particulate matter (pm) overview 4 february 2015 rob griffin ([email protected])
TRANSCRIPT
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 longGenerally – atmospheric lifetime of ~1 week
Aerosol = gas + particlesParticulate matter (PM) = just the particles
So How Big Are We Talking?
* This cutoff sometimes defined as 1 m
N ~ 103 -104 cm-3
More in pollutedLess in remote
Particle surface area distribution
Why Do We Even Care About PM?
Aerosol Layer CloudFormation
Deposition
InhalationVisibilityDegradation
Reflectance
Precipitation
HeterogeneousReaction Site
Ab
sorp
tion
Reflectance
NAAQSPrimary 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 g m-3; secondary annual average 15 g m-3; primary and secondary daily average 35 g m-3
PM10 primary and secondary: 24-hour 150 g 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. FormedPrimary Secondary
Gas A Gas B
Most Abundant Aerosol Components
IDEAS?
Most Abundant Aerosol Components
WaterSulfateNitrateAmmoniumOrganicsCarbonatesElemental/black carbonSodiumChlorideCrustal/Minerals (Dust)Metals
Global Aerosol SourcesSource 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 Hard to ID 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.