Particulate Matter (PM) Overview 4 February 2015 Rob Griffin (rob.griffin@rice.edu)

Who Am I and What Do I Do? I’m a professor in CEVE (despite doing all my degrees in CHE) at Rice in Houston

Who Am I and What Do I Do? Research focuses on what happens to things once they get to the atmosphere – lab-based experiments, measurements in the ambient atmosphere, and computer modeling to describe air quality (often with Dr. Dabdub)

What is an Aerosol? Metastable suspension of particles in a background gas Solid or liquid, generally assumed to be spherical For our interests, the background gas is air Metastable? Stable enough to persist within a time frame of interest Rain? Too short – falls too rapidly (within hours) Infinity? Too long Generally – atmospheric lifetime of ~1 week Aerosol = gas + particles Particulate matter (PM) = just the particles

So How Big Are We Talking? N ~ 103 -104 cm-3 More in polluted Less in remote Particle surface area distribution * This cutoff sometimes defined as 1 mm

Why Do We Even Care About PM? Heterogeneous Reaction Site Reflectance Reflectance Cloud Formation Aerosol Layer Deposition Precipitation Inhalation Visibility Degradation Absorption

NAAQS Primary standard – Designed to protect human health, particularly that of sensitive groups Secondary standard – Designed to protect public welfare (visibility; damage to animals, crops, vegetation, and buildings) Criteria pollutants: CO, NO2, O3, Pb, SO2, PM2.5, PM10 PM2.5 primary annual average 12 mg m-3; secondary annual average 15 mg m-3; primary and secondary daily average 35 mg m-3 PM10 primary and secondary: 24-hour 150 mg m-3

Transport and Deposition Trans-Atlantic dust transport followed by deposition to the Caribbean has been implicated in coral death (due to microbes) Other examples: Deposited particles clogging stomata, nutrient cycling, acidification of soil, destruction of artwork

Visibility Other examples?

Reaction Sites Aerosols are a heterogeneous source of X in the stratosphere

Climate Impacts Note level of scientific understanding (IPCC)

Emitted vs. Formed Primary Secondary Gas A Gas B

Most Abundant Aerosol Components IDEAS?

Most Abundant Aerosol Components Water Sulfate Nitrate Ammonium Organics Carbonates Elemental/black carbon Sodium Chloride Crustal/Minerals (Dust) Metals

Global Aerosol Sources Notes Issues Amount (Tg/yr) Soil dust Wind driven in drier climates; composition varies regionally Microbes, “dust storms” 1500 Sea salt Wind/wave driven; dominated by NaCl Displacement 10000 Volcanic debris Composition varies regionally Secondary chemistry 30 Biological debris Wind driven; mostly organic Hard to ID 50 Anthropogenic primary aerosol Linked to combustion; many constituents Region/source dependence 200 Secondary sulfate Sulfur + oxidant Very non-volatile 50 anth. SO2; 10 DMS; 20 volc. SO2 Secondary nitrate Nitrogen + oxidant Size depends on formation route 20 anth; ? natural SOA VOC + oxidant 10 anth.; ~15 biogenic

Aerosol Field Measurements What parameters matter?

Aerosol Field Measurements What parameters matter? How much is there? What is it made of? How many particles are there? How big are they? What are their physical properties? Others…

Aerosol Field Measurements How much is there? Filter-based (pull air through it, weight it before and after) or similar methods Composition-based (sum up all the stuff you identify) Size-based (count how many particles you have of a certain size, use geometry and an assumed density)

Aerosol Field Measurements What is it made of? Off-line chemical analytical techniques: You name it, it has probably been done (requires filter extracts or collection of PM into water sample using a PILS or other collection technique) On-line chemical techniques: State-of-science = aerosol mass spectrometry (AMS) Physical characterization: If it is black (determined by light measurement), it’s almost exclusively black carbon (aethalometer)

Aerosol Field Measurements How many particles are there? Count them! Typically done using optics (for bigger particles) in an optical particle counter (OPC) or using lasers (for smaller particles) in a condensation nucleus counter (CNC)

Aerosol Field Measurements How big are they? Typically done by applying an external force and seeing how the particle responds (force balance). For example, a differential mobility analyzer (DMA) puts a charge on a particle and then exposes them to an electric field (voltage across a gap); based on the geometry and flow of the system only a particle of a given size exits the DMA (to then be detected by a CNC)

Aerosol Field Measurements What are their physical properties? Do they scatter light? A nephelometer determines this (think about visibility and climate forcing) - Shine light in one direction and measure it at a different angle Do they take up water? A tandem DMA determines this (think about visibility, climate forcing, chemistry…) - Pick one size particle with a DMA, expose the particles to increased RH, measure size with a second DMA

Aerosol Field Measurements This list could go on for a really, really long time As could the list of places where such measurements have been performed (surface-fixed, surface-mobile, airplane-based…)

Thanks… For your attention and participation Please don’t hesitate to contact me with questions about PM, field campaigns, Rice, Houston, etc.