Particles size and composition in Mediterranean countries:
geographical variability and short-term health effects
MED-PARTICLES Project 2011-2013
Under the Grant Agreement EU LIFE+ ENV/IT/327
Particles size and composition in Mediterranean countries:
geographical variability and short-term health effects
MED-PARTICLES
ACTION 12.
Effect modification of Saharan dust advection days and of forest fires days on the
association between particles and health endpoints: city-specific results and metaanalysis
Report on: Effect modification of Saharan advection days
Summary: Report on the methods and the results of the identification of Saharan dust advection days
and the investigation of the effect modification in the Mediterranean cities involved in the MEDPARTICLES project.
----------------------------------------------------
Introduction
Atmospheric pollution is depending on two main factors: emissions and meteorology. Temporal
variations of emissions and meteorological parameters are controlling the concentrations and trends
of atmospheric pollutants, both gaseous and particles. The aim of this part of the project is to
ascertain on the origin of air masses reaching receptor points, specifically Saharan dust outbreak
These episodes are common in the Mediterranean region and usually increase PM levels at a
regional scale.
To date, evidence of the impact of Saharan dust events on health is still limited. Conflicting results
have been reported in studies on the effects of Saharan advection events on mortality and few
studies have reported health effects of Saharan dust on daily morbidity in Europe.
In the paper by Pey et al. 2012, member of the MED-PARTICLES study group, the first results
about the methodology applied in the project for the identification and quantification of desert dust
events in the Mediterranean basin have been presented. It has been shown a decreasing gradient of
African dust outbreaks frequency South to North of the Mediterranean basin during the period
2001-2010, with the lowest average frequencies observed in Central and NE Spain, SE France and
Northern Italy, while the highest frequency is recorded in Sicily.
The average contribution of African dust to the mean ambient air PM10 levels has been estimated
and is considerably higher in the eastern locations of the Mediterranean when compared to those
observed in the western side. Average annual concentrations were found to be maximum in Cyprus
and Greek Islands, and minimum in NE Spain, SE France and North Italy.
It has been demonstrated that the mean annual African dust contributions in PM 10 varied with
respect to the latitude and a longitudinal effect is patent from 25ºE eastwards. In addition, it has
been observed that the decreasing gradient of African dust towards the North is not linear but
exponential.
We aimed to evaluate the associations between different particle fractions and health outcomes, and
the effect modification of dust advection episodes on these associations in the cities involved in the
project.
Methods
Exposure assessment
Data from 19 regional background and sub-urban background sites were obtained in order to
evaluate African dust contributions across the Mediterranean Basin and to assess their impact on
PM10 levels. African dust episodes have been identified by using a methodology consisting in the
interpretation of different web available tools: meteorological products (NCEP/NCAR), aerosol
maps (BSC-DREAM; NAAPS-NRL; SKIRON), satellite images (Sea-WiFS; MODIS) and air
masses back-trajectories (HYSPLIT).
In order to quantify the daily African dust contributions to PM10 and PM2.5 concentrations, the 30
days moving 40th percentile of the PM data series have been calculated, after excluding those days
impacted by African dust, and subtracted from the experimental PM concentration for the day under
evaluation.
Health data
We studied natural, cardiovascular and respiratory mortality, and cardiovascular and respiratory
hospitalizations as the main health outcomes of this analysis.
Daily counts of these outcomes have been collected for 13 cities in Italy, Spain, Greece and France,
from 2001 to 2011.
Analysis
A Saharan dust event has been defined mild if a dust advection is occurring and the PM desert
contribution at the ground level is present but below 10 µg/m3, intense if a dust advection is
occurring and the desert contribution to PM is above 10 µg/m3.
Percentage increased risk (%IR) of natural, cardiovascular and respiratory mortality, and of
cardiovascular and respiratory hospitalizations for residents (all ages for mortality and age 15+ for
hospital admissions) were obtained for each city from Poisson regression models, using a casecrossover approach. The short-term effects of a 10µg/m3 increase of PM10 were estimated at
different latencies, according to previous analyses of the main effects, and adjusted for time trend,
temperature and barometric pressure. We first inspected the effects of PM10 by season and then by
the presence of dust, adding an interaction term between the PM exposure term and the binary
indicator for the dust, to test the presence of an effect modification on the PM-mortality or PMhospitalizations association.
Furthermore we estimated the effects of both components of PM, testing the possible non linearity
of the desert component.
Pooled estimates were obtained from a random-meta-analysis, for 11cities for which we have the
Saharan dust estimation. We calculated then the p-value of the relative effect modification (p-REM)
for the pooled results and the I2 statistic of Higgins.
Results
We analysed data of desert dust advection and African contribution to PM in eleven cities of the
MED-PARTICLS project. The study period varies among cities depending on the availability of
data from the meteorological tools and from the regional background monitoring sites. The city
with the higher number of days with intense episodes of desert dust is Palermo (15.1%), followed
by Athens (14.4%) (Table 1). The distribution of mild and intense episodes is homogeneous for
almost all the cities, except for Madrid, where the intense episodes are twice the number of the mild
ones.
Most of the intense dust episodes occur during winter in Milan, Marseille, Barcelona and Athens,
and during spring in all the other cities, except in Madrid, where most of the intense dust days
happen during summer.(Figure 1)
Table 1. Descriptive statistics of desert dust events
CITY
Milan
Turin
Emilia-Romagna
Bologna
Marseille
Rome
Barcelona
Thessaloniki
Madrid
Athens
Palermo
Study
period
2007-2010
2006-2010
2008-2010
2006-2010
2006-2008
2005-2010
2003-2010
2007-2009
2001-2009
2007-2009
2006-2009
No desert
dust days
Mild
episodes of
desert dust
N
%
Intense
episodes of
desert dust
N
%
Total days
N
%
N
%
1,277
87.4
69
4.7
102
7.0
1,461 100.0
1,612
88.3
99
5.4
100
5.5
1,826 100.0
988
90.1
67
6.1
29
2.6
1,096 100.0
1,578
86.4
129
7.1
74
4.1
1,826 100.0
882
80.5
101
9.2
94
8.6
1,096 100.0
1,809
82.6
209
9.5
151
6.9
2,191 100.0
2,518
86.2
195
6.7
170
5.8
2,922 100.0
898
81.9
65
5.9
45
4.1
1,096 100.0
2,714
82.6
158
4.8
288
8.8
3,287 100.0
775
70.7
124
11.3
158
14.4
1,096 100.0
976
66.8
197
13.5
220
15.1
1,461 100.0
50.0
Intense episodes
Mild episodes
Cold season
% days
40.0
30.0
20.0
10.0
0.0
50.0
Intense episodes
Mild episodes
Spring
% days
40.0
30.0
20.0
10.0
0.0
50.0
Intense episodes
Mild episodes
Summer
% days
40.0
30.0
20.0
10.0
0.0
Figure 1: Seasonal distribution of mild and intense episodes of desert dust
During the cold season (Table 2), the desert component of PM10 increases during intense desert dust
days compared (Intense DDD) with no desert dust days (No DDD) for all the cities. This happens
also for the anthropogenic component for Emilia-Romagna, Bologna, Madrid and Palermo. For
seven cities out of eleven the concentration of the anthropogenic component is higher during intense
episodes than during mild, but this doesn’t happen for Milan, Marseille, Rome and Madrid, where
the anthropogenic component decreases.
In Milan, Emilia-Romagna, Marseille, Madrid and Thessaloniki there is a higher increase of PM2.5
than of PM2.5-10 during intense DDD. On the contrary, in Rome and Athens the coarse fraction
increases more than the fine fraction during intense days.
During spring the desert component increases, while the anthropogenic decreases, but not in
Athens. The PM2.5 fraction has a lower increase in concentration from mild to intense DDD, but it is
the opposite for Barcelona and Thessaloniki.
In summer the desert and the anthropogenic PM10 components reduce when the intensity of desert
dust events increases, but not in Milan, Marseille and Athens. PM2.5 has a lower increase in
concentration from mild to intense DDD. In Barcelona, Thessaloniki , Madrid and Athens it
happens that the coarse fraction increases more than the fine fraction when considering more
intense DDD.
In Table 3 there are the results of the analysis on cause-specific mortality, at the pre-defined
latency.The effects of PM10 in the whole year is 0.51% (95%CI:0.27;0.75) on natural mortality,
0.66% (95%CI:-0.02;1.34) on cardiovascular mortality, and 2.01% (95%CI:0.92;3.12) on
respiratory mortality. The effects are higher during spring (1.53%%, 2.15%,4.42% for natural,
cardiovascular and respiratory mortality, respectively) and during the desert dust days with desert
PM10 concentration above 0 µg/m3 (0.48% vs 0.74%,p-REM=0.372 for natural mortality; 0.59% vs
1.06%, p-REM=0.596 for cardiovascular mortality; 2.04% vs 2.64%, p-REM=0.684 for respiratory
mortality), nevertheless there is no evidence of an effect modification.
The effects of the desert and the anthropogenic PM10 are higher for respiratory mortality (1.28%,
95%CI:-0.42;3.01 and 2.43%, 95%CI:0.94;3.95, respectively).
On the risk on natural and cardiovascular mortality it seems to be more important the exposure to
PM10 from desert than the exposure to anthropogenic PM10. This is not true for the respiratory
mortality, where the anthropogenic PM10 has a higher effect than the desert PM10 (2.43% and
1.28%, respectively). The risk of natural and cardiovascular mortality increases when the desert
PM10 concentration goes above 20 µg/m3.
The effects of the desert and anthropogenic PM10 components are higher and statistically significant
during spring for natural and respiratory mortality . For cardiovascular mortality the highest effect
of desert PM10 occurs during spring (2.30%;95%CI:0.00;4.65) and that of anthropogenic PM10
during summer (2.48%;95%CI:0.21;4.79).
The city-specific and pooled effects of desert and anthropogenic PM10 are plotted in the forest plots
in Figure 2.
The effects of PM10 on the hospital admissions are positive and statistically significant for
cardiovascular diseases (0.29%, 95%CI:0.00;0.58), respiratory diseases (0.69%, 95%CI:0.20;1.19),
and respiratory admission of people aged 0-14 years (1.66%, 95%CI:0.93;2.39) (Table 4).
The effect of PM10 is higher during spring for cardiovascular admissions (1.34%) and during
summer for respiratory admissions of adult people and of children (2.95% and 14.77%,
respectively).There is an increase in the risk of cardiovascular and respiratory admissions of people
aged 15+ when considering the presence of desert dust events , on the other hand the risk is higher
during no dust days for respiratory hospitalizations of children. The exposure to the desert
component of PM10 has a higher risk on respiratory admission of children, more than that of the
anthropogenic component (2.38% vs 1.76%).
The effects of the desert and anthropogenic PM10 components are higher during spring for
cardiovascular admissions and during summer for respiratory admissions of children. There is no
clear evidence of an effect modification of the presence of desert dust on the association between
PM10 and hospitalizations.
Table 2: Mean concentrations of PM10 components, PM2.5 and PM2.5-10 during mild and intense desert dust days (DDD) by season
Desert PM10
Anthrop. PM10
PM2.5
PM2.5-10
COLD
SEASON
Milan
Turin
Emilia-R.
Bologna
Marseille
Rome
Barcelona
Thessaloniki
Madrid
Athens
Palermo
No
DDD
Mild
DD
Intense
DD
No
DDD
Mild
DD
Intense
DD
No
DDD
Mild
DD
Intense
DD
No
DDD
Mild
DD
Intense
DD
0
5
34
61
51
38
45
32
51
16
12
19
0
5
38
68
47
50
51
39
68
-
-
-
0
5
18
44
42
60
30
28
47
14
18
31
0
5
17
48
49
57
34
37
49
-
-
-
0
5
23
25
22
12
18
13
24
6
7
8
0
5
19
38
32
31
23
21
25
12
14
22
0
5
25
35
45
34
24
34
43
11
16
16
0
6
21
52
54
49
30
35
43
20
24
27
0
6
30
34
42
40
17
20
30
17
19
38
0
6
34
32
31
32
19
21
28
13
15
37
0
5
32
31
31
35
-
-
-
-
-
-
Desert PM10
SPRING
Milan
Turin
Emilia-R.
Bologna
Marseille
Rome
Barcelona
Thessaloniki
Madrid
Athens
Palermo
Anthrop. PM10
Milan
Turin
Emilia-R.
Bologna
Marseille
Rome
Barcelona
Thessaloniki
Madrid
Athens
Palermo
PM2.5-10
Mild
DD
Intense
DD
No
DDD
Mild
DD
Intense
DD
No
DDD
Mild
DD
Intense
DD
No
DDD
Mild
DD
Intense
DD
0
5
18
28
26
20
17
17
20
12
15
19
0
5
20
26
25
25
16
18
25
-
-
-
0
4
17
23
25
23
13
16
21
9
13
19
0
4
22
27
26
21
17
20
26
-
-
-
0
5
18
23
24
24
13
16
20
9
8
19
0
5
18
28
28
28
15
17
21
11
15
24
0
5
20
36
39
39
22
26
36
14
19
23
0
5
19
42
37
33
27
27
33
16
15
19
0
6
24
27
33
30
12
19
24
12
18
24
0
5
33
33
33
38
21
25
35
12
14
36
0
5
25
30
31
29
-
-
-
-
-
-
Desert PM10
SUMMER
PM2.5
No
DDD
Anthrop. PM10
PM2.5
PM2.5-10
No
DDD
Mild
DD
Intense
DD
No
DDD
Mild
DD
Intense
DD
No
DDD
Mild
DD
Intense
DD
No
DDD
Mild
DD
Intense
DD
0
6
18
26
22
25
14
16
24
13
9
17
0
6
19
26
18
16
17
18
27
-
-
-
0
5
27
24
23
18
13
14
20
11
13
24
0
5
22
26
25
19
15
19
20
-
-
-
0
6
19
23
20
21
12
15
23
10
10
19
0
6
21
30
28
24
16
18
22
13
14
22
0
5
18
31
32
26
19
22
30
12
15
14
0
5
25
41
40
36
26
30
39
14
15
22
0
6
25
33
35
28
17
21
29
16
20
28
0
7
23
32
35
38
24
29
40
9
13
21
0
5
23
29
30
25
-
-
-
-
-
-
Table 3: Percent increases in risk of natural, cardiovascular and respiratory mortality, associated to exposure to PM 10 and its component and correspondent 95% confidence interval.
Natural mortality 0+,
lag 0-1
Mortality
%
95%CI p-REM
Cardiovascular mortality 0+,
lag 0-5
I2
p-het
%
95%CI p-REM
Respiratory mortality 0+,
lag 0-5
I2
p-het
%
95%CI p-REM
I2
p-het
PM10
0.51
0.27;0.75
-
22
0.233
0.66
-0.02;1.34
-
40
0.084
2.01
0.92;3.12
-
31
0.148
PM10 , cold season
0.34
0.12;0.55
-
0
0.668
0.41
-0.15;0.97
-
15
0.304
1.64
0.59;2.70
-
16
0.289
PM10 , spring
1.53
0.93;2.13
-
0
0.613
2.15
0.80;3.52
-
0
0.447
4.42
1.93;6.98
-
0
0.939
PM10 , summer
1.29
0.57:2.02
-
1
0.429
2.07
0.57;3.59
-
0
0.776
2.90
-1.48;7.49
-
31
0.153
PM10 , No DDD
0.48
0.18;0.78
-
26
0.197
0.59
-0.04;1.23
-
24
0.215
2.04
0.62;3.49
-
46
0.048
PM10 , desert PM10 > 0 mg/m3
0.74
0.25;1.23
0.372
17
0.278
1.06
-0.54;2.68
0.596
54
0.016
2.64
1.02;4.27
0.592
0
0.684
.
.
Desert PM10
0.66
0.27;1.06
-
0
0.748
1.10
0.15;2.05
-
0
0.766
1.28
-0.42;3.01
-
0
1.000
Anthropogenic PM10
0.53
0.23;0.83
0.600
32
0.147
0.47
-0.39;1.33
0.336
46
0.045
2.43
0.94;3.95
0.323
41
0.073
-
-
-
-
-
-
-
-
-
-
-
Desert PM10 1-10
0.76
-0.72;2.26
-
45
0.050
0.02
-1.25;1.31
-
0
0.448
0.67
-2.57;4.01
-
26
0.200
Desert PM10 11-20
-0.09
-2.48;2.36
-
45
0.052
1.16
-1.57;3.96
-
0
0.472
-0.03
-4.82;4.99
-
0
0.965
Desert PM10 > 20
2.57
0.71;4.46
-
0
0.579
2.09
-1.17;5.47
-
28
0.177
0.38
-0.25;1.02
-
0
0.875
Cold season: desert PM10
0.74
0.17;1.32
-
6
0.387
0.82
-0.42;2.09
-
0
0.509
0.50
-1.71;2.75
-
0
0.945
Cold season: anthropogenic PM10
0.28
0.02;0.54
0.150
5
0.397
0.20
-0.53;0.95
0.404
26
0.200
2.29
0.68;3.92
0.205
40
0.083
Spring: desert PM10
1.15
0.30;2.00
-
0
0.493
2.30
0.00;4.65
-
10
0.349
4.12
0.52;7.84
-
0
0.951
Spring: anthropogenic PM10
1.90
1.09;2.72
0.210
0
0.748
2.34
0.21;4.53
0.977
0
0.846
4.97
1.16;8.92
0.755
0
0.941
Summer: desert PM10
0.17
-1.18;1.54
-
15
0.304
0.80
-1.76;3.43
-
0
0.876
0.52
-4.13;5.39
-
0
0.544
Summer: anthropogenic PM10
1.41
0.59;2.23
0.129
0
0.639
2.48
0.21;4.79
0.344
7
0.373
3.66
-2.94;10.70
0.457
43
0.064
Effect modification of Desert dust days (DDD)
Two PM components
Desert PM10 = 0
Figure 2: Forest plot of the effects of desert and anthropogenic PM10 on natural mortality (lag 0-1)
Table 4: Percent increases in risk of cardiovascular and respiratory hospital admissions associated to exposure to PM 10 and its component and correspondent 95% confidence interval.
Cardiovascular admissions 15+,
lag 0-1
Hospital admissions
%
95%CI p-REM
Respiratory admissions 15+,
lag 0-5
I2
p-het
%
95%CI p-REM
Respiratory admissions 0-14,
lag 0-5
I2
p-het
%
95%CI p-REM
I2
p-het
PM10
0.29
0.00;0.58
-
41
0.105
0.69
0.20;1.19
-
32
0.175
1.66
0.93;2.39
-
0
0.475
PM10 , cold season
0.14
-0.10;0.38
-
0
0.465
0.43
-0.10;0.97
-
23
0.246
1.18
0.21;2.15
-
19
0.276
PM10 , spring
1.34
0.66;2.04
-
3
0.409
1.76
0.64;2.90
-
0
0.596
3.07
0.42;5.78
-
0
0.445
PM10 , summer
1.27
0.61;1.93
-
0
0.581
2.95
1.71;4.21
-
0
0.704
14.77
6.07;24.17
-
65
0.005
PM10 , No DDD
0.30
-0.11;0.72
-
63
0.009
0.64
-0.03;1.31
-
52
0.041
1.78
0.65;2.92
-
28
0.205
PM10 , desert PM10 > 0 mg/m3
0.51
0.04;0.99
0.510
0
0.508
1.10
0.29;1.92
0.390
0
0.942
0.97
-0.67;2.63
0.427
0
0.450
Desert PM10
0.23
-0.30;0.76
-
0
0.503
0.67
-0.48;1.83
-
10
0.352
2.38
0.09;4.71
-
9
0.363
Anthropogenic PM10
0.36
-0.02;0.75
0.688
59
0.016
0.67
0.14;1.19
0.994
21
0.266
1.76
0.60;2.94
0.641
24
0.235
Effect modification of Desert dust days (DDD)
Two PM components
Desert PM10 = 0
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Desert PM10 1-10
0.29
-0.76;1.35
-
0
0.832
0.04
-1.13;1.23
-
0
0.666
0.52
-1.97;3.06
-
2
0.413
Desert PM10 11-20
0.73
-1.35;2.86
-
24
0.236
0.47
-2.10;3.11
-
0
0.824
-0.90
-6.17;4.66
-
0
0.567
Desert PM10 > 20
-0.06
-2.25;2.19
-
0
0.841
1.28
-3.12;5.89
-
43
0.092
6.53
-2.78;16.72
-
53
0.039
Cold season: desert PM10
-0.10
-0.94;0.75
-
18
0.285
0.58
-0.83;2.01
-
0
0.643
1.94
-1.87;5.91
-
42
0.096
Cold season: anthropogenic PM10
0.20
-0.13;0.53
0.521
30
0.190
0.35
-0.40;1.10
0.776
43
0.091
1.40
-0.51;3.34
0.805
54
0.035
Spring: desert PM10
1.10
-0.16;2.38
-
11
0.346
1.65
-0.59;3.95
-
9
0.360
2.57
-4.16;9.77
-
32
0.176
Spring: anthropogenic PM10
1.42
0.64;2.21
0.670
0
0.538
1.64
0.16;3.14
0.991
0
0.904
5.17
-0.41;11.07
0.572
37
0.136
Summer: desert PM10
1.07
-0.01;2.16
-
0
0.813
1.53
-0.74;3.87
-
0
0.710
3.00
-7.06;14.15
-
30
0.189
Summer: anthropogenic PM10
1.13
0.40;1.87
0.924
0
0.750
3.84
2.23;5.48
0.110
0
0.789
19.11
10.02;28.94
0.028
50
0.052
Conclusions:

We found a clear short-term effect of PM10 on natural and respiratory mortality during desert dust
days

We also found a significant effect of PM10 on cardiovascular and respiratory admissions of people
aged 15+ during desert dust days.

The desert and anthropogenic PM10 components have higher effects on respiratory mortality and
respiratory admissions of children.

The effect of the desert PM10 component increases during spring and summer.