Chemistry Reference
In-Depth Information
3.2 General Characterization of LRT Smoke Particles
The most often measured property of the LRT wildfire smokes is the mass concen-
tration of aerosol particles in fine (PM
2.5
) or submicron (PM
1
) or in fine and coarse
size fraction together (PM
10
). The mass concentration is usually determined either
with a tapered element oscillating microbalance (e.g., [
19
]), or with the instruments
based on
-attenuation (e.g., [
13
]). In addition to mass concentration, real-time
instruments can measure other physical properties of particles, e.g., number con-
centration of particles in different size fractions using a differential mobility
particle sizer [
13
] or the optical characteristics of smoke by a nephelometer [
32
].
Ground-based instruments also include remote sensing instruments such as sun
photometers [
32
].
Organic carbon (OC) and elemental carbon (EC) concentrations in smoke
aerosol can be measured by using a semicontinuous thermal-optical OC/EC
instruments [
18
]. Water-soluble organic carbon (WSOC) and water-soluble ions
can be detected in smoke plumes with a PILS combined with a total organic carbon
analyzer [
30
] and IC [
19
]. Besides smoke-specific tracers, the HR-ToF-AMS
enables to study the concentrations of organic matter (OM), nitrate, ammonium,
sulfate, and chloride in smoke particles [
30
]. Black carbon (BC) can be measured in
real-time with several instruments, e.g., with aethalometer [
19
], multi-angle absorp-
tion photometer [
29
], and particle soot absorption photometer [
25
].
As already mentioned, smoke particles can also be studied by collecting them on
a filter and analyzing that in the laboratory. However, collected smoke particles can
transform during the sampling or sample preparation [
12
]. The advantage of the
filter methods is that smoke samples are available for several different chemical
analytical techniques. In addition to OC, EC, WSOC, and ions, also the elemental
composition of smoke aerosol can be determined from the filter samples [
22
].
Typically chemical components are analyzed from the bulk samples, but the
elemental composition can also be determined for individual smoke particles by
scanning electron microscope coupled with an energy-dispersive X-ray
microanalyzer [
12
]. With filter samples the composition of organic fraction in
aerosol can be explored in detail. From biomass burning samples, e.g., dicarboxylic
acids [
14
] and polycyclic aromatic hydrocarbons (PAHs;
b
[
23
]) have been
determined.
Most widely used space born measurement for the wildfire studies is MODIS.
There are two MODIS's onboard satellites and they cover the Earth's surface every
1-2 days. MODIS gives information on the location of fires and also on the optical
properties of aerosol. Optical properties of the smoke particles have also been
studied by using the ozone monitoring instrument [
32
] onboard EOS-Aura satellite.
Cloud-aerosol lidar with orthogonal polarization provided the vertical profile of the
plume during the smoke episode in 2010 [
32
]. In addition to comparison with
ground-based instruments, the data from the space born instruments has been used
in the modeling of smoke plumes (e.g., [
10
]).
