNucleationnCondensationnCoagulationnHydrotropic growthnDepositionAqueous ChemistrynSO2 H2SO4n(1) Gas-phase (30-40%) SO2 + OH H2SO4n(2) Aqueous-phase (60-70%) SO2(a) + H2O2(a) H2SO4(a) SO2(a) + O3(a) H2SO4(a) NucleationnHomogene

5、ous NucleationnGas phase Particle phasenHeterogeneous NucleationnExisting small particles (direct emission)Homogeneous NucleationnPhase Transfer (Gas Particles)nGas vapor pressure P PsnPs = Saturation PressurenSulfate, SOCProblem in Homogeneous Nucleation TheoryNumber of particleVapor Pressure103The

6、oryMeasurementProgress on the problemn(1) Traditional theory P PsProgress on the problemn(1) NH3 effects P PsProgress on the problemn(1) NH3 effects (Ps decrease) P PsProgress on the problemn(1) Organic Acid effects (Ps decrease) P PsZhang et al., Science, 2004CondensationKs, kdCoagulationCoagulatio

7、n M = (i-1)Hydrotropic growthHydrotropic growthDRH 80Hydrotropic growthnChange the cross-section of scattering Hydrotropic growthnChange the absorption of aerosols DepositionnDry depositionnWet depositionDry depositionnThe flux (F) to the surface n nF = - Vd x C nVd = 1/(Ra + Rb + Rc)nRa is the aero

8、dynamic resistance (meteorological conditions) Rb is the quasi-laminar sub-layer resistance (kinetic viscosity of air) Rc is the total surface resistance (surface type)Wet depositionnRain frequency and strengthnSolubility (hydrophilic aerosol only)气溶胶大气化学 气溶胶大气化学nPhotolysis (J)nHeterogeneous reactio

9、nsTie et al., JGR 2005 Aerosols not onlyaffect climate, butalso chemistryPhotolysis rate JImportant Photolysis (J)n Ozone formation VOCs + OH RO2 RO2 + NO NO2 NO2 + hv NO + O (JNO2) O + O2 O3Important Photolysis (J)n OH formation O3 + hv O(1D) + O2 (JO3) O(1D) + H2O 2 OH Important Photolysis (J)n OH

10、 formation CH2O + hv H + HCO (JCH2O) H + O2 HO2 HO2 + NO OH + NO2Important Photolysis (J)n NOx in Remote region PAN + hv NO2 + Prod (JPAN) Important of PANTo transport NOx from source to remote region nPAN = CH3CO3NO2nCH3CO3 + NO2 PANnPAN + hv CH3CO3 + NO2 + CH3O2 + NO3Impact of aerosol on JJ(i)= F

11、x (i)(i)F = solar FluxImpact of aerosols on JScattering F0F1Impact of aerosols on JAbsorbF0F1AerosolsnSulfate ScatteringnNitrate ScatteringnOC Scattering (abs?)nSOC ScatteringnSea-salt ScatteringnDust Weak absorptionnEC Strong absorptionAerosol Parameters nAerosol optical depth (AOD)nAsymmetry param

12、eter (g)nSingle albedo ()Aerosol optical depthAsymmetry ParameterSingle AlbedoMODIS AODFactors to affect the impact ofAerosols on radiative forcingnMass of aerosol concentrations (AOD)nSize of aerosols (AOD, g)nComposition of aerosols (AOD, )nRH (AOD, , g)nShape of aerosols (AOD, , g)nThe vertical d

13、istribution of aerosolVertical distribution of scattering aerosolsVertical distribution of scattering aerosolsVertical distribution of absorption aerosolsVertical distribution of absorption aerosolsShape of aerosolsComposition of aerosolsnEC (soot) = 0.46 nSulfate = 1.0nH2O = 1.0PRD, 42.4 ug/m3Ammon

14、ium7%Sulfate25%unknown15%Nitrate4%EC6%OC31%Trace3%Crustal9%External Mixing of aerosols = Ai x Wi = 0.46*0.1 + 1.0*0.9 = 0.946 = 0.46*0.2 + 1.0*0.8 = 0.892Fine particle optical properties: light scattering and absorptionCollaboration with MPI and IFT, GermanyGuangzhou urban, 2004Internal Mixing of Ae

15、rosolsHeterogeneous ReactionsA B with (1)N2O5 + sulfate 2HNO3(1)N2O5 + sulfate 2HNO3(1)HO2 + sulfate ProductsNOx,CO, HCs, AerosolsEmissions 大气化学气溶胶模式NOx,CO, HCs, AerosolsMixingNight PBLMixing in low PBL during nightNOx,CO, HCs, AerosolsMixingDaytime PBLMixing in high PBL during dayNOx,CO, HCs, Aerosols