AIR POLLUTION MONITORING LABORATORY
CIVE/BSEN 327 (30-40 students; lab used since mid-1990s)
University of Nebraska-Lincoln
Dr. Bruce Dvorak, Environmental Engineering
Dr. Dennis Schulte, Biological Systems Engineering
Received 12 November 2008

References:
1.	Wright, G.D. (1994) Fundamentals of Air Sampling, Lewis Publishers, Bota Raton, FL. 
2.	Masters, Gilbert M. (1991) Introduction to Environmental Engineering and Science, Prentice Hall, Upper Saddle River, NJ.
3.	Sincero, Arcadio P. and Gregoria A. Sincero (1996) Environmental Engineering - a Design Approach, Prentice Hall, Upper Saddle River, NJ.
4.	Selected Physical and Chemical Standard Methods for Students, American Public Health Association, 17th ed., pp 432-440.
5.	Vesilind, Introduction to Environmental Engineering, PWS Publishing, First Edition, 1997. pp. 206-215
6. Davis, M.L. and D.A. Cornwell. (2007). Introduction to Environmental Engineering. 4th Edition. McGraw Hill, Inc.

Purpose:  To become familiar with the measurement of particulates in the air and to gain experience in designing an experiment for obtaining environmental data.

TENTATIVE SCHEDULE:

During Lab:	Discuss the use of air monitors.
		Discuss experimental design (talk with TA or instructor about your design).
		Estimate your minimum sampling time before leaving the lab.
		Students will sign-up for a time to check out the air monitors

At time that you check out air monitor:
	obtain the tare mass of the filter.

Return the air monitor at the arranged time:
	put filter in 105C oven for 1 hour.
	obtain the final dried mass of the filter.

Prepare your lab report.

Note: 	Each monitoring device costs around $900.  Although the equipment is durable, take care not to damage the equipment.  Also do not leave the monitoring equipment unattended.  

General Theory:

In this lab, a personal particulate sampler will be used to measure PM10 (particulate matter of a size less than 10 m), and total particulate.  For many situations, this sampler can approximately measure the amount of air pollutant an individual has inhaled.  This measurement is obtained with an air flow pump, which simulates breathing, and a quartz filter which indicates the amount of trapped particulate.  Separate filters are used to trap different size particles.  In this lab we use two - one to capture particles larger than 10 mm and a second to cat all particles that passed trough the first filter.  The particulate captured on the second filter is used to measure PM10.  The particulate captured on both filters is used to measure total particulate. These samplers can also be used to sample for lead if a glass fiber filter is used.

Various Ambient Air Quality Standards for criteria pollutants:

		USA Federal	California	European Community	
Pollutant	Average Time	EPA (mg/m3)	(mg/m3)	Directives (mg/m3)	
Particulates (PM-2.5	Annual	15			
Particulates (PM-2.5	24 hour	35			
Particulates (PM-10)	24 hour	150	50	250	
	Annual		30	80	
Total Particulates*	24 hour	260*	 --	 --	
	Annual	75*	 --	 --	
*  EPA recently removed Total Particulates from the NAAQS.  However we will keep the former values here for reference.

In addition to outdoor standards, exposure guidelines of indoor air pollutants (Sincero and Sincero, 1996) are given:

	Inhalable (total) particulate matter:	150-350 mg/m3	(24 hours)
						55-110 mg/m3		(Annual)

For regulatory purposes, particulate is typically measured with a different type of sampler.  A high-volume sampler operates in a similar fashion to the portable particulate sampler used for this lab.  This high volume sampler is about 5 feet high and weighs over 100 pounds.  Thus, the equipment is rarely moved once installed at a particular location.

Background on Particulate Matter 

Atmospheric particulate matter is defined to be any dispersed matter, solid or liquid, in which the individual aggregates are larger than single small molecules (about 0.0002 m in diameter), but smaller than about 500 m.  As a category of criteria pollutant, particulate matter is extremely diverse and complex, since size and chemical composition, as well as atmospheric concentration, are important characteristics.

A number of terms are used to categorize particulate, depending on their size and phase (liquid or solid).  The most general term is aerosol, which applies to any tiny particles, liquid or solid, dispersed in the atmosphere.  Solid particles are called dusts if they are caused by grinding or crushing operations.  Solid particles are called fumes if they are formed when vapors condense.  Liquid particles may be called mist or, more loosely, fog.  Smoke and soot are terms used to describe particles composed primarily of carbon that result from incomplete combustion. Smog is a term that was derived from smoke and fog, originally referring to particulate matter, but now describing air pollution in general.

Although particles may have very irregular shapes, their size can be described by an equivalent aerodynamic diameter determined by comparing them with perfect spheres having the same settling velocity.  The particles of most interest have aerodynamic diameters in the range of 0.1 to 10 m (roughly the size of bacteria).  Particles smaller than these undergo random (Brownian) motion and, through coagulation, generally grow to sizes larger than 0.1 m.  Particles larger than 10 m settle quite quickly.  A 10-m particle, for example, has a settling velocity of approximately 20 cm/min.

The ability of the human respiratory system to defend itself against particulate matter is, to a large extent, determined by the size of the particles.  The upper respiratory system consists of the nasal cavity and the trachea, while the lower respiratory system consists of the bronchial tubes and the lungs themselves.  Each bronchus divides over and over again into smaller and smaller branches, terminating with a large number of tiny air sacs called alveoli.

Large particles that enter the respiratory system can be trapped by the hairs and lining of the nose.  Once captured, they can be driven out by a cough or sneeze.  Smaller particles that make it into the tracheobronchial system can be captured by mucus, worked back to the throat by tiny hair like cilia, and removed by swallowing or spitting.  Particles larger than about 10 m are quite effectively removed in the upper respiratory system by these defense mechanisms.  Smaller particles, however, are often able to traverse the many turns and bends in the upper respiratory system without being captured on the mucous lining.  These particles may make it into the lungs, but depending on their size, they may or may not be deposited there.  Some particles are so small that they tend to follow the air stream into the lungs and then right back out again.  Particles roughly between 0.5 and 10 m may be small enough to reach the lung, and large enough to be deposited there by sedimentation.  Sedimentation is most effective for particles between 2 and 4 m.

The original NAAQS (National Ambient Air Quality Standards) for particulates did not take size into account.  Larger particles could dominate the weight per unit volume measure, but be unimportant in terms of human health risk.  With the PM-10 standard promulgated in 1987, however, only particles smaller than 10 m, which are capable of reaching the lungs, are measured.

Elevated particulate concentrations in the atmosphere, especially in conjunction with oxides of sulfur, have been linked to rises in the number of hospital visits for upper respiratory infections, cardiac disorders, bronchitis, asthma, pneumonia, emphysema, and the like.  In addition, some particulates are especially dangerous because of their toxicity.  Many carbonaceous particles, especially those containing polycyclic aromatic hydrocarbons (PAHs), are suspected carcinogens.

Particulate emissions have decreased substantially in the past few decades.  As Figure 1 shows, particulate emissions in 1950 were estimated to be about 25 million metric tons, while in 1986 they were about 7 million tons.  Reductions between 1940 and 1970 were due more to the replacement of coal-burning locomotives and fewer forest wildfires than to any particular change

Figure 1.  Trends in particulate emissions, 1940-1986.

in emissions from fuel combustion.  However, since the Clean Air Act of 1970, tremendous reductions in combustion emissions have been achieved, especially by the electric utilities.  In 1970 utilities burned 320 million tons of coal, releasing 2.3 million tons of particulate.  In 1986, 685 million tons of coal were burned and only 0.4 million tons of particulate were emitted.

Experimental Design:

Each group must prepare a section in the lab report which explains how the following steps were used to design their experiment.  This section will be several paragraphs long.  In addition, groups are encouraged to check with the TA if there is uncertainty as to whether assumptions made are satisfactory.  Unreasonable assumptions may result in loss of points.  Moreover, it is important to divide the work evenly among group members, i.e. if one person samples, the others should obtain weight measurements, etc.

The lab procedure steps are as follows:

  1)  	Consider the options and choose a situation in which the air quality can be measured.  	Examples include:
		Indoor air quality:
			  Second hand smoke
			  Particulate exposure at work 
				(e.g. dust from sanding sheet rock, moving bales of hay in a barn)
			  Particulate exposure at home 
				(e.g. dust coming out of an old furnace vent)
			  Particulate exposure at school
				(e.g. working on the concrete canoe)

		Outdoor air quality:		
			  Particulate exposure at work 
				(e.g. dust from plowing a field)
			  Outdoor activities 
				(e.g. camping next to a fire)  

	*  Note - it is possible (and likely more interesting) for groups to work together in 	developing an experiment.  Each group can test a different set of conditions pertaining to 	the same situation.  For example, one group may spend time in the smoking section of a 	restaurant and another may spend time in the non-smoking section.  Although groups 	may share data, lab reports must be prepared separately.

2. Make an estimate of the expected air quality (Total particulate).

	The following situations give a general idea of expected air quality:

	 Ambient outdoor air quality in Nebraska is typically between 10 and 30 g/m3 of air. 	     For example, the particulate matter in the air on the roof of Walter Scott Engineering Center on Dec. 3, 1996 was 10 g/m3 of air.

	  Indoor air quality in a smoky room is typically between 500 and 3500 g/m3 of air.

	  If you feel lung irritation (from particulate), then the particulate concentration is often over 500 g/m3 of air. 

For sampling ideas and example concentrations, see the table on the handout page that contains results from previous classes.

Handout a representative copy of data from a previous year.

3. Determine an appropriate sampling time for the expected total particulate concentration.  Check to be sure your sampling time will yield a result above the method detection limit (MDL).

Method Detection Limits:

For each analysis method, there is a lower limit to the concentration that can be accurately measured.  It is possible to have a very low enough concentration of a parameter (i.e. BOD), which is below our ability to measure it.  These circumstances give rise to the concept of Method Detection Limit. 

The MDL is the lowest concentration level that can be accurately measured by an experienced analyst using well-calibrated instruments.  The MDL is typically determined by performing a statistical analysis on the results of a testing series of very low concentration samples.  This method is described further on pages 20 and 21 of the student version of Standard Methods. 

For this laboratory, we will approximate an MDL for each analysis.  To determine the MDL, find the lowest concentration that can be accurately measured.  In finding this concentration, use the following assumptions:

	Assume an average air flow rate of 2.7 L/ min.  This is the air flow rate required to capture particles larger than 10 mm on the first of the two filters.  Do not select a different flow rate.  A different flow rate will change the particle size captured on the first filter.

	The amount of particulate is measured by determining the difference in the mass of the final and initial dried filter.  For your experimental design, assume that the minimum difference in mass of the filter (between initial and final) that is significant (not due to random error) is 0.00007 g.  A large change in filter weight is preferred. 

	The only acceptable situation in which an experiment may be designed to have a filter mass   change of less than 0.00007 g is if the experiment is the “control” test that one group performs as a part of a multi-group collaboration. (e.g., one group tests the smoking section of a restaurant and another group tests the non-smoking section.) 

	The samplers will only run for 10-12 hours before the battery requires recharging.  If your experiment requires a sampling time greater than 8-12 hours, talk with the TA to make arrangements to take a charger with you.

The following equation can be used to determine the MDL by using the combined mass of both filters:

Make sure that the anticipated air concentration (for total particulate) is greater than the MDL (for total particulate) for your experiment.  If your MDL is greater than your anticipated air concentration, you will not be able to accurately measure the air quality.  The only way to decrease your MDL is to increase your sampling time.

Note:	If a total particulate or PM10 concentration is below the calculated MDL, report the resulting concentration as “less than MDL.”

General Procedure for Using Personal Air Monitors:

Prior to sampling, the filters for the pumps should be loaded in lab with the help of the TA.

1)  Take the filter from the 105C oven.  Be sure that the filters are fresh from the oven.  Do not use filters that have been sitting in a desiccator for an unknown amount of time; moisture can seep onto the filters while in a desiccator, especially when the desiccator’s cover has been removed.

2)  Transport the filters in a desiccator to the balance.

3)  Obtain a tare weight (initial dry mass) of each filter using the analytical balances.  Record the mass on the data sheet.

4)  Load filter as demonstrated by the TA into the filter cartridge.  
	  Make sure the filters are seated correctly and that all O-rings are sealed tightly.  (Your results will be skewed if the seals are not tight!)
	  Also make sure that the elongated holes in the filter line up with the holes in the plates.  If they are not lined up correctly, air cannot pass through.  See drawing below:

5)  Turn the pump on when you start to sample the air quality.

The procedure for operating the pump is as follows:

a)  Press ON/OFF button until the RUN/ HOLD LED lights up. (This often takes several seconds.)

		The Flow Fault and Low Bat LEDs will then light.  During the time these LEDs are being lighted, a number from 0 to 999 will be displayed.  This is the total number of the pump’s operating hours since its last calibration.

		When all three LEDs are lighted, the display will change to 8.88 LPM/MINS to show that all segments are functional.

		The pump will then begin operation.  The LOW BAT LED will be dark.  The flow fault light will be dark when the flow rate is within 0.1 LPM of the setpoint.

b)  Wait for 1 - 2 minutes after the pump has started (you will hear it operating).  If the pump is not showing the desired flow rate of 2.7 LPM, then adjust the flow rate settings using the  and  buttons.  

	* Note - the actual flow rate will not be 2.7 exactly.  While the pump is in use the numbers will vary within  0.1 LPM.

c)  The RUN/ HOLD button may be pressed to interrupt sampling without causing the timer to reset to zero.  This allows the user to sample the air intermittently.  The user may turn the pump on for a few minutes, pause the pump, and then restart the pump when ready to continue sampling the air.

d)  Press the ON/ OFF button at the end of sampling.  Press and hold the ON/OFF button until the sampler turns off (this takes several seconds).  The total sample minutes will be on the display and will remain until the pump is turned ON again.

Lab TA Note:  Problems can arise when the holes in the filter holders become plugged by particulates and the pumps “shut down.”  The screen on the pump will say “flow fault.”  Students are confused by this.  Thus, prior to sending them out with their apparatus, describe to them what the pump does when air flow to pump is restricted.  Tell them that if this happens, the flow of air probably has been restricted because the holes have become plugged with too much sample - and they should bring the monitor back to the lab .... and talk with the TA about repeating the setup.

6)  Be sure to record the number of minutes the pump has operated on the data sheet immediately after the pump is turned off (when you have finished sampling).  If you do not record the sampling time immediately, you risk losing the sampling time data if the battery gets low or if a button is pushed inadvertently.  Avoid placing the filter apparatus on its side after completing the monitoring; putting the apparatus on its side may lead some of the captured particulate to fall off of the filter.

7)  Take the monitor to the lab and, with the TA’s help, unload the two filters.  Be careful not to shake the filters or to turn them upside down.

8)  Place each filter in separate aluminum pans.  Mark the pans so you do not get the two mixed up.  

9)  Put the aluminum pans containing the filters in the 105C oven for 1 hour.  (They may be left for more than an hour.)

10)  Remove the pans and filters from the oven and place them in a desiccator.

11)  Weigh each filter using an analytical balance to determine the final dry mass.  Record the mass on the data sheet.

Data Analysis:
1)	Describe the exact sampling conditions.  A detailed list of many of the conditions that should be documented is given on the data sheet.

2) 	Determine the MDL (in units of g/m3) for each sample.  To find this value, select the minimum difference in filter mass that you feel is significant.  Be sure to report this value and provide a sentence or two of justification.  This “minimum significant difference in filter mass” represents the smallest change in the filter mass that you are confident is real and is not possibly due to small random errors.  Random errors can be related to inaccuracies in the balances (the last significant figure varies while you watch it) and moisture getting on the filters during the weighing process.  Observe the variations in the mass shown on the balance while you obtain your filter masses;  these variations will help you decide on and justify a “minimum significant difference.”

3)	Determine the total particulate and PM10 (in units of g/m3) for each sample.  If the concentration is below the MDL, be sure to report that value.

	To determine the PM10 concentration, use the mass captured on the stage 8 filter.  This represents particles that have were not captured on stage 3, which catches particles larger than 10 mm in diameter.  To determine the total particle concentration, use the difference in the filter masses of both filters (e.g., the total mass of particulate captured).  Use the equations below to determine the particle concentrations.

Stage	Initial Weight, W1	Final Weight, W2	Particulate Weight, W	Concentration, C	
	(grams)	(grams)	(grams)	(g/m3)	
3					
8					

	V = Volume of air sampled (m3)
		{Time in minutes, V in m3}

		{W in grams}

		{C in mg/m3}
4)	In addition to your own group’s data, determine the PM10, total particulate, and MDL for the following experiments which have previously been conducted in CIVE/BSEN 327:
 
Experiment #1
Stage	Initial Weight, W1 (g)	Final Weight, W2 (g)	
3 (captures particles > 10 mm)	0.04662	0.04743	
8 (captures particles < 10 mm)	0.04671	0.04934	

Sampling Time:  60 minutes
Sampling Location:  House being remodeled in southern Lancaster country
Sampling time (date and hours): 9-10 p.m., 11/9/97
Particulate Source:  Dust from sanding of sheet rock mud as it was swept during the cleaning.

Experiment #2
Stage	Initial Weight, W1 (g)	Final Weight, W2 (g)	
3 (captures particles > 10 mm)	0.04662	0.04743	
8 (captures particles < 10 mm s)	0.04671	0.04945	

Sampling Time:  52 minutes
Sampling Location:  Dinning room being remodeled in Lincoln
Sampling time (date and hours): 10-11 p.m., 11/11/97
Particulate Source:  Dust from sanding plaster walls as they are prepared for painting.

5)	Report the total particulate, PM10, and MDL values for your experiment and for the data provided in Step #4 in a well designed table.  Also report the minimum mass that your group considers to be significant.

Do not forget to put together a one or two paragraph explanation of how you obtained by minimum sampling time.  See the experimental design section for more description of this required section.

Questions:

1. What are the appropriate regulatory standard or recommended standard for this air quality that you tested?

2. Do(es) the sample(s) your group(s) tested surpass the regulatory / recommended standards for your sample? 

3.	Do you recommend any safety steps for humans exposed to the source of particle you sampled as well as for the data that you were supplied with in the handout?  Wearing dust masks?  Avoiding exposure altogether?  Justify your recommendation for each sample.

4. Why are airborne particulate a health risk for humans?

5. Why is PM10 used as a criteria pollutant instead of total particulate?

6. If you are told that a sample’s concentration is below the MDL, what do you know about the exact concentration of the sample (in what range will the exact concentration be)?

7. If you were to perform your experiment again, what (if anything) would you do to improve the accuracy of your experimental design?

Air Monitoring Data Sheet

Group Name & Number: ______________________________
Section #: ______________________
Dates for lab: ______________________
Names of group members: 		____________________________________________
			____________________________________________

Stage	Initial Weight, W1	Pan	Final Weight, W2	Particulate Weight, W	
	(grams)	No.	(grams)	(grams)	
3 (captures particles > 10 mm)					
8 (captures particles < 10 mm)					

Sampling Time: ___________ minutes

Sampling Location: ____________________
Sampling time (date and hours): _______________
Notes concerning the conditions at sampling location: 
	suspected source of particles
	visual appearance of air quality
	smell of air
	weather conditions,
	if the air made you feel like coughing or caused lung irritation
	number of people in area
	what people at that location were doing
	other notes