Sampling time and sampling frequency
In this programme, airborne particulate matter is sampled twice-weekly at each sampling site. Duration of sampling is typically 24 hours. It is highly recommended that sampling always takes place at the same day of the week.
Generally, sampling on Monday and Thursday is recommended.
Typical sampling periods:
1. Monday – Tuesday, i.e. Monday 9 am to Tuesday 9 am
2. Thursday – Friday, i.e. Thursday 9 am to Friday 9 am
Note that the sampling time of 24 hours might not be appropriate at highly polluted areas.
In order to determine the sampling period, the following procedure is recommended:
(a) Sample one week for 24 hours and weigh filters. If weight change < 1 mg, continue to sample for 24 hours from now on otherwise change sampling regime to (b).
(b) Change 24 hour sampling period to 2 hours on and 2 hours off. This results in a total sampling time of 12 hours. Sample again for one week. Weigh filters. If weight change is < 1 mg, continue to sample from now on using this 12 hour sampling regime that runs for 24 hours. If weight change is still > 1 mg, change sampling regime to (c)
(c) Change 24 hour sampling period to 1 hour on, 2 hours off. This results in a total sampling time of 8 hours over a 24 hour period. Again, sample for one week and measure the exposed filters. If weight is < 1 mg, continue to sample using this sample regime. If weight change is still > 1 mg, continue to decrease the sampling time until weight change < 1 mg is achieved.
Note that the flow rates are important. For the statistical analysis, the cut off point should be around 12 l/min, i.e. all filters that have been collected with flow rates below 12 l/min should be discarded.
Note that regular sampling should commence only after the site depended sampling regime has been established. If the sampler is moved to a new location, the air particulate matter pollution may have changed significantly. A new sampling protocol has to be established following the procedure (a) – (c).
2.4.1 Characteristics of a clean air site
In remote regions and rural areas the air can be very clean. The PM10 particle mass concentration can be less than 10 – 15 μg/m3. PM10 comprises of both coarse and fine fractions. In these regions, it is recommended to extend the sampling period for a two-day period. In this programme, New Zealand chose a two-day sampling period in the remote location of Barring Head, for example.
2.4.2 Characteristics of a highly polluted air site
In highly polluted regions, a sampling period of 24 hours may not be achievable. This can be easily checked by monitoring the drop in rotameter flow rate. With the WHILEY valve fully open, the flow rate will be 16-17 lpm at the start of the sampling. Sampling should proceed until the flow rate is reduced to about 14 lpm. This may result in sampling period of much less than 24 hours. If the sampling period can only be up to 8-10 hours (refer to 2.7), then it is recommended to sample two filters per day, i.e. one filter during day-time and another filter during night time or to use the procedure under 2.4b,c.
Loading of loaded stacked filter cassette into black polyethylene container
Firstly, the fine and coarse filters have to be loaded into the spare stacked filter cassette (for details refer to section 2.5). Figure 8 shows an image of the SFU inserted in stacked filter cassette.
Sampling time and sampling frequency
In this programme, airborne particulate matter is sampled twice-weekly at each sampling site. Duration of sampling is typically 24 hours. It is highly recommended that sampling always takes place at the same day of the week.
Generally, sampling on Monday and Thursday is recommended.
Typical sampling periods:
1. Monday – Tuesday, i.e. Monday 9 am to Tuesday 9 am
2. Thursday – Friday, i.e. Thursday 9 am to Friday 9 am
Note that the sampling time of 24 hours might not be appropriate at highly polluted areas.
In order to determine the sampling period, the following procedure is recommended:
(a) Sample one week for 24 hours and weigh filters. If weight change < 1 mg, continue to sample for 24 hours from now on otherwise change sampling regime to (b).
(b) Change 24 hour sampling period to 2 hours on and 2 hours off. This results in a total sampling time of 12 hours. Sample again for one week. Weigh filters. If weight change is < 1 mg, continue to sample from now on using this 12 hour sampling regime that runs for 24 hours. If weight change is still > 1 mg, change sampling regime to (c)
(c) Change 24 hour sampling period to 1 hour on, 2 hours off. This results in a total sampling time of 8 hours over a 24 hour period. Again, sample for one week and measure the exposed filters. If weight is < 1 mg, continue to sample using this sample regime. If weight change is still > 1 mg, continue to decrease the sampling time until weight change < 1 mg is achieved.
Note that the flow rates are important. For the statistical analysis, the cut off point should be around 12 l/min, i.e. all filters that have been collected with flow rates below 12 l/min should be discarded.
Note that regular sampling should commence only after the site depended sampling regime has been established. If the sampler is moved to a new location, the air particulate matter pollution may have changed significantly. A new sampling protocol has to be established following the procedure (a) – (c).
2.4.1 Characteristics of a clean air site
In remote regions and rural areas the air can be very clean. The PM10 particle mass concentration can be less than 10 – 15 μg/m3. PM10 comprises of both coarse and fine fractions. In these regions, it is recommended to extend the sampling period for a two-day period. In this programme, New Zealand chose a two-day sampling period in the remote location of Barring Head, for example.
2.4.2 Characteristics of a highly polluted air site
In highly polluted regions, a sampling period of 24 hours may not be achievable. This can be easily checked by monitoring the drop in rotameter flow rate. With the WHILEY valve fully open, the flow rate will be 16-17 lpm at the start of the sampling. Sampling should proceed until the flow rate is reduced to about 14 lpm. This may result in sampling period of much less than 24 hours. If the sampling period can only be up to 8-10 hours (refer to 2.7), then it is recommended to sample two filters per day, i.e. one filter during day-time and another filter during night time or to use the procedure under 2.4b,c.
Loading of loaded stacked filter cassette into black polyethylene container
Firstly, the fine and coarse filters have to be loaded into the spare stacked filter cassette (for details refer to section 2.5). Figure 8 shows an image of the SFU inserted in stacked filter cassette.
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