1. Composition determines size
The graph above also helps us to determine where are possible origins of suspended particulates in the ambient airs (PM2.5, PM10 or even PM100).
Uncoverred construction with a strong wind can sweep up fine sand and dust from construction sites. For construction, please look at the standard for PM100. NOx emitted from internal combustion or any high-temperature burning. Partitioning fertilizers to gaseous phase could provide nitrate and ammoniuum salts to the atmosphere. Burning high-sulfur fuel such as coals and diesel produce surfide dioxide, which is quickly converted to sulfate. More abundantly, combustions especially diesel engine emits carbon soots that contributes to the formation of fine (PM2.5) or untrafine particles. Gasoline engine produced more SOA (Secondary Organic Aerosol) than the primary PM. In the suitable condition, SOA could form 5 times particles than by the primary emission (Gordon at el. 2014).
2. Gravimetric method
This method simply means to measure the weight of a filter before and after a period of sampling, in which ambient air is drawn in by a pump with a pre-filtering apparatus to only select the target size of particulate matter.
The best resource I found is Notice 32/2013/TT-BTNMT by Vietnam MONRE on Issuance National Standards on Environment. The document constains 4 National Standards (QCVN). For PMs sampling method, look for QCVN O5:2013/BTNMT.
For PMs, here is a list of methods for sampling amd measuring:
- TCVN 5067:1995: Gravimetrics
- TCVN 9469:2012: Beta Attenuation Monitor
- AS/NZS 3580.9.6:2003, AS/NZS 3522.214.171.1249: Sampling methods for gravimetrics
2.2 United States
For the US, the concentration of PM2.5 is mandated by the Code of Federal Regulations by CFR § 50.7 which also provides a reference and a equipvalent methods.
- CFR §40 , appendix table E: Checklist for a protocol of reference method
- A list of designated reference and equivalent methods issued by US EPA (2016)
- Another list for Federal Refernece Method (FRM)
- Method 201A: Determination of PM10 and PM2.5 Emissions from Stationary Sources by US EPA
3. Mass and mass equipvalent
3.1 Tapered Oscillating Microbalance (TOEM®)
The mass of particles collected into a filterr results in change of oscillating mass and hence, the oscillating frequency. If we know the frequency and mass at time zero and the time t, using gravimetric method to calibrate the TOEM method.
3.2 Piezoelectric Microbalance
Pure materials such quart have a defined mechanical resonances, and the resonance frequency is a function of mass. Therefore, we can compare the resonance frequency with dust deposited on a crystal with a control crystal and determine the mass of deposited dust.
3.3 Beta Attenuation Monitor (BAM)
BAM technology accounted the loss of electrons as they penetrated through a filter. By comparing a blank filter (or the filter at time zero), we can determine the mass of dust that results in the loss of electrons from the source.
3.4 Pressure Drop Table Sampler
Dust deposited into a filter results in increment of headloss or a drop of pressure head.
3.5 Visible Light Scattering
By illuminating particles by a light source, light scattering in accordance to Mie Scattering effects. The mass of particles can be correlated by using a fitering method or by electromagnetic theory.
Nephelometers quantify particle light scatting over all directions.
3.7 Optical Particle Counter
Similar to Visible Light Scattering method, this method quantifies of particles in an air stream by counting number of particles and the sizes with an assumed mass density.
3.8 Condensation Nuclei Counter
This method is applied for untrafine particles by growing their sizes to the level can be detected by light scattering.
3.9 Aerodynamic Particle Sizer
This method measures both light scattering and time-of-flight of particles.
3.10 LIght Detection And Ranging (LIDAR)
LIDAR measures light scattering in the the direction of the light source. First, a pulsed laser sends to the atmosphere and the receiver, located closed to the emitter, the scattered light back by the suspended particles.
4. Shared features of desired methods
- Predictablity: a consistent and reliable relationship can be established.
- Comparability: the continuous monitoring can be traced back to the PM2.5 or PM10 standard method.
- Equivalence: this feature is a higher demanding than the two above. It requires the method demonstrate comparability and predictablity over a wide range of concentration and environment conditions.
5. Strong influence of high RH to light scattering method
6. What could cause PM change?
Diurnal variations: such as mixing close the ground level as the result of solar heatting/cooling.
Wind Speed: Wind speed is the indicator of the convective transportation.
Source Directionality: in combination with speed and direction.
7. Additional information
- An example of Standard Operating Precedure for Particulate Matter (PM) Gravimetric Analysis
- A guidance for sampling PM10 (Vietnamese) by VN CEM or backup PDF.