Section highlights

Organic Aerosol and Field Studies

• Measurement techniques– Artifact free sampling– Size resolved sampling– BC/OC/WSOC link to chemical composition– Individual component chemical speciation– Functional group analysis

• Mass Balance– OC to OM conversion– Water content

• Biogenic vs anthropogenic• Primary vs secondary

– Sources– precursors

How much OA is there?

Interactions among OA and other aerosol species

• Size distributions

• Mixing state in individual particles

• Solid/liquid

• Changes with aging

Measurement techniques :OC/BC• The EMEP EC/OC measurement campaign

provides data from June 2002-June 2003 from 13 European countries.

• High variability of OC (as C) mass concentration.• EC mass concentration on average roughly 5% of

PM10 mass. Less variable.

• OC speciation is needed to determine correction factors, improve models and to assist the data interpretation.

• OC speciation strategy should be implemented.» Dye

• Large possibly systematic errors can occur in the determination of Particulate Organic Matter concentrations at several steps:

• sampling artifacts can be huge• OC/EC analyses affcted by:

– OC/EC split definition– charring– optical corrections (TOT vs. TOR) not always consistent– OC -> OM conversion factor (namely 1.4) quite uncertain

• if random uncertainties are small enough, mass closure exercises can constrain the systematic errrors in POM determination. Mass closure attempts are highly recommended

• (Putaud)

• HNMR allows to characterize aerosol WSOC : It provides an average composition which accounts for all the WSOC mixture (all compounds carrying C-H bonds);

• functional groups composition can be used to obtain information on possible sources/transformations of WSOC (e.g., B.B.), but HNMR source profiles (for primary and secondary sources) are needed;

• The budget of functional groups can be used to formulate model compounds and to validating models of SOA formation

Functional group analysis

BIOMASS BURNING AEROSOL

• Most of the PM is organic

• Ca 50% is WSOC

• Organic speciation will be available soon

• Amazon is an excellent lab. for the study of OA and their properties

Biogenic vs anthropogenicPrimary vs secondary

• A new tool for elucidating SOA formation :a novel sampling device minimizing artifacts was used to study in situ gas/particle patitioning of primary and secondary aersosol components

• Formation of organic solutions by the primary and secondary organics lowers the saturation conc. of photo-oxidation products facilitating new particle formation

Organic marine aerosol• Organic species represent the most abundant fraction of

aerosol mass in the size d< 0.5 mm (55-84%). • Organic fraction is dominated by water insoluble

compounds WIOC/TC• WSOC concentration is comparable to nss-SO4 in the

fine size range• WSOC analysis and surface tension measurements

show the presence of humic substances and in general indicate that OM has an hydrophobic character

• OA marine primary source?• Marine CCN

Amazonian basin and SOA

• Lack of nucleation events despite the availability of biogenic SOA precursors– Good test for global aerosol modelling– Excellent data set for CCN closure

measurements

Optical properties

• Optical property measurements as a function of wavelength– Laboratory and field : closure study– Brown carbon- HULIS– Mixing with black carbon

• Changes with aging

• The observed differences between the absorption index of water and the fog samples from the Po Valley have negligible effects in the reduction of the single scattering albedo of clouds and fog droplets.

• The Single Scattering Albedo of fog and clouds can be treated as pure scattering particles in radiation calculations similar to pure water, even in polluted regions like the Po Valley.

• Selected Organic acids in WSOC have pure scattering effects. They scatter solar radiation in a similar manner as sulphate aerosols and they have the same cooling effect on the climate.

• AMAZONIAN BASIN: Single scattering albedo surprisingly high (0.92) Significantly less absorption than assumed in the past

Hygroscopic growth and CCN ability

• Size resolved closure studies:– WSOC/TC, – OC speciation and – hygroscopic growth measurements– CCN measurements

• Changes with aging

• EMEP: new data set on WSOC soon

• Marine aersosol and CCN properties: role of WSOC and insoluble OA

• Surface tension depression due to organics : the role of HULIS

• Biomass burning aersosol: WSOC/TC ca. 50%

• Functional group analysis as a tool to gain information on Hygroscopic/hydrophobic OA character