Airborne particulate matter is today recognized as an important category of air
pollutants. Current air quality standards, and hence most particle instruments,
are based on particle mass concentration-the European standard, for example,
on the PM10 fraction. For other metrics, such as number concentration, there is
currently a lack of suitable instrumentation for monitoring purposes. A novel realtime
particle-counting instrument has been developed in an attempt to fill this gap.
The new instrument is capable of detecting and counting particles from about
10 nm to 10 pm particle diameter. This instrument, aimed at monitoring ambient air
quality, uses a parallel combination of optical particle counting for larger particles
plus condensation particle counting for the smallest particles. The particles are
classified into several size fractions, which allows discrimination between ultrafine,
fine, and coarse particles. The instrument also enables gravimetric measurement of
PM10 or PM2.5 providing the possibility of comparing the measured number concentrations
with the mass concentration standards. Furthermore, a conversion of
the number concentration data into PMIO.P. M2.5,a nd also PMl mass concentration
is possible. The new instrument is unique in offering number and mass information
over the complete size range of interest in urban air quality monitoring.
The design of the instrument and the development and construction of first prototypes
are described as well as calibration and performance results. The performance
tests included side-by-side comparisons of two identical prototypes and
comparison studies with traditional instrumentation in an urban field environment
at a monitoring station in Birmingham (UK). Here, very good correlation was observed
between the ultrafine particle concentration indicated by the new instrument
and the total number concentration measured by a CPC (TSI model 3022A).
Number-to-mass conversion results correlated well with mass concentration measured
by TEOM.
Possibilities for a further size fractionation in the ultrafine particle size range
were investigated and selected techniques tested. Size separation using diffusion
devices was identified as a suitable technique to be implemented in the new instrument
for ultrafine fractionation. Other future possibilities for further developments
are also discussed