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Revision af beregninger af danske VOC emissioner fra opløsningsmidler og husholdninger

Summary

The latest inventory on non-methane volatile organic compounds (named VOC even though NMVOC is more correct) from December 2006 showed that the emissions from Denmark in 2010 will be around 89,000 tons. This is 4,000 tons more than the emission limit of 85,000 tons, in the EU NEC Directive on national emission ceilings, and the Gothenburg Protocol to the Geneva Convention on Long-range cross-border air pollution.

The projected emission of approx. 89,000 tons of VOC’s in 2010 is divided in the groups:

1. 28,000 tons from the use of solvents
2. 20,600 tons from households (stoves & garden tools / household)
3. 19,400 tons from the transport sector
4. 9,400 tons of storage and distribution of fuels
5. 11,600 tons by: Electricity and heat production, manufacturing, industrial processes stationary and mobile sources in the agriculture / forestry / fishing sector.

This project is a review of items 1 and 2 of the present inventory of the Danish VOC emission in order to assess the need for adjustments and recalculations.

Item 1 covers all use of VOC’s, both in the industrial, public and domestic sector.

Item 2 are VOC’s from households which primarily are VOC’s from combustion of wood in stoves and boilers.

Use of solvents

The procedure for the evaluation of the inventory on the use of solvent is:

• From the DMU 2006 inventory the 32 largest selected. These 32 substances or substance groups represented more than 98% of the total VOC emissions from the use of solvents.
• Vapour pressure and boiling point of each of the 32 VOC’s found by a literature search. This was done to determine whether the substances are covered by the definition in the guidelines for reporting of emission inventories /1/.
• Of the 32 VOC the 15 with the largest emissions selected for a detailed survey. The underlying data for the consumption of these substances were discussed in detail with the DMU.
• From this research the basis of data for some 10 substances was controlled by examining the sources (including SPIN2000 database that is used as a "key" to determine the total consumption in each sector and branch), contact to the Statistics Denmark, the Ministry for Taxation, and a number of Danish companies with a known and significant consumption of these VOC’s.

The study showed that four VOC’s fell outside the definition limit for vapour pressure, where only substances with vapour pressures greater than 0.01 kPa shall be included. The four VOC’s are glycerol, toluene diisocyanate, dioctylphthalate and diethylene glycol, and they are recommended to be completely removed from the survey.

Aminooxygengruppen covers 81 drugs, and there are randomly searched for boiling point and vapour pressure for 26 of these substances. Only date for 3 of the substances was found, and the vapour pressure was below 0.01 kPa for all of them. Since all the substances have relatively high molecular weight, and some are salts, it is unlikely that any of the substances in the aminooxygengroup should be classified as VOC’s, and they are therefore recommended to be completely removed from the survey.

For several other substances, especially methanol, naphthalene, propane, butane, ethylene glycol and formaldehyde, evidence has been found to recommend the use of lower emissions in the survey. This is based on inconsistencies between the actual consumption in industry and statements from Statistics Denmark and the consumption and distribution of industries in SPIN 2000.

By investigation of the consumption of ethanol and propylalcohol for the production of wind screen washing fluid, it was found that apparently it is entirely produced from imported ethanol, which is imported under the category of Anti-freeze preparations. This category has so far not been included in the VOC survey, and it recommended being included in the next version. The volume of 4,500 tonnes a year is an estimated figure informed by an importer, and better data can be gathered from DK Statistics.

Tabel 0-1 shows a summary of the VOC emissions survey and recommendations for change and thereby revised emission for the use of solvents.

Table 0-1. recommended changes in the VOC emission survey for the use of solvents

Overall, there are recommendations for reduction in the VOC emission survey of 12,168 tonnes a year, but since there has been found an unregistered consumption of ethanol under the category of Anti-freeze preparations washer fluid of around 4,500 t/y, the resulting recommended reduction is 7,668 tonnes a year. This corresponds to app. 23 % of the total emission from the use of solvents.

VOC’s from households

VOC emissions from households, which include stoves etc. and fuels for garden and other household tools is estimated to be 20,600 tonnes for the year 2006. The 17,109 tonnes is form heating and the remaining 3,500 tonnes are mainly fuels for lawnmowers and the like.

Out of the VOC emission from heating at 17,109 tonnes a year, wood and straw-fired furnaces and boilers accounts for 98 %, and wood-fired furnaces and boilers are predominant, with a VOC emission of 15,027 tonnes a year.

This part of the review is therefore concentrated to wood stoves and wood boilers.

The emission factors and firewood consumption used in the VOC survey is evaluated and especially examined if the used emission factors can be considered representative of Danish conditions, and potential better values are proposed.

The VOC survey for firewood are based on the annual wood consumption from the Energy Agency and the number and distribution on different types of stoves and boilers, for which emission factors are based on the EMEP/CORINAIR Emission Inventory Guidebook /6/, as shown in the table below.

Table 0-2. VOC emission calculations for wood stoves and wood boilers

*w.Bf means a buffer vessel is installed.

There are substantial uncertainties associated with this survey, because no exact knowledge of any of the input data exists. Several assumptions that have a large impact on the calculated emissions have been made, and these assumptions could just as well have been done differently.

The Danish National Environmental Researc Institute (NERI) uses the same high emission factor for the groups Old Stove and Newer Stove, where Technological Institute clearly state, that emission from Newer Stove is considerably lower than from Old Stove, and that the efficiency is much higher. This is based on the fact, that stoves in the category New Stove have been tested according to DS-887

Some measurements in two studies have been found covering Newer Stove, showing much lower emissions of NMVOC than the used emission factor of 1.200 g/GJ from CORINAIR. Mean values for NMVOC emissions in the two studies are respectively 240 g/GJ and 60 g/GJ, and on this basis they should be classified as Advanced Stoves in the CORINAIR classification, with has an emission factor of 250 g/GJ. Thereby, the total emission of wood combustion in the 2006 survey would be reduced by approx. 6,146 tons, from 15,027 to 8,881 tonnes, which would be an almost 50 % reduction.

The latest figures for firewood consumption in the Energy Statistics for 2007 show an increase of the consumption of firewood of almost 30%. This will increase the VOC emission to a level of about 21,000 tonnes a year, which is almost 25 % of allowed 85,000 tonnes a year according to the NEC directive. This increase in firewood consumption of almost 30% seems to be unrealistically high. We recommend evaluating the inventory method, which is based on telephone interviews, and especially trying to replace the estimation of the number of stoves and boilers, by information on exact numbers, e.g. collected from all the Danish Chimney sweepers.

VOC emissions from wood firing in contributing with a large part of the Danish emission ceiling, and there is great uncertainty on the emission factors. We therefore recommend that EPA implement a project designed to bring together existing measurements of VOC’s from Danish furnaces and boilers, and complements these values with measurements on a relevant range of furnaces and boilers, especially in categories Old Stoves and Newer Stoves. On such a background, more realistic emission factors for VOC emissions from combustion of wood can be fixed. Such an investigation is likely to cause a significant reduction in the estimated VOC emissions, compared to the current levels.

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Version 1.0 September 2009, © Miljøstyrelsen.