Since 1970, the General Physics Department of «Università degli Studi di Torino» has carried out a project research, on inorganic solid particulate matter. The special issue of Annals of Geophysics, published for Professor Giorgio Fioccos 70th birthday, gives us the possibility to make some important remarks on this topic, focusing on PM2.5. This has been possible using all the old and new experimental data of the measures made by the authors of this paper since 1970

Casazza, M.

Piano, A.

Earth-prints Repository

241
ANNALS OF GEOPHYSICS, VOL. 46, N. 2, April 2003
Some remarks on PM2.5
Marco Casazza and Angelo Piano
Dipartimento di Fisica Generale «A. Avogadro», Università di Torino, Italy
Abstract
Since 1970, the General Physics Department of «Università degli Studi di Torino» has carried out a project 
research, on inorganic solid particulate matter. The special issue of Annals of Geophysics, published for Professor 
Giorgio Fiocco’s 70th birthday, gives us the possibility to make some important remarks on this topic, focusing on 
PM2.5. This has been possible using all the old and new experimental data of the measures made by the authors 
of this paper since 1970.
Mailing address: Dr. Angelo Piano, Dipartimento di 
Fisica Generale «Avogadro», Università di Torino, Via P. 
Giuria 1, Torino, Italy; e-mail: piano@to.infn.it
Key  words  PM2.5 – solid inorganic particulate 
matter
1.  Introduction
Since 1970, the General Physics Department 
of «Università degli Studi di Torino» has car-
ried out a research project on inorganic solid 
Particulate Matter (PM) (Longhetto et al., 1975; 
Bacci et al., 1983). The purpose was to obtain 
not only knowledge about the mass concentration 
of PM2.5, but also to understand the correlations 
with climatological and meteorological factors. 
Recently, we devoted more attention to indoor 
measurements and on outdoor-indoor infl uences. 
The special issue of Annals of Geophysics,
published for Professor Giorgio Fiocco’s 70th 
birthday, gives us the possibility to make some 
important remarks on this topic. This has been 
possible collecting the experimental data of 
measures (old and new ones) made by the authors 
of this over during more than 30 years.
The particles, dispersed in the atmosphere, 
with an aerodynamic diameter of less than 2.5 mm
(PM2.5) have been studied with great accuracy 
because, being considered the respirable fraction 
of Suspended Particulate Matter (SPM), they can 
reach the inner parts of the respiratory apparatus 
and hence the alveoli. 
2.  Dimensional spectra and associated             
     chemical elements
Around 1970 we started to measure the 
concentrations of inorganic particles, for the 
purpose of characterising the emissions of 
sources of great intensity and the immission in 
the environment in the neighbourhood of the 
studied sources. At that time, the granulometric 
distribution of the dimensions of particles, 
expressed as DN/D (logr) (% of total), was in 
good agreement with the theoretical one of Noll 
and Pilat (1971), for dust of continental origin. 
We saw, analysing more than 2  106 samples
collected both in urban and rural sites, using 
the technique of Atomic Absorption Spectro-
photometry (AAS), that the chemical elements 
associated to the Suspended Particulate Matter
(SPM), like Pb, Cd, V, are associated with parti-
cles of smaller diameter (fi g. 1), while Al, Cu, Fe 
are not so much linked to PM2.5 (fi g. 2). 
After 25 years, the granulometric distribution 
has changed and, today, particularly in the urban 
environment, a typical representation of its trend 
can be shown using fi g. 3.
242
Marco Casazza and Angelo Piano
This distribution of mass concentration was 
obtained using an Andersen 2000 Inc. (1977) 
non-viable cascade impactor (Andersen, 1958; 
Vaughan, 1989), which is composed of 8 different 
stages and permits the collection of PM with 
aerodynamic diameter of less than 11 mm.
The fraction with aerodynamic diameter of 
less than 0.8 mm is much increased respect to the 
particles of larger dimensions. This is confi rmed 
by the growth by two orders of magnitude, of 
the concentration of number per unit volume, 
of Aitken nuclei (diameters from 0.01 mm to 
0.1 mm), that, nowadays, in urban environment, 
reach some units multiplied by 105 per unit vol-
ume (cm3).
3.  Correlation with meteorological factors
We considered it useful to have continuous 
measures of mass concentration. Those were 
made using a DustTrak 8520 aerosol monitor, 
produced by TSI (2001). Many temporal se-
quences, during the last 6 years, and the know-
ledge of the contemporary measures of the val-
ues of the meteorological parameters, such as so-
lar radiation, wind speed and direction, relative 
humidity, temperature and quantity of rain, give 
us the possibility to understand the infl uence of 
many phenomena on the mass concentration 
trend. The meteorological measures were carried 
out in several sites of Northern Italy and, in 
particular, in the Turin CNR area, where RASS, 
SODAR and other devices are present to measure 
vertical profi les of wind, relative humidity and 
temperature.
We can see, as an example, in fi g. 4, a frag-
ment of a temporal sequence collected during 
March 2001.
Fig.  1.  Means of 256 measures of Pb, Cd and V 
granulometric distributions in several different places 
in the Po Valley. 
Fig.  2.  Means of 384 measures of Al, Cu and Fe 
granulometric distributions carried out in Northern 
Italy.
Fig.  3. Current and old (25 years ago) granulometric 
distributions of inorganic particulate matter with aero-
dynamic diameter from 0.43 mm to 11 mm compared
with Noll and Pilat’s (1971) theoretical continental 
granulometric aerosol distribution.
243
Some remarks on PM2.5
The data used for this graph are automatically 
collected, with different programmable sampling 
times, by the instrument and analysed by its 
software, that furnishes a graphic representation 
of the mass concentration trend, like the one 
shown above, with an error of 2 mg m-3. We 
showed this measure of 6 days because it starts 
and fi nishes with a rainfall and because it is 
visible how, in urban areas during winter, an 
accumulation phenomenon is present that can 
lead to aerosol concentrations higher than 
0.5 mg m-3. This is evident from Friday 9th and 
Tuesday 13th (note that the increasing trend is 
present on Sunday too, when it can be referred 
only to road traffi c or to domestic heating). The 
spikes that are present during the different days 
are linked with diurnal, meteorological or local 
factors.
Using some other fi gures, we will give an inter-
pretation to some recurrent phenomena, mak-
ing a qualitative comparison between PM2.5 and 
some meteorological variables.
Figure 5 shows the PM2.5 concentration trend 
compared with the variations of wind speed. In 
this case wind is responsible, moving air masses, 
of the visible spikes and of the dilution of the 
PM2.5 concentration in the examined area.
Figure 6 shows a period characterized by 
the presence of a rainfall. PM2.5, considering 
its dimensions, is not reduced directly and im-
mediately by rain itself but, more easily, by its 
associated wind. A deeper analysis of this phe-
nomenon becomes necessary considering that, in 
every rainfall event, a variable period of stable 
concentration is present, visible under the form of 
a more or less pronounced bend in the graph.
Figure 7 helps us to explain this particular 
concentration trend. After the beginning of the 
rainfall, after a fall in PM2.5 mass concentra-
tion, both relative humidity and PM2.5 show an 
Fig.  4.  Temporal sequence in urban area obtained using DustTrak 8520 in  March 2001. 
A
er
os
ol
 (
m
g
/m
-3
)
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
March 2001
Thu 8 Fri 9 Sat 10 Sun 11 Mon 12 Tue 13 Wed 14
244
Marco Casazza and Angelo Piano
Fig.  5.  Qualitative comparison between wind speed 
and PM2.5 mass concentration.
Fig.  6.  Qualitative comparison between rain trend 
and PM2.5 concentration.
Fig.  7.  Qualitative comparison between relative 
humidity and PM2.5 trends.
increase, while, after that, a further decrease of 
the two parameters considered is visible. This 
might be explained considering that the aerosol 
might be composed of condensation nuclei too, 
that can actively participate in the precipitation 
thereby making a contribution to the reduction 
of relative humidity.
Figure 8 shows the frequently found, in the 
case of very fi ne weather conditions, correlation 
between the PM2.5 concentration trend and the 
variation of the solar radiation during a day of 
measures.
Using different (more than 2.5  106 measures 
of 1 min each) of this kind and the related me-
teorological data, we can affi rm that:
–  PM2.5 are not immediately removed by 
rainfalls.
–  They are taken away by wind or taken 
around the point of measure from areas with 
different rate of pollution.
–  They have a diurnal modulation, linked 
with traffi c and industrial production.
–   They refl ect particular local emissions.
–    In conditions of dynamic equilibrium, they 
characterise the area in which the measures take 
place and the activities done in that particular 
place.
–  They are a witness more of the path 
followed by different air masses than their 
peculiar characteristics.
245
Some remarks on PM2.5
Fig.  8.  Trends of PM2.5 and solar radiation.
4.  Indoor measures
The last two characteristics found experi-
mentally are of great interest for indoor measures, 
considering, in particular, environments without 
particular sources and without smokers, like an 
offi ce. 
If particular sources are present, like the 
smoke of one cigarette, as shown in fi g. 9, it is 
possible to see a rapid and marked increase in 
PM2.5 concentration; the time needed to return to 
the original values of concentration can be some 
days. The measure presented here was taken in 
an offi ce of about 70 m3 in conditions of thermal 
equilibrium.
In terms of Aitken nuclei, we can say that the 
inspired and expired smoke contains, in number 
concentration, on average, 7  105 particles cm-3.
The other characteristics, deduced observing 
the results of many (more than 103) indoor mea-
Fig.  9.  PM2.5 mass concentration induced by cigarette smoke in 70 m3 room in thermal equilibrium.
246
Marco Casazza and Angelo Piano
sures (domestic too), can be summarised saying 
that:
–   Household appliances intaking air (vacuum 
cleaners and so on ...) do not retain, through the 
fi lter, PM2.5.
–  Common domestic activities lift or gene-
rate PM2.5 (mainly during cleaning or cooking 
or frying).
–   The exchange with outdoor air depends on 
pre existing concentrations (indoor and outdoor) 
and on differences of temperature.
-  Often, the operation of changing the air of 
an indoor environment has the effect of inducing 
a worse air quality.
5.  Conclusions
Using the data of our measures, we can affi rm 
that PM2.5 concentrations are greatly increasing. 
We are studying the chemical proprieties of this 
fraction of SPM, including its mutagenesis to 
defi ne its danger. PM2.5 concentrations are more 
poisonous indoors than outdoors, especially if 
there are some intense local sources, among 
which we can consider a smoker or some com-
mon household appliances. 
A better knowledge on PM2.5 can lead to 
important interventions, useful to reduce the risks 
for human health.
REFERENCES
ANDERSEN, A.A. (1958): A new sampler for the collection, 
sizing and enumeration of viable particles, J. Bacteriol.,
76, 471-484.
ANDERSEN 2000 INC. (1977): Operating manual for Andersen 
2000 Inc. 1 ACFM ambient particle sizing samplers 
(Andersen 2000 Inc., Atlanta, Georgia).
BACCI, P., A. LONGHETTO, G. MARCAZZAN, A. PIANO, F. 
PRODI, C. SABBIONI and A. VENTURA (1983): Aerosol 
characterization in a Po Valley site, in Proceedings of the 
Gesellschaft für Aerosolforschung meeting, J. Aerosol 
Sci., 14 (3), 222-225. 
LONGHETTO, A., P. PAVESE and A. PIANO (1975): Comparison 
among granulometric distributions of Pb and Cd on urban, 
bottom valley, and mountain atmospheric aerosols, in 
Proceedings of the 13th International Meeting on Alpine 
Meteorology, Riv. Ital. Geofi s., 1, 95-96.
NOLL, K.E. and M.J. PILAT (1971): Size distribution of 
atmospheric giant particles, Atmos. Environ., 5, 527-
540.
TSI (2001): Aerosol Monitor DustTrak 8520 Operating 
Instruction.
VAUGHAN, N.P. (1989): The Andersen impactor: calibration, 
wall losses and numerical simulation, J. Aerosol Sci.,
20, 67-90. 


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Some remarks on PM2.5

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