POLYCHLORINATED DIBENZODIOXINS AND DIBENZOFURANS EMISSIONS FROM TRANSPORTATION

Persistent Organic Pollutants (POPs) represent group of organic compounds with specific physico-chemical and environmental-chemical properties. The most important among them are resistance to diverse degradation processes, low solubility in water, lipophilic character. These properties results in high tendency for bioaccumulation, semi volatility enabling global atmospheric transport and significant adverse effects on human health or environment. Polychlorinated Dibenzodioxins (PCDDs) and Polychlorinated Dibenzofurans (PCDFs) belong among others to this group of compounds. They originate during communal, hospital or dangerous wastes incineration, also during coal, peat and wood combustion and can be also determined in vehicles emissions [1]. Their content in exhaust gasses is in very small concentrations and because of difficult and complicated analytical determination these compounds are measured in exhaust gasses only sporadically [2].


Introduction
Persistent Organic Pollutants (POPs) represent group of organic compounds with specific physico-chemical and environmental-chemical properties. The most important among them are resistance to diverse degradation processes, low solubility in water, lipophilic character. These properties results in high tendency for bioaccumulation, semi volatility enabling global atmospheric transport and significant adverse effects on human health or environment. Polychlorinated Dibenzodioxins (PCDDs) and Polychlorinated Dibenzofurans (PCDFs) belong among others to this group of compounds. They originate during communal, hospital or dangerous wastes incineration, also during coal, peat and wood combustion and can be also determined in vehicles emissions [1]. Their content in exhaust gasses is in very small concentrations and because of difficult and complicated analytical determination these compounds are measured in exhaust gasses only sporadically [2].

Measurements methodology
Emission factors (Ef) measurements of three vehicles using four different types of fuel were performed in two sampling campaigns in 2009 and 2010. Standard city cycle in accordance with ECE 83.04B consisting of 4 cycles ECE 15 in 195 sec. (Fig. 1) in three repetitions with previous 5 minutes engine heating up to running temperature (SDC) was chosen to simulate urban driving. Sufficient amount of exhaust gasses for PCDD/Fs and Polyaromatic Hydrocarbons (PAH) determination was sampled during these three cycles. Sampling was performed by using apparatus described in Fig. 2 connected directly to exhaust pipe. All measurements were performed in authorized station for vehicles homolo-gation TUV SUD on dynamometer SCHENCK 364/GS56 that simulates flywheel mass and running resistance as if vehicle moves on the road. PCDD/Fs isotopic marked congeners were placed before the sampling to the sorption system to ensure control of PCDD/Fs sorption efficiency. Sampling and analyses were performed in accordance with CSN EN 1948-1-3 considering that measurements next to exhaust pipe was not possible to perform isokinetically. The same apparatus was used also for PAH sampling. Basic emission parameters such as CO 2 , CO, HC, NO 2 were also measured at the same time.
Vehicle thus passed through the test in accordance with speed profile that is standard and described in ECE 83 regulation. Exhaust gasses were sampled in the whole volume using HORIBA CVS 7300 T device and were diluted to prevent condensation. Fuels used for measurements were tanked in common petrol stations. Their average chemical composition is characterised by parameters shown in Tab. 3. Symbols n H and n C mean the amount of hydrogen and carbon atoms in the mean molecule of fuel, ρ p means fuel density, BA is 95 octane gasoline and MN summer diesel fuel.

Ef calculation methodology
Methodology results from Ef values of CO, NO x , CO 2 and HC measured in dry exhaust gasses on dynamometer by standard methods and from fuel consumption. Ef of pollutants are calculated from measured concentration and measured volumes of dry exhaust gasses used for chosen pollutants sampling under normal conditions (101.325 kPa, 0 °C).
Symbols marked with upper index on the right side are related to dry gasses that means to gasses without any water vapours. Amount of substances entering the combustion process are marked with capital N with appropriate indexes, amount of substances of It is necessary to know fuel composition when calculating Ef. The meanings of factors used for calculations are described in Table 1, physical constants in Table 2. Stoichiometric coefficients are introduced for simplification of further equations and their meaning is evident from equation (4) . ( If atomic ratio H:C (ϭ β) and oxygen percentage content π O are known, then . ( From the equation for fuel molecular weight relative to one carbon atom after substitution from (1) and (2), it holds (3) Emission factors of limited pollutants calculation results from equations of fuel combustion, mass balance and measured values. Fuel combustion is considered in some simplification (it is assumed that hydrocarbons contained in exhaust gasses are identical to those contained in fuel, origin of trace concentrations of PAH, N 2 O, NH 3 and others are not considered): Mass balance of real fuel combustion considering presumptions characterised above can be described by following equations for separate elements: and equation solution for unknown parameters N s V a N p brings formula necessary for further calculations n n n n n n N n If pollutant concentration is expressed in mass units per volume unit, Ef of separate components of exhaust gasses relative to unit of consumed fuel can be described as . (13) Ef expressed in mass units per passed route and concentration input data in mass unit per volume unit of exhaust gasses are calculated as . ( Then results from equation (14) for rates for conversion from separate pollutants concentrations in exhaust gasses (POPs in this case) to Ef after substitution of the molar fraction from equation (11) and after neglecting NO 2 concentration (NO predominantly originates during combustion): The result from equation (14) is used for Ef calculation relative to passed route. After substitution of the result from equation (15) in dimensions described in Table 2

Results and discussion
Emission factors of common pollutants that were also used for POPs Ef calculations are described in Table 3. Upper index p means unburned hydrocarbons Congener profiles for j-th measurement (17) or cumulative congener profiles (18) were compiled on the basis of measured data in accordance with following equations where index i represents appropriate PCDD or PCDF congener. Cumulative Efs are counted above all PCDD and PCDF congeners. Following PCDD congeners and their toxic equivalents were considered: Table 3 Legend: t means tanked in petrol station (same in   Significant differences were found out among cumulative TEQ Ef in particular years. Predominant influence of Ef measured in 2010 was demonstrated by comparison of arithmetic and geometric averages. Usage of sum of sequences of Ef measured in appropriate campaign and year according to their value is not dependent on absolute values of measured cumulative Ef (Fig. 5). In accordance with this criterion, PCDD/F Ef of Felicia with gasoline fuel had the highest toxic equivalent while PCDD/F Ef of the same vehicle using LPG fuel had the lowest toxic equivalent. Emission factors TEQ for conventional fuels (gasoline, diesel) decreased with decreasing age of vehicle. Usage of LPG in the same vehicle significantly decreased POPs emission in comparison with usage of conventional fuel. LPG had the lowest PCDD/F Ef among studied fuels.

Results of limited pollutants emission factors measurements
Determined POPs Efs were compared with Efs measured by CDV for a wider selection of vehicles during 2005 -2006 [3,4]. Summary of measuring conditions in 2005 -2010 is outlined in Table 4. Most of fuels were certificated. Trend of dependency of cumulative PCDD/F Ef sums for separate vehicles and fuel on measuring date for separate measuring campaign (one day or two days) is shown in Fig. 6. Efs of cold starts (CS) are also shown in this graph. Cold start represents SDC without pre heating after vehicle parking outside whole night and its movement onto the dynamometer with engine off.
Efs had similar character of their time progress. This time progress was in four campaigns similar to time progress of PAH Efs. Data variance was larger within the sampling campaigns than among campaigns. Geometric averages of Efs measured in campaigns were in the range of units up to tens of pg.km Ϫ1 (in the frame in Fig. 6). However, PCDD/F Efs were in two campaigns in 2006 lower (tenths to units of pg.km Ϫ1 ) and in the last campaign in 2010, on the contrary, hundreds to thousands of pg.km Ϫ1 .
Since differences in PAH Efs measurements in contrast to PCDD/F Efs were not relevant, entrance of different amounts of chlorine or its compounds to the measuring systems in these three campaigns than in others was considered. Probably these compounds were contained in the air entering combustion process in vehicles engines.
Cold starts Efs were higher than Efs measured under running conditions for all fuels which is probably determined by different  Cumulative TEQ emission factors for all the measuring campaigns, all the tested vehicles and fuels shown in Fig. 7

Acknowledgement
This study was supported by the Czech Ministry of Transport within R&D project "POPs emissions from transport" No. CG912-081-520.