Assessing Ambient Air Quality Using the MiniVol TAS Air Sampler
***This Procedure is for Training Purposes Only***
Day One (Monday)
1. Review objectives, background information and procedures
2. Complete the Field Checklist
3. Identify one group member for each of the following tasks so that each person in the group has at least one chance to handle the filters and/or sampler:
Filter weighing (pre): / Filter unloading:Filter loading: / Sampler data retrieval:
Sampler programming: / Filter weighing (post):
Objectives
Participants will:
· Gain experience in collection & measurement of airborne particulates;
· Keep a detailed Field Data Sheet over a period of several days;
· Be able to explain how the MiniVol sampler works;
· Understand that external conditions (weather, filter handling, etc.) can influence the sampling;
· Calculate the ambient air concentration of PM10 or PM2.5 in a 24-hour period.
Background Information
In some areas, suspended particulate matter is the most significant contributor to air pollution. Mass concentration is defined as the total mass of particulate matter per volume of air, usually expressed in micrograms per cubic meter (µg/m3). Measurements can include all particles with a mean diameter of 10 micrometers or smaller (PM10) or 2.5 micrometers or smaller (PM2.5).
Several methods exist that will quantify the total amount of particulate matter (PM) in ambient air. One method uses the MiniVol sampler. The MiniVol consists of a vacuum pump that is calibrated to draw in a fixed volume of air at approximately 5.0 liters per minute (L/min). Air is drawn through a particle size separator and then through a filter which acts as a barrier to particles. MiniVols typically use quartz-fiber filters for capturing PM10 and Teflon filters for PM2.5. Particle size separation is achieved by impaction. The average concentration of PM per cubic meter of air can be calculated by weighing a dried filter before and after the sampling run, and correlating the particulate weight to the volume of air drawn through the pump.
Quality Control
When conducting any type of monitoring or sampling, there should be some quality control (QC) measures in place to ensure data quality. Students will be introduced to two QC measures: field checklists and field blanks. Field checklists help ensure that all supplies needed in the field are in-hand. Sometimes, a site can be far away from the program’s office, and it is not feasible to simply run back to the office when supplies are forgotten. Field blanks are filters that are exposed to all of the same conditions and procedures as the filter, except actual exposure (i.e. sampler will not be turned on when field blank is loaded). This helps to ensure that all handling procedures are followed according to protocol and are not introducing error into the process.
Filter handling
The filters are very sensitive and can easily tear, be punctured, or absorb ambient moisture or oils from skin, all of which will impact the final mass of the filter. Prior to and following the sampling event, filters must be equilibrated (stabilized) in a desiccating (drying) chamber for at least 24 hours, which will absorb ambient moisture absorbed by the filter during storage and sampling. Filters should be handled by using forceps to grab the plastic-ringed edge, and by wearing protective gloves as a secondary precaution. The person wearing gloves should be careful not to touch anything except for the filter and/or forceps at all times, and also be careful not to drop the filter. Filters should be transported in a static-free plastic bag housed in a cooler with an ice pack so that the filter is not exposed to excessive heat and is protected from contamination and static electricity. Any incidents related to filter handling should be documented.
Day Two (Tuesday) – Initial Equilibration
In the lab:
1. Prepare a weighing pan to hold the filter during equilibration.
2. Carefully take a filter from the package and inspect for tears, marks, or other anomalies; place it in the weighing pan.
3. Record the filter number on your field data sheet.
4. Open the desiccator cabinet and insert the weighing pan containing the filter.
5. Repeat the above steps for your field blank.
6. Close the desiccator cabinet and record the initial equilibration time and relative humidity (RH) of the cabinet.
In the classroom:
- Plug in the MiniVol Battery so it can charge at least 12 hours
Day Three (Wednesday) – Initial Weighing & Start Sampler
In the lab:
1. Filters must be weighed on a microbalance with significant digits to 0.0001 grams.
2. Make sure the inside of the microbalance is clean and zeroed out.
3. To clean, wipe with a static and lint-free wipe such as a Kimwipe
4. To zero, press and hold the TARE button until the display reads 0.0000)
5. Remove the weighing pan containing the filter from the desiccator and carry it to the weighing room.
6. Slide open the side door of the microbalance enclosure.
7. Carefully remove the filter from the weighing pan and place the filter onto the microbalance pan.
8. Close the microbalance door and allow the digital reading to stabilize.
9. This is your pre-weight; record the value on your data sheet, along with the current date and time.
10. Prepare the filter cassette by separating the two halves of the cassette and removing the storage blank.
11. Open the door of the balance and remove the filter from the enclosure using forceps.
12. Carefully place on top of the support screen in the bottom half of the filter cassette.
13. Place the top half of the filter cassette onto the bottom half and reconnect firmly.
14. Put the filter cassette in a plastic bag for transport to the monitoring site.
15. Repeat the above steps for your field blank.
At the monitoring site:
1. Find a location for the sampler ensuring it is upright and at least 30 cm from any obstacles to air flow.
2. Open the sampler and secure the battery in the battery slot; ensure the connection jack at the top of the slot is matched with the battery connection (note battery number on your Field Data Sheet). Ensure the storage filter is in place.
3. To obtain the beginning flow rate, press the [on/auto/off] button twice to start the pump. On the display, a horizontal indicator line should be above the word “on.” (NOTE: if your LCD panel does not have any display, you need to replace the AA battery).
4. Wait approximately 30 seconds to allow the flow rate to stabilize then record the reading on your Field Data Sheet. The flow rate should be as close to 5 L/min as possible; adjust the flow by turning the flow adjust knob. Gauge the flow rate to the nearest tenth of a liter using the center of the ball for the reading. (If the flow meter indicates zero or a very low reading, try pressing the [reset] button. If the flow still does not stabilize, see instructor for assistance.)
5. Press the [on/auto/off] button twice to stop the pump.
6. Remove the field blank filter cassette from the plastic bag and insert it into the filter assembly. Remove the field blank cassette from the filter assembly and replace it in its bag; keep it with you when you return to the classroom. Proceed through the following steps with your run filter.
7. Insert the run filter cassette into the filter holder assembly and attach to the quick connect inlet located on the top of the MiniVol sampler.
8. Press the [on/auto/off] button once to set the timer to the “auto” mode.
9. Confirm that the correct local time is displayed on the screen. If not, see instructor for assistance.
10. To set the timer, press the [prog] button once. 1on will appear near the lower left corner of the display indicating that the power-on time for the first cycle is ready to be programmed.
11. Press the [hour] and [min] buttons to enter the power-on time for the first cycle (give yourself about 10 minutes to complete the remaining steps before the sampler turns on).
12. Press the [week] button to select the desired day. NOTE: When more than one day is displayed, it means you are programming the sampler to have the same power-on time for all days. Be careful to choose just one day.
13. After you have entered the power-on time and date for the first cycle, press the [prog] button once. 1off now appears on the display to indicate that the power-off time for the first cycle is ready to be programmed.
14. Press the [hour] and [min] buttons to enter the power-off time.
15. Press the [week] button to select desired day; be sure not to select the same day as the power-on day.
16. Press the [clock] button to return to the real-time clock display. Double-check that the display still indicates “auto” (with a horizontal indicator line above it).
17. Record the following information on your Field Data Sheet (NOTE: you will be given the meteorological data when you return to the classroom):
§ MiniVol sampler serial number (SN)
§ Start Time and Date
§ Elapsed Time (beginning) – small counter located above programmable timer assembly
§ Note field observations at site (clear skies, clouds, rain/snow, smoke, filter handling notes, or other observations at the site that could impact sampling)
18. Close the sampler door and secure the latches.
Day Four (Thursday) – Sample Collection & Final Equilibration
At the monitoring site:
1. Check if the MiniVol has completed its sampling run. If not, wait for the sampling run to end (unless otherwise instructed).
2. Open the sampler door and check the control panel for any error lights.
3. Verify the correct time and day of week on the display.
4. To obtain the ending flow rate press the [on/auto/off] button once to start the pump.
5. Allow the flow rate to stabilize for approximately 30 seconds then record your reading on the Field Data Sheet. Gauge flow rate to the nearest tenth of a liter using the center of the ball for the reading.
6. Press the [on/auto/off] button twice to stop the pump.
7. Record the following information on your Field Data Sheet (NOTE: you will be given the meteorological data when you return to the classroom):
§ End Time and Date
§ Elapsed Time (ending) – small counter located above timer assembly
§ Note field observations at site (clear skies, clouds, rain/snow, smoke, filter handling notes, or other observations at the site that could impact sampling)
8. Close the sampler door and secure the latches.
9. Disconnect the filter holder assembly from the MiniVol quick connect inlet and put the filter cassette into the plastic bag for transport back to the laboratory.
10. Using your field blank filter, place the filter cassette into the filter holder assembly, close the MiniVol and then re-open it and remove the field blank. Return the filter to its plastic bag.
In the lab:
1. Prepare a clean weighing pan to hold the filter.
2. Open the filter cassette and carefully move the filter from the cassette to the weighing pan.
3. Place the weighing pan and filter into the desiccator cabinet and close the door.
4. Record the date and time for final equilibration start.
5. Repeat the above steps for your field blank.
6. Replace the storage blank in the filter cassette and place cassette in the filter holder assembly.
Day Five (Friday) – Final Weighing & Calculate PM Concentration
In the lab:
1. Make sure the inside of the microbalance is clean and zeroed out.
a. To clean, wipe with a static and lint-free wipe such as a Kimwipe
b. To zero, press and hold the TARE button until the display reads 0.0000)
2. Remove the weighing pan containing the filter from the desiccator and carry it to the weighing room.
3. Slide open the side door of the microbalance enclosure.
4. Carefully remove the filter from the weighing pan and place the filter onto the microbalance pan.
5. Close the microbalance door and allow the digital reading to stabilize.
6. This is your post-weight; record the value on your data sheet, along with the current date and time.
7. Remove the filter from the microbalance and discard.
8. Repeat the above steps for your field blank.
In the classroom:
1. Complete any missing information on your Field Data Sheet.
2. Work through the calculations of ambient PM concentration for run filter only; you can only calculate the difference in mass for the field blank. (see next page).
Questions/Discussion
1. Why must the filter be dried before weighing it?
2. How could weather have affected the measurement?
3. Did your quality control (field blank) indicate any issues with filter handling?
4. What other factors might affect the measurement?
Revised: 6/2/14