Assessment of the Contribution from Wood Burning to the PM10 Aerosol in Flanders, Belgium

Assessment of the contribution from wood burning to the PM10 aerosol in Flanders, Belgium

Willy Maenhaut1,2, Reinhilde Vermeylen2, Magda Claeys2, Jordy Vercauteren3, Christina Matheeussen3 and Edward Roekens3

1 Ghent University (UGent), Department of Analytical Chemistry, Krijgslaan 281, S12, 9000 Gent, Belgium 2 University of Antwerp (UA), Department of Pharmaceutical Sciences, Universiteitsplein 1, 2610 Antwerpen, Belgium 3 Flemish Environment Agency (VMM), Kronenburgstraat 45, 2000 Antwerpen, Belgium

Wood burning in PM10, Flanders 1 Introduction In Flanders (Belgium) we are struggling with too many exceedances of the 50 µg/m3 daily PM10 mass limit ¾ in the EU : only 35 exceedances per year allowed at any given location ¾ thus, of interest to examine the cause of possible exceedances Wood burning may provide a substantial contribution to the PM10 aerosol mass, as appeared from studies in several European countries (e.g., Switzerland, Austria) Over a decade ago, Simoneit et al., AE [1999] introduced levoglucosan as an indicator for wood burning

¾ levoglucosan (C6H10O5) arises from the pyrolysis of cellulose, the main building material of wood, at temperatures higher than 300 °C ¾ levoglucosan is accompanied by other minor stereoisomeric monosaccharide anhydrides in atmospheric aerosols, with mannosan and galactosan being the most important ones Flemish Environment Agengy (VMM) wanted to find out what the contribution from wood burning to PM10 was over a full year for 7 sites in Flanders ¾ thereby using levoglucosan as wood burning indicator

Wood burning in PM10, Flanders 2

Sampling

From 7 February 2010 to 6 February 2011 PM10 aerosol samples simultaneously taken every 4th day at 7 monitoring sites in Flanders, Belgium ¾ on 47-mm diam. Pallflex quartz fibre filters Two of the sites (i.e., Gent and Borgerhout) are urban background sites; Mechelen is a suburban background site, and the other 4 sites are rural background sites, whereby Hamme and Lier were expected to be particularly impacted by biomass burning

Wood burning in PM10, Flanders 3 Borgerhout : at 30 m from a busy road (Plantin en Moretuslei) Most polluted of the 2 urban background sites

Wood burning in PM10, Flanders 4 Gent : in the Baudelo park in the North-East of the city Least polluted of the 2 urban background sites

Wood burning in PM10, Flanders 5 Hamme : in a rural area with individual houses In the neigbourhood of the site are several inhabitants who use wood as fuel

Wood burning in PM10, Flanders 6 Houtem : rural background site In the middle of an agricultural area in the polders

Wood burning in PM10, Flanders 7 Meteorology

Precip. Temp. Wind dir.

40 360

35 315

30 270

25 225

20 180 mm, °C 15 135 Wind dir. (degrees) 10 90

5 45

0 0 09-Jul-10 21-Jul-10 01-Oct-10 13-Oct-10 25-Oct-10 04-Apr-10 16-Apr-10 28-Apr-10 05-Jan-11 17-Jan-11 29-Jan-11 03-Jun-10 15-Jun-10 27-Jun-10 10-Feb-11 03-Feb-10 15-Feb-10 27-Feb-10 11-Mar-10 23-Mar-10 02-Aug-10 14-Aug-10 26-Aug-10 07-Sep-10 19-Sep-10 06-Nov-10 18-Nov-10 30-Nov-10 12-Dec-10 24-Dec-10 10-May-10 22-May-10

Of the 92 sampling days: 60 days with rain

Wood burning in PM10, Flanders 8 Meteorology (cont.) 25

10 Number of days

19 10 2 7 21 18 7 8 0 NNE ENE ESE SSE SSW WSW WNW NNW (0-45) (45-90) (90-135) (135-180) (180-225) (225-270) (270-315) (315-360)

Wind direction mostly from South-West and North-North-East

Wood burning in PM10, Flanders 9 Analyses

PM10 mass determined by weighing of the filters at 20 °C and 50% relative humidity [done by VMM] Organic, elemental, and total carbon [OC, EC, and TC (= OC + EC)] measured with a dual photo-detector (2PD) thermal-optical instrument from Sunset Lab ¾ using NIOSH temperature protocol ¾ transmission (TOT) and reflectance (TOR) simultaneously measured ¾ TOT data retained for further evaluation Levoglucosan, mannosan, and galactosan measured by gas chromatography / mass spectrometry (GC/MS) after trimethylsilylation, using method described in Pashynska et al., J. Mass Spectrom. [2002], but ¾ extraction with methanol ¾ use made of a different recovery standard (RS) ¾ and slightly modified GC temperature program employed

Wood burning in PM10, Flanders 10 Schematic diagram of the Sunset Laboratory TOT instrument (V = valve)

Wood burning in PM10, Flanders 11 Thermogram for Gent PM10 sample of 13 July 2010 (transmission) 4000 He 1200 He:O2 3500 Laser T Temp. 1000 3000 FID Split 800 2500

2000 600

1500 400 Laser T (rel. units) Laser T (rel. 1000 Temp. (°C); FID (rel. units) 200 500 OC1 PC EC 0 0 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 Time (s)

OC = OC1 + PC (with PC: pyrolytic carbon) : area below the blue line prior to the OC/EC split point (vertical brown line) EC : area below the blue line after the OC/EC split point

Wood burning in PM10, Flanders 12 He Thermogram for Gent PM10 sample of 13 July 2010 He:O2 8000 Laser R 1200 Laser T 7000 Temp. 1000 FID 6000 Split R Split T 800 5000

4000 600

3000

Laser (rel. units) 400 2000 Temp. (°C); FID (rel. units) 200 1000

0 0 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 Time (s)

Full brown line : laser transmission (T) signal ¾ vertical full brown line : OC/EC split point for T Dashed purple line : laser reflectance (R) signal ¾ vertical dashed purple line : OC/EC split point for R

Wood burning in PM10, Flanders 13 Wood burning in PM10, Flanders 14 Total ion current (TIC) chromatogram [relative abundance (R.A.) versus time] obtained for the sample that was collected on 23 February 2010 in Hamme. The numbered peaks are for the following compounds: 1: galactosan: 60.6 ng/cm2; 2: mXP: 510 ng/cm2 (added); 3: mannosan: 145 ng/cm2; 4: levoglucosan: 826 ng/cm2.

Wood burning in PM10, Flanders 15 Comparison of TOT and TOR results TOR provided systematically larger EC data than TOT ¾ thus, TOR provided systematically lower OC data than TOT

6 Borgerhout, R801 Gent, R701 5 Mechelen, ML01 Hamme, HA02 Lier, LR02 4 Retie, RT01 Houtem, N029 TOT

/EC 3 TOR EC 2

0 09-Jul-10 21-Jul-10 04-Apr-10 16-Apr-10 28-Apr-10 01-Oct-10 13-Oct-10 25-Oct-10 03-Jun-10 15-Jun-10 27-Jun-10 05-Jan-11 17-Jan-11 29-Jan-11 03-Feb-10 15-Feb-10 27-Feb-10 11-Mar-10 23-Mar-10 10-Feb-11 06-Nov-10 18-Nov-10 30-Nov-10 02-Aug-10 14-Aug-10 26-Aug-10 07-Sep-10 19-Sep-10 12-Dec-10 24-Dec-10 10-May-10 22-May-10

Wood burning in PM10, Flanders 16 TOR/TOT ratio for EC as a function of season 3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 TOR/TOT ratio for EC for ratio TOR/TOT 0.6 0.4 0.2 1.4 1.4 1.3 1.4 1.5 1.5 1.6 1.3 1.4 1.8 1.6 1.7 1.5 1.4 1.7 2.0 2.0 2.0 2.0 2.6 1.7 1.8 1.6 1.7 2.1 1.9 2.0 1.9 1.9 2.2 1.5 1.5 1.4 1.5 1.5 0.0 Borgerhout Gent Mechelen Hamme Lier Retie Houtem

ALL Spring Summer Fall Winter

Some tendency for higher ratios at rural sites than at urban sites ¾ exception: Houtem Some tendency for higher ratios in winter than in the other seasons

Wood burning in PM10, Flanders 17 TOR/TOT ratio for OC versus TC loading on filter

7 y = 0.0002x2 + 0.0148x + 1.297 R2 = 0.2709 6 TOT

/EC 5 TOR 4 EC

0 0 102030405060708090 TC (µg/cm2)

Wood burning in PM10, Flanders 18 Time series for the PM10 mass at the 7 sites

110 Borgerhout, R801 100 Gent, R701 Mechelen, ML01 90 Hamme, HA02 80 Lier, LR02

) Retie, RT01 3 70 Houtem, N029 g/m µ 60

40 PM10 mass ( PM10

0 09-Jul-10 21-Jul-10 04-Apr-10 16-Apr-10 28-Apr-10 01-Oct-10 13-Oct-10 25-Oct-10 05-Jan-11 17-Jan-11 29-Jan-11 03-Jun-10 15-Jun-10 27-Jun-10 10-Feb-11 03-Feb-10 15-Feb-10 27-Feb-10 11-Mar-10 23-Mar-10 06-Nov-10 18-Nov-10 30-Nov-10 12-Dec-10 24-Dec-10 02-Aug-10 14-Aug-10 26-Aug-10 07-Sep-10 19-Sep-10 10-May-10 22-May-10

Fairly good correlation between the data of the 7 sites At Gent: 3 samples in a row in July with elevated levels ¾ these samples taken during the “Ghent City Festival”

Wood burning in PM10, Flanders 19

Retie (RT) Lier (LR) Mechelen (ML) Borgerhout (BO) Hamme (HA) Gent (GE) Houtem (HO)

Wood burning in PM10, Flanders 20 Correlation coefficients for the PM10 mass data of the 7 sites RT LR ML BO HA GE HO Retie 1 Lier 0.96 1 Mechelen 0.97 0.97 1 Borgerhout 0.95 0.96 0.97 1 Hamme 0.82 0.85 0.86 0.86 1 Gent 0.71 0.75 0.71 0.71 0.64 1 Houtem 0.74 0.75 0.74 0.70 0.61 0.65 1 3 "Ghent City Festival" samples excluded RT LR ML BO HA GE HO Retie 1 Lier 0.96 1 Mechelen 0.97 0.97 1 Borgerhout 0.95 0.96 0.97 1 Hamme 0.82 0.85 0.86 0.86 1 Gent 0.89 0.91 0.91 0.92 0.82 1 Houtem 0.74 0.75 0.74 0.70 0.61 0.75 1

Wood burning in PM10, Flanders 21 Time series for EC at the 7 sites

Borgerhout, R801 4.5 Gent, R701 Mechelen, ML01 4.0 Hamme, HA02 Lier, LR02 3.5 Retie, RT01 Houtem, N029 3.0 ) 3 2.5 g/m µ (

TOT 2.0 EC 1.5

1.0

0.5

0.0 09-Jul-10 21-Jul-10 04-Apr-10 16-Apr-10 28-Apr-10 01-Oct-10 13-Oct-10 25-Oct-10 05-Jan-11 17-Jan-11 29-Jan-11 03-Jun-10 15-Jun-10 27-Jun-10 10-Feb-11 03-Feb-10 15-Feb-10 27-Feb-10 11-Mar-10 23-Mar-10 06-Nov-10 18-Nov-10 30-Nov-10 02-Aug-10 14-Aug-10 26-Aug-10 07-Sep-10 19-Sep-10 12-Dec-10 24-Dec-10 10-May-10 22-May-10

EC levels highest at Borgerhout, lowest at Houtem Clearly less correlation between the data from the different sites than was the case for the PM10 mass

Wood burning in PM10, Flanders 22 Correlation coefficients for EC data of the 7 sites

RT LR ML BO HA GE HO Retie 1 Lier 0.84 1 Mechelen 0.75 0.85 1 Borgerhout 0.69 0.73 0.92 1 Hamme 0.82 0.89 0.76 0.66 1 Gent 0.52 0.63 0.66 0.56 0.62 1 Houtem 0.67 0.61 0.56 0.44 0.60 0.47 1

Wood burning in PM10, Flanders 23 Median EC/TC ratios

0.40

0.35

0.30

0.25

0.20

/TC ratio for PM10 0.15 TOT

EC 0.10

0.05

0.32 0.24 0.20 0.13 0.18 0.15 0.17 0.00 BO GE ML HA LR RT HO

Wood burning in PM10, Flanders 24 Time series for OC at the 7 sites

18 Borgerhout, R801 Gent, R701_o 16 Gent, R701 Mechelen, ML01 14 Hamme, HA02 Lier, LR02 12 )

3 Retie, RT01 Houtem, N029

g/m 10 µ (

TOT 8 OC 6

Fairly good correlation between the data of the 7 sites At Gent: 3 samples in a row in July with elevated levels ¾ these samples taken during the “Ghent City Festival”

Wood burning in PM10, Flanders 25 Correlation coefficients for OC data of the 7 sites

RT LR ML BO HA GE HO Retie 1 Lier 0.96 1 Mechelen 0.94 0.94 1 Borgerhout 0.96 0.96 0.96 1 Hamme 0.64 0.68 0.75 0.72 1 Gent 0.85 0.88 0.86 0.87 0.63 1 Houtem 0.80 0.82 0.82 0.84 0.55 0.74 1

3 "Ghent City Festival" samples excluded Retie 1 Lier 0.96 1 Mechelen 0.94 0.94 1 Borgerhout 0.96 0.96 0.96 1 Hamme 0.64 0.68 0.75 0.72 1 Gent 0.92 0.94 0.95 0.96 0.72 1 Houtem 0.80 0.82 0.82 0.84 0.55 0.82 1

Wood burning in PM10, Flanders 26 Gent sample of 13 July 2010

Wood burning in PM10, Flanders 27 Gent sample of 21 July 2010

Wood burning in PM10, Flanders 28 Gent sample of 29 July 2010

Wood burning in PM10, Flanders 29 Time series for OC at the 7 sites

18 Borgerhout, R801 Gent, R701_o 16 Gent, R701 Mechelen, ML01 14 Hamme, HA02 Lier, LR02 12 )

3 Retie, RT01 Houtem, N029

g/m 10 µ (

TOT 8 OC 6

Fairly good correlation between the data of the 7 sites At Gent: 3 samples in a row in July with elevated levels ¾ these samples taken during the “Ghent City Festival”

Wood burning in PM10, Flanders 30 Median TC/PM10_mass ratios

0.25

0.20

0.15

0.10 TC/PM ratio for PM10

0.05

0.18 0.16 0.18 0.18 0.16 0.15 0.10 0.00 BO GE ML HA LR RT HO

Wood burning in PM10, Flanders 31 Time series for levoglucosan at the 7 sites

1.6 1.5 Borgerhout, R801 1.4 Gent, R701 1.3 Mechelen, ML01 1.2 Hamme, HA02 ) 3 1.1 Lier, LR02

g/m 1.0 Retie, RT01 µ 0.9 Houtem, N029 0.8 0.7 0.6

Levoglucosan ( 0.5 0.4 0.3 0.2 0.1 0.0 09-Jul-10 21-Jul-10 04-Apr-10 16-Apr-10 28-Apr-10 01-Oct-10 13-Oct-10 25-Oct-10 03-Jun-10 15-Jun-10 27-Jun-10 05-Jan-11 17-Jan-11 29-Jan-11 11-Mar-10 23-Mar-10 03-Feb-10 15-Feb-10 27-Feb-10 10-Feb-11 06-Nov-10 18-Nov-10 30-Nov-10 02-Aug-10 14-Aug-10 26-Aug-10 07-Sep-10 19-Sep-10 12-Dec-10 24-Dec-10 10-May-10 22-May-10

High levels in winter & fall; low levels in spring & summer Time series for Hamme quite peculiar

Wood burning in PM10, Flanders 32 Correlation coefficients for levoglucosan data of the 7 sites RT LR ML BO HA GE HO Retie 1 Lier 0.96 1 Mechelen 0.92 0.96 1 Borgerhout 0.96 0.95 0.96 1 Hamme 0.61 0.62 0.62 0.65 1 Gent 0.86 0.90 0.93 0.94 0.67 1 Houtem 0.76 0.81 0.82 0.82 0.47 0.85 1

The levoglucosan data for 5 of the 7 sites (i.e., Retie, Lier, Mechelen, Borgerhout, and Gent) are very highly correlated with each other (all r>0.9, except 0.86 between Retie and Gent) ¾ indicating that the impact from wood burning at these 5 sites was a regional phenomenon

Wood burning in PM10, Flanders 33 1.2 y = 1.14x 2 R = 0.91 Mechelen Lier 1 y = 1.12x Gent R2 = 0.91 Retie )

3 Linear (Mechelen) 0.8 y = 1.01x

g/m Linear (Lier)

µ 2 R = 0.87 Linear (Gent) Linear (Retie) y = 0.92x 0.6 R2 = 0.91 Levoglucosan ( 0.4

0.2

0 0 0.2 0.4 0.6 0.8 1 Borgerhout - Levoglucosan (µg/m3)

Wood burning in PM10, Flanders 34 1.6 y = 1.88x Hamme 2 1.4 R = 0.32 Houtem Linear (Hamme) Linear (Houtem) 1.2 ) 3 g/m

µ 1

0.8

Levoglucosan ( 0.6 y = 0.62x R2 = 0.67 0.4

0.2

0 0 0.2 0.4 0.6 0.8 1 Borgerhout - Levoglucosan (µg/m3)

Wood burning in PM10, Flanders 35 Data for mannosan and galactosan

A each site : mannosan and galactosan very highly correlated with each other and with levoglucosan ¾ all r > 0.95 (except at Hamme : 0.93 between levoglucosan and mannosan) Levoglucosan/mannosan (L/M) ratio depends on the type of biomass and wood burnt ¾ Miocene lignite 54 Fabbri et al., AE [2009] ¾ Peat 8.6 Kourtchev et al., STE [2011] ¾ Bituminous coal 3.1 Kourtchev et al., STE [2011] ¾ US woods, fireplaces Fine et al., EES [2004] − hardwoods 13-24 − softwoods 3.9-6.7 ¾ Austrian wood stoves Schmidl et al., AE [2008] − hardwoods 14-15 − softwoods 3.6-3.9

Wood burning in PM10, Flanders 36 Data for mannosan and galactosan

The annual average L/M ratios for our 7 sampling sites ranged from 6.2 to 7.1 and there was little variation with season ¾ suggests that softwood burning was clearly more important than hardwood burning in Flanders in 2010-2011 Schmidl et al., AE [2008] provided the following equation for estimating the %spruce burned from the L/M ratio : %spruce = (14.8 – L/M_ratio) / 0.112 ¾ this equation used to estimate the %spruce burned at our 7 sites

Wood burning in PM10, Flanders 37 %spruce as a function of season 100

%spruce 40

10 73 77 70 73 70 70 77 66 69 66 73 77 80 69 70 78 82 76 78 75 72 74 72 69 70 76 77 79 72 72 72 70 87 66 68 0 Borgerhout Gent Mechelen Hamme Lier Retie Houtem

ALL Spring Summer Fall Winter

Typically between 70 and 80% from spruce burning ¾ little variation from site to site ¾ little variation with season

Wood burning in PM10, Flanders 38 Contribution from wood burning to the OC and the PM10 mass

To assess the percentage contribution from wood burning to the OC, we relied on the concentrations of 9.3% levoglucosan and 52% OC in wood smoke as given by Schmidl et al., AE [2008] ¾ meaning that the levoglucosan level is multiplied by a factor of 5.59 (i.e., 52/9.3) to obtain the OC concentration from wood smoke Similarly, we used the conversion factor of 10.7, suggested by Schmidl et al., AE [2008], to convert our levoglucosan concentrations to PM10 mass levels due to wood smoke

Wood burning in PM10, Flanders 39 Time series for %OC from wood burning at the 7 sites

120 Borgerhout, R801 110 Gent, R701 Mechelen, ML01 100 Hamme, HA02 90 Lier, LR02 80 Retie, RT01 Houtem, N029 70

% of OC due to wood burning% of OC due to wood 30

0 09-Jul-10 21-Jul-10 04-Apr-10 16-Apr-10 28-Apr-10 01-Oct-10 13-Oct-10 25-Oct-10 05-Jan-11 17-Jan-11 29-Jan-11 03-Jun-10 15-Jun-10 27-Jun-10 11-Mar-10 23-Mar-10 10-Feb-11 03-Feb-10 15-Feb-10 27-Feb-10 06-Nov-10 18-Nov-10 30-Nov-10 02-Aug-10 14-Aug-10 26-Aug-10 07-Sep-10 19-Sep-10 12-Dec-10 24-Dec-10 10-May-10 22-May-10

High values in winter & fall; low levels in spring & summer Time series for Hamme quite peculiar

Wood burning in PM10, Flanders 40 %OC from wood burning as a function of season 70

30 mean ± s.d. 20

20 15 3 26 36 21 14 3 28 40 23 18 3 27 43 36 25 14 46 60 25 20 4 32 43 23 19 4 28 43 22 15 2 30 40 0 Borgerhout Gent Mechelen Hamme Lier Retie Houtem ALL Spring Summer Fall Winter

In winter (blue) for 6 of the 7 sites : around 40% of OC, on average, from wood burning At Hamme in winter : 60% of OC, on average, from wood burning

Wood burning in PM10, Flanders 41 Annual medians of the % OC due to wood burning at the 7 sites

%OC from wood burning 10

5 18 18 18 33 24 23 17 0 BO GE ML HA LR RT HO

Wood burning in PM10, Flanders 42 Time series for %PM from wood burning at the 7 sites

70 65 Borgerhout, R801 60 Gent, R701 Mechelen, ML01 55 Hamme, HA02 50 Lier, LR02 45 Retie, RT01 40 Houtem, N029 35 30 25 20 % of PM due to wood burning % of PM 15 10 5 0 09-Jul-10 21-Jul-10 04-Apr-10 16-Apr-10 28-Apr-10 01-Oct-10 13-Oct-10 25-Oct-10 03-Jun-10 15-Jun-10 27-Jun-10 05-Jan-11 17-Jan-11 29-Jan-11 11-Mar-10 23-Mar-10 03-Feb-10 15-Feb-10 27-Feb-10 10-Feb-11 06-Nov-10 18-Nov-10 30-Nov-10 02-Aug-10 14-Aug-10 26-Aug-10 07-Sep-10 19-Sep-10 12-Dec-10 24-Dec-10 10-May-10 22-May-10

High values in winter & fall; low levels in spring & summer Time series for Hamme quite peculiar

Wood burning in PM10, Flanders 43 %PM10 from wood burning as a function of season 25

10 mean ± s.d.

5 2.8 0.7 7 9 5 2.7 0.7 8 9 6 3.8 0.9 9 11 13 7.3 5.0 19 22 6 3.5 1.0 10 11 6 3.4 1.1 9 10 5 1.9 0.5 7 9 0 Borgerhout Gent Mechelen Hamme Lier Retie Houtem ALL Spring Summer Fall Winter

In winter (blue) for 6 of the 7 sites : around 10% of PM10 mass, on average, from wood burning At Hamme in winter : 22% of PM10 mass, on average, from wood burning

Wood burning in PM10, Flanders 44 Annual medians of the % PM due to wood burning at the 7 sites

3 %PM from wood burning 2

1 3.2 3.4 4.5 8.6 3.9 4.3 2.4 0 BO GE ML HA LR RT HO

Wood burning in PM10, Flanders 45 Annual medians of the % EC in PM10 at the 7 sites

/PM10 perc. ratio perc. /PM10 4

TOT 3 EC 2

1 5.1 3.3 3.2 2.2 2.6 2.2 1.7 0 BO GE ML HA LR RT HO

Wood burning in PM10, Flanders 46 Summary and conclusions

Wood burning is an important contributor to the OC and PM10 mass in Flanders, especially in winter ¾ 40 % of OC in winter typically from wood burning (60% at Hamme) ¾ 8% of PM10 mass in winter typically from wood burning (18% at Hamme) Since most of the exceedances of the 50 µg/m3 daily PM10 mass limit occur in winter, reducing the wood burning emissions would help in complying with the EU limit of maximum 35 exceedances per year at any given location Wood burning smoke is a regional phenomenon in Flanders ¾ in Hamme: nearby sources very important This study published in Sci. Total Environ. ¾ Maenhaut et al., STE 437 (2012) 226-236

Wood burning in PM10, Flanders 47 Wood burning in PM10, Flanders 48 Wood burning in PM10, Flanders 49 Mechelen : at about 1 km from the inner ring of the city Suburban background site

Wood burning in PM10, Flanders 50 Lier : rural site; within a radius of 1 km were two horticulture farms that used wood as fuel, but it appeared in the course of the project that one of the two farms had already stopped its activities at the start of the project

Wood burning in PM10, Flanders 51 Retie : rural background site In a meadow, next to a wooded park (Prinsenpark)

Wood burning in PM10, Flanders 52 Gent sample of 17 July 2010

Wood burning in PM10, Flanders 53 Gent sample of 25 July 2010

Wood burning in PM10, Flanders 54 Gent sample of 2 August 2010

Wood burning in PM10, Flanders 55