7.3 Measurement strategy with respect to defined measurement objectives
7.3.5 Identification of air pollutant sources
Examples of identification of air pollution sources by a large field study involving diffusive samplers and questionnaires are given in [38,50,51]. To identify air pollutant sources the elements of sampling strategy shall be used as follows in addition to the basic information as given in [52] and 7.2.2 to 7.2.7:
— Time of sampling
Simultaneous sampling is required to rule out the dependency of pollutant concentrations with all time related conditions. The sampling time is less important.
— Sampling duration and sampling frequency
The duration of sampling is less important provided the limits of determination for all compounds of interest are exceeded. Sampling frequency depends on the degree of success and the resource available.
— Sampling site and determinations with resolution in space
To identify the source it is advisable to divide the room into different areas and to simultaneously sample at a site in each area. However, such a procedure will only be successful if the individual areas of the room can be classified as similar in terms of ventilation, which is not always the case, particularly in artificially ventilated rooms.
Furthermore, diffusive samplers can be sited as near as possible to suspected sources, e.g. on book shelves, at the outlet of ventilation systems, near the vent of electronic devices and floor or wall coverings, in cabinets. Substantially elevated concentrations at these sites relative to the concentration simultaneously gained at a representative site in the room will identify a source. But it shall be kept in mind that due to a spatial influence of the object under investigation on the uptake rate of the diffusive sampler (excessive or reduced air movement, see 5.4.4.1 and 5.4.4.2) the quantification of the measurements may be influenced.
More detailed study would involve an investigation of the emission characteristics of material suspected to be a relevant pollutant source using respective guidelines [53]. These will provide traceable and reproducible results of emission characteristics of material and products.
— Simultaneous ambient air measurements
If there are indications of substantial pollutant sources outside the indoor environments, e.g. odour or special activities like dry cleaning, painting, printing, degrassing etc., it is recommended to undertake simultaneous ambient air measurements in order to trace respective pollutants.
— Supplementary information
An in-depth collection of typical information on indoor climate, activities etc. are less necessary.
However, a careful description of individual sampling sites and an investigation and description of the chemical nature of the material in the nearest neighbourhood of each sampling site are prerequisite to understanding the analytical results and to effective countermeasures if necessary.
7.3.6 Testing of effectiveness of remedial actions
The remedial actions for reducing indoor air pollution will consist of either the removal or modification of the source or improvement to the ventilation conditions. Such remedial actions are considered to the extent that pollutants have been identified and are used as indicators of their effectiveness.
Obviously, the most important feature of the measurement aimed at evaluating the effectiveness of remedial actions is that samples have to be collected before and after the remedial actions under identical or as much the same conditions as possible. This implies that the measurement strategy shall be chosen in such a way that the success or failure of the remedial actions is demonstrated as clearly as possible by the result of the measurement.
Notice that the success of the measurements for testing the effectiveness of remedial treatments depends on a critical and documented choice of the sampling conditions before the beginning of the remedial actions. The two samplings (before and after the actions) shall consider as an unity.
To test effectiveness of remedial actions the elements of sampling strategy shall be used as follows in addition to the basic information as given in 7.2.2 to 7.2.7:
— Time of sampling
For planning the sampling time care shall be taken of the identity of the sampling conditions which are not included in the remedial actions. Therefore these conditions (e.g. temperature, humidity and ventilation) shall be as similar as possible for both measurements. E.g., identical sampling conditions are not realised if one measurement takes place in the summer (high temperature, good ventilation, no room-heating) and the second measurement takes place in winter (low temperature, poor ventilation, room-heating).
The decay of the pollutants after removal or reduction of an emission source will govern the time of the second sampling event. If the decay is known the time of the second sampling event has to be scheduled beforehand. Otherwise successive samples have to be taken.
— Sampling duration and sampling frequency
For the selection of these parameters the type and objective of the remedial action has to be taken into consideration, however the sampling duration of both measurements shall be equal.
Diffusive sampling is particularly suitable for long-term sampling if the remedial action is aimed at reducing average concentrations or exposures. For short-term sampling aimed at assessing the effect of source modification or other actions to reduce peak concentrations of pollutants the diffusive sampling may be of limited value.
Duplicate sampling is recommended for optimal quality control because of the inherent juridical and financial consequences.
— Sampling sites
All sampling sites shall be chosen in order that measurements before and after the remedial action are possible at the same position and at the same height above the floor.
In principle air samples shall be collected in each indoor environment in which a remedial action is taken. If the same action is taken in a number of identical buildings or independent parts of buildings, for economical reasons, measurements may be performed only in a subset of them. However, investigators shall be aware that the "same" action may yield largely varying results for unexpected reasons such as human errors or unexpected inhomogeneity of materials. In any case a minimum of three or 10 % of the sites shall be selected randomly. Measurements at additional sites shall be performed after the remedial action if the measured mean pollutant concentrations are near to the maximum admissible or target concentrations aimed at by the remedial action, e.g. if the upper limit of the 95 % confidence interval of the measured mean concentrations are higher than the target concentrations.
Within an indoor environment all spaces in which a remedial action has been taken or which shall benefit from the remedial action shall in principle be included in the pollutant measurement program.
environments themselves. If a source is removed or modified which, although polluting several spaces, causes highest pollutant levels in a distinct space, measurements in this space may be sufficient.
In the case of the remedial action involving modification or removal of a source of pollutants, the source position is appropriate for assessing the result of the remedial action.
However, the breathing zone position (1 m to 2 m above the floor level) will be more appropriate if the remedial action is intended to significantly reduce occupant exposure to a pollutant which may have other possible sources in the environment.
If the remedial action is aimed at improving the ventilation efficiency at least two sampling positions in a space shall be selected which before the remedial action yield the largest pollutant concentration.
For other remedial actions the breathing zone position shall be considered.
— Simultaneous ambient air measurements
If the indoor air pollution is high due to ambient concentrations, parallel ambient air measurements are necessary both before and after the remedial actions to control the effectiveness of those actions.
If the ventilation conditions change, ambient air measurements are useful to describe the influence of ambient pollution on the indoor air concentrations.
— Supplementary information
Furthermore notice has to be taken of the following conditions provided that these conditions are not included in the remedial actions:
— use of the room;
— activities of the occupants (e.g. using of solvents and detergents, hobbies, renovations);
— use of fuels (wood, gas, oil, coal), kind and duration of heating;
— ambient sources and their variability (daily, weekly, seasonally).
— Uncertainty
These measurements require a high reproducibility because they are based on a critical comparison of the results before and after the remedial actions.
For testing of effectiveness of remedial treatments the requirements for the uncertainty are the same as 7.3.2. A calculation of the diffusion coefficients is also possible. If the measured mean pollutant concentration after the remedial action is near to the specified limit or guideline value a further measurement to check the observance of these values described in 7.3.4 is necessary.
7.3.7 Analysis of trends in indoor air quality
It is important to know trends of indoor air pollutants in order to understand the mechanisms of their occurrence [54] and to reconsider measures undertaken in the past to improve indoor air quality. This can be achieved by studying indoor air pollutants e.g. benzene, formaldehyde, tetrachloroethene, dichloromethane or other pollutants which had been regulated or discussed critically in the past. Also important is to recognise any appearance or increase of compounds which have been recently introduced in the indoor environment by new technologies and occupants behaviour or by substitution for other compounds of concern. In the UK a study has been undertaken of 860 homes in order to establish a baseline for concentrations of indoor air pollutants in order that the UK Government can evaluate trends in indoor air quality by undertaking repeat surveys at approximately 5 year intervals [55].
— Time of sampling
To rule out any seasonal effects the individual sampling events shall be evenly distributed throughout the year. The time of individual sampling shall be fixed in a way that representative concentration values can be assessed. However, for sampling of duration ≥ one week the settings of sampling time tend to be less important.
— Sampling duration and sampling frequency
The duration of sampling is less important providing that the limits of determination for all compounds of interest are exceeded and representativity is guaranteed. The frequency of one sampling per site within one study is quite sufficient. The long-term frequency of studies to investigate trends depends upon available resources. A frequency of one study per five years seems to be optimal.
— Sampling site and determinations with resolution in space
The sampling site shall be representative, e.g. the centre of the room most inhabited by all occupants shall be used.
— Simultaneous ambient air measurements
Simultaneous ambient measurements are not necessary.
— Supplementary information
The documentation of all conditions influencing the concentration of indoor air compounds by a standard questionnaire is a prerequisite to analyse trends. This will include indoor climatic parameters, activities and the introduction of new material and products into the indoor environment.
— Uncertainty
When analyzing long-term trends all aspects of quality control and quality assessment have to be addressed with a particular care. If comparing new data with historic data, it is important to relate the performance of the method previously used with that being applied in the new study. The trueness of all assessment procedures shall be as good as reasonably achievable and external intercomparison exercises, preferably at field conditions, shall be incorporated into the studies. If external intercomparison exercises don’t involve diffusive samplers but a reference method, a second intercomparison study can be used to compare the reference method with the diffusive sampling method used in the trend study. The repeatability shall be well documented and all QA/QC documentation of the level needed shall cover the total time frame of trend analysis.
7.3.8 Assessment of concentrations in indoor air at abnormal or "worst-case" conditions Most often there is a relationship between the source strength and the indoor environmental conditions.
The principle outcome of the application of a worst case measurement strategy may provide information about the nature of sources of indoor pollutants.
In addition to this diffusive samplers are especially useful to assess particular conditions, e.g. very low air exchange rates (e.g. building constructions aimed at low energy consumption) or strong sink effects (influence of special building material leading to large additional reduction of indoor air concentrations) or the reverse of it, the function of secondary sources (release of formerly adsorbed compounds) or the reactivity of special compounds indoors.
The respective results may lead to a recommendation to adjust unfavourable conditions to normal values [56] in order to maintain good indoor air quality prior to removal of material suspected to be a pollutant source which may incur substantial costs.
Most important, it shall be emphasized that the results of this sampling strategy shall not be used to assess possible health impairments at normal conditions.
To assess concentrations in indoor air at abnormal or "worst-case" conditions the elements of sampling strategy shall be used as follows in addition to the basic information as given in 7.2.2 to 7.2.7:
— Time of sampling
— Sampling duration and sampling frequency
The sampling duration is less important provided the limits of determination for all compounds of interest are exceeded. Sampling frequency is a matter of degree of success and/or the resource available
— Sampling site and determinations with resolution in space
The sampling site shall be standardized, e.g. in the centre of the room under investigation and not particularly influenced by emission sources.
— Simultaneous ambient air measurements
Simultaneous ambient air measurements will only provide information of background concentrations not related to special indoor environmental conditions. They are less necessary.
— Supplementary information
The prerequisite of a successful assessment is the control and/or at least the documentation of all conditions influencing the concentration of compounds in indoor air over the total of the sampling duration.
— Uncertainty
The uncertainty in terms of repeatability and trueness have to be well documented, but there is less requirement to maintain best values of both parameters as provided the statistical results to be discussed differentiate significantly from values at normal indoor conditions.
7.3.9 Personal monitoring
Personal monitoring is a very useful objective to get information of the direct burden of a person with regard to selected compounds [37,57,58]. In contrast to stationary diffusive sampling personal (mobile) samplers are usually exposed to much higher variations in air velocity, air temperature, humidity and CO2 concentrations. Personal samplers may be exposed to indoor, ambient and workplace air. To differentiate between distinct exposure situations the temporary use of personal samplers will be useful.
Hence one or several samplers have to be opened and closed according to the situation or a determined schedule. The increase of information will be beneficial but it shall be kept in mind that this multi sampling procedure is very complicated and therefore not recommended for a large collective.
To monitor personal exposure the elements of sampling strategy shall be used as follows in addition to the basic information as given in 7.2.2 to 7.2.7:
— Time of sampling
The sampling time is less important providing that specific situations and activities are of no concern.
— Sampling duration and sampling frequency
The duration of sampling is less important providing that the limits of determination for most compounds of interest are exceeded. The successive sampling which is a matter of resource available will provide information on variation of the personal exposure.
— Sampling site and determinations with resolution in space
The personal sampler shall be as close as possible to the inhaled air but not directly exposed to the expired air. It is favourable to fix the personal sampler to items of clothing below mouth and nose.
The position has to be recorded. During sleep and showering/bathing the personal sampler shall be placed nearby. The site shall be representative for inhaled air and not subject to local sources or sinks (open window, evaporating fluids, etc.)!
— Supplementary information
Parallel monitoring of air, temperature and humidity (e.g. by miniature data loggers) gives additional information to interpret results and to check reliability. Continuous daily records (time, site, activities, incidents, sources, etc.) shall be made in order to make the data from personal monitoring with
Table 1 – Example of a sampling protocol for personal monitoring Sampler type: ... Batch No.: ... Sample ID: ...…..
Indoor Ambient
Time Home Workplace Transfer Other Home Workplace Transfer Other
Remarks and additional information about site, sources and activities 0:00 -
0:30 - 1:00 - etc.
……
11:00 - 11:30 - etc.
……
23:00 - 23:30 -
— Simultaneous ambient air measurement
Usually simultaneous ambient air measurements are not necessary.
— Uncertainty
The uncertainty shall be as low as reasonably achievable. The results include additional components of uncertainty because of the change of location of the test person and unpredicted influences of the environment on the sampler. To minimise uncertainty of personal monitoring an extended information/training session and/or video demonstration is necessary. During the measuring period an opportunity for feedback to local advisors shall be provided.