Dalhousie University Department of Physics and Atmospheric Science

Dalhousie University Department of Physics and Atmospheric Science Research in Theoretical, Experimental, and Applied Physics • Materials Science • Biophysics • Condensed Matter Physics • Atmospheric Science http: //www. physics. dal. ca/files/Physics_and_Atmospheric_Science_Faculty. ppt

Ozone and Aerosols in the Lower Atmosphere Randall Martin Aaron Van Donkelaar Kelly Chance Chris Sioris Arlene Fiore

GLOBAL RADIATIVE FORCING OF CLIMATE, 1750 -present IPCC [2001]

ORIGIN OF ATMOSPHERIC AEROSOLS Aerosol: dispersed condensed matter suspended in a gas Size range: 0. 001 mm (molecular cluster) to 100 mm (small raindrop) Soil dust Sea salt Environmental importance: health (respiration), visibility, radiative balance, cloud formation, heterogeneous reactions, delivery of nutrients…

COMPOSITION OF PM 2. 5 (NARSTO PM ASSESSMENT)

Scattering of Radiation Size Parameter: x= 2 pr/l

Mie Theory Extinction = Scattering + Absorption Extinction Efficiency (Qext) = ratio of the extinction cross section to the geometric cross-section (πr 2)

MODerate-resolution Imaging Spectroradiometer (MODIS) Seven MODIS bands are available for aerosol properties 0. 47, 0. 55, 0. 65, 0. 86, 1. 24, 1. 64, and 2. 13 µm OCEAN reflectance contrast between cloud-free atmosphere and dark ocean aerosol optical thickness for all 7 bands LAND reflectance of dark vegetation and semi-arid regions deduced using 2. 13 µm where aerosols are nearly transparent reflectance contrast between atmosphere and dense dark vegetation surface aerosol optical thickness (0. 47 and 0. 66 µm) Optical Thickness I=Ioe-

What do we actually see?

Aerosols Visible over Dark Surface Mar 3, 2003

Example Cloud and Aerosol Optical Thickness (550 nm) Cloud Optical Thickness

TROPOSPHERIC OZONE IS A KEY SPECIES IN CLIMATE AND AIR QUALITY • Major greenhouse gas Mesosphere Stratopause Ozone layer • Primary constituent of smog • Largely controls atmospheric oxidation Stratosphere Tropopause Troposphere

THE ATMOSPHERE IS AN OXIDIZING MEDIUM Oxidation Reduced gas EARTH SURFACE Oxidized gas/ aerosol Uptake Emission Reduction

Simplified Tropospheric Ozone (O 3) Chemistry hv O 3 hv, H 2 O OH NO 2 NOx NO OH HOx HO 2 HNO 3 H 2 O 2 CO, VOCs, NOx VOCs + OH HCHO Role of Formaldehyde (HCHO) HCHO + h 2 HO 2 + CO HCHO + OH HO 2 + CO + H 2 O

THE NITROGEN CYCLE: MAJOR PROCESSES ATMOSPHERE N 2 combustion lightning NO oxidation HNO 3 biofixation org. N BIOSPHERE burial LITHOSPHERE denitrification deposition decay assimilation NH 3/NH 4+ nitrification NO 3 weathering

NOx EMISSIONS (Tg N yr-1) TO TROPOSPHERE LIGHTNING 6 STRATOSPHERE 0. 2 SOILS 5 BIOMASS BURNING BIOFUEL 5 AIRCRAFT 2 0. 5 FOSSIL FUEL 20

EULERIAN RESEARCH MODELS SOLVE MASS BALANCE (alias CONTINUITY) EQUATION IN 3 -D ASSEMBLAGE OF GRIDBOXES Solve continuity equation for individual gridboxes • Models can presently afford ~ 106 gridboxes • In global models, this implies a horizontal resolution of 100 -500 km in horizontal and ~ 1 km in vertical

BOTTOM-UP EMISSION INVENTORIES ARE NOTORIOUSLY DIFFICULT TO DETERMINE • • • Fuel use estimates Measurements of emission ratios Process studies Estimate biological density Temperature, water, … dependence of biological activity • Extreme events

Absorbing properties of molecules Atmospheric trace gas absorptions detected in satellite spectra:

Retrieval of Trace Gas Column Nonlinear least-squares fitting Solar Io Backscattered intensity IB Scattering by Earth surface and by atmosphere A EARTH SURFACE

Total NO 2 Slant Columns Observed from the SCIAMACHY Satellite Instrument May-August 2004

Perform a Radiative Transfer Calculation to Account for Viewing Geometry and Scattering Cloud Screening: Remove Scenes with IB, c > IB, o IB, c Io q • LIDORT Radiative Transfer Model [Spurr et al. , 2002] • FRESCO Clouds Fields [Koelemeijer et al. , 2002] Ro • GOME Surface Reflectivity [Koelemeijer et al. , 2003] Rc Pc dt Rs

Tropospheric NO 2 Columns Observed from the SCIAMACHY Satellite Instrument May-August 2004 detection limit

Major Urban Centers Are Concentrated NOx Sources May-August 2004 detection limit

Ozone Control Strategies Require Independent Information on Effectiveness of Reducing NOx or VOCs Shown that the HCHO/NO 2 Ratio Is as Indicator That Can be Observed from Space (ppbv) NOx-Saturated NOx-Limited Sillman and He, 2002

GOME Observations Show NOx-Sensitive Conditions Over Most Polluted Regions During August Major Industrial Areas are Clear Exceptions White areas indicate clouds or data below the GOME detection limit August

Biomass Burning Emissions are Clearly NOx-Sensitive, In Contrast with NOx-Saturated Conditions Over the Industrial Highveld Also observe plume evolution August NOx Lim

Seasonal Evolution from NOx-Sensitive to NOx-Saturated Conditions in Fall