AEROSOL SCIENCE & TECHNOLOGY
INTRODUCTION
Aerosols,
which are particles suspended in the air, significantly affect our daily
life. From the early history, aerosols have been playing a critical role
in the evolution of the planet (e.g. rain, snow, dust wind). In the
modern societies, many anthropogenic pollutants are in the form of aerosols or
are associated with aerosols (such heavy metal emissions, dioxin, acid rain,
ozone depletion by CFC). Meanwhile, scientists are developing materials
of next-generation using aerosol technology (e.g. nanosized particles
possessing completely different properties from their bulk materials, drug
delivery). Understanding the aerosol mechanism involved in these
processes, hence, are very important. Following are some examples.
CONDENSATION CHARACTERISTIC TIME
Condensation
is a gas-to-particle conversion process and is an important mechanism for
particle growth. It is the major reason of particle growth for
atmospheric aerosols. It can also be used to coat materials.
In an aerosol
system, there are several mechanisms competing simultaneously. Although
numerical models can be used to precisely simulate the various mechanisms and
determine the importance of individual mechanism in the system, a simple
expression of characteristic time can offer a convenient and first-hand
estimation. Condensation characteristic times have been developed
assuming either constant vapor concentration or constant particle size.
However, systems with simultaneous vapor depleting and particle size increase
are often encountered. Thus, a new condensation characteristic time
considering both are important, which is the objective of this research work.
Related
publication
1.
Wu, C. Y. and Biswas, P., "Particle
Growth by Condensation in a System with Limited Vapor", Aerosol Science
and Technology, 28(1), 1-20, 1998.
AEROSOLS IN PHOSPHATE INDUSTRY
Workers in their workplace are constantly exposed to aerosols. These aerosols containing chemicals may enter
the body through the respiratory route and deposit in the lung. The physical and chemical properties of the
aerosol ultimately determine the fate in and health effects on human beings.
Currently
we are conducting a project for the Florida Institute of Phosphate Research to
evaluate the health risks in the phosphate industry due to inhalation of
aerosols. The concern results from
TENORM (Technologically Enhanced Naturally Occurring Radioactive Materials)
that is due to the processing of phosphate ore containing natural
radioactivity. A UW cascade impactor is
used to collect aerosols by their aerodynamic size. The size-fractionated aerosol is then
measured by g-ray spectroscopy for its radioactivity. The activity size distribution is then used
in a lung deposition and clearance model (an ICRP-66 based LUDEP model) to
calculate their effective dose for assessing the health risks. It is also planned to determine the
solubility of the aerosol that can critically affect its fate in the body.
Preliminary
results show that radioactive materials in aerosol are different from their
products and settled dust in the facility, implying different sources of these
radioactive materials. In addition, fine
aerosols tend to have a high radioactivity level than the coarse aerosols
do. The final results will help
determine how to further protect the health of workers in the facilities.
Figure 1 UW
cascade impactor (housing and various stages)
Table
1A Activity size distribution of
sampled aerosol
|
Air sampling |
|
|||||
|
Stage |
Mass |
Activity Concentration (pCi/g) |
||||
|
|
(mg) |
U-238 |
Ra-226 |
Pb-210 |
K-40 |
|
|
1 |
1187 |
MDC |
34.9 |
267.0 |
1324.7 |
|
|
2 |
340 |
MDC |
112.9 |
1160.3 |
5417.6 |
|
|
3 |
753 |
MDC |
86.8 |
MDC* |
MDC |
|
|
4 |
203 |
MDC |
406.2 |
MDC |
1066.7 |
|
|
5 |
157 |
MDC |
584.0 |
MDC |
5986.0 |
|
|
6 |
87 |
MDC |
990.0 |
793.8 |
7824.2 |
|
|
7 |
147 |
MDC |
675.0 |
778.6 |
1913.2 |
|
|
F |
457 |
MDC |
237.4 |
408.8 |
2036.7 |
|
|
* : MDC : Less than Minimum Detectable Concentration |
||||||
Table
1B Radioactivity of settled dust and
products
|
Settled Dust and Products |
|
||||
|
Samples |
Activity Concentration (pCi/g) |
||||
|
|
U-238 |
Ra-226 |
Pb-210 |
K-40 |
|
|
Settled Dust |
31.30 |
0.29 |
6.90 |
0.18 |
|
|
MAP |
0.90 |
0.57 |
6.10 |
0.29 |
|
|
DAP |
1.30 |
0.26 |
6.38 |
MDC |
|