For Presentation at the Air & Waste Management Association's 91st Annual Meeting & Exhibition, June 14-18, 1998, San Diego, California

EPA SATURATION MONITOR REPOSITORY 98-TA31A.04

Kenneth Jones TRC Environmental Corporation, 6340 Quadrangle Drive, Suite 200, Chapel Hill, NC 27514
Neil Berg U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, Research Triangle Park, NC 27711
Stan Sleva and Susan Murchie TRC Environmental Corporation, 6340 Quadrangle Drive, Suite 200, Chapel Hill, NC 27514

ABSTRACT
This paper presents a summary of the U.S. Environmental Protection Agency's (EPA's) saturation monitor repository (SMR) and describes completed, ongoing, and planned studies, including the types of special filter analysis available. Saturation monitors are non-reference or non-equivalent sampling methods for measuring particulate matter (PM), carbon monoxide (CO), and nitrogen oxides (NOx ). The samplers are small, portable, and relatively easy to set up and operate. Because of their relatively low cost and ease of operation, it is customary to "saturate" a geographical area with the samplers to assess the air quality in areas where high concentrations of pollutants are possible. The data collected are helpful to control agencies in evaluating their ambient air monitoring networks for consistency with the 40 CFR Part 58 air quality surveillance regulations.

The SMR, which was established by EPA in 1993, includes a supply of saturation samplers and support equipment which agencies may borrow to conduct special field studies. The SMR also provides limited services to quality assure the samplers and assist in field studies upon request. Occasionally, State, local, and tribal agencies measure concentrations of particulate matter that exceed or are close to exceeding the national ambient air quality standards (NAAQS) for PM10 and/or PM2.5. In order to understand the nature of the particulate matter contributing to the high concentrations, EPA provides filter analysis service as part of the SMR to agencies requesting such assistance.

INTRODUCTION
The EPA encourages State and local air pollution control agencies to conduct short-term, multi-site ambient air pollutant monitoring studies using the technique known as saturation monitoring. Saturation monitors are non-reference or non-equivalent sampling methods for measuring PM, CO, and NOx. The samplers are small, lightweight, battery operated, rugged, weatherproof, portable, and relatively easy to set up and operate. Because they are comparatively inexpensive, easily deployed, and have a wide range of siting capabilities, it is customary to "saturate" a geographical area with the samplers to assess the air quality in areas where high concentrations of pollutants are possible. Such information is helpful to air pollution control agencies in evaluating their ambient air monitoring networks for consistency with the 40 CFR Part 58 air quality surveillance regulations. In particular, implementing a study using saturation samplers provides data and information to characterize relative pollutant concentrations over the entire saturation study area, locate hot spot or high pollutant impact points, ascertain the need for setting up a reference or equivalent method sampler or monitor, identify an ideal location for establishing a reference or equivalent method sampler site, and evaluate the need to relocate an existing reference or equivalent method sampler.

The EPA established the SMR in 1993 to make saturation samplers more widely available to State, local, and tribal agencies. The SMR includes a pool of 115 saturation samplers and support equipment which agencies may borrow in order to conduct special field studies. The SMR provides limited services to quality assure the samplers and may assist in field studies upon request.

State, local, and tribal agencies have measured concentrations of particulate matter that exceed the PM10 and/or PM2.5 NAAQS. In order to understand the nature of the particulate matter responsible for the exceedance, EPA has provided, as part of the SMR support, filter analysis assistance to requesting agencies operating particulate matter networks.

SATURATION MONITOR REPOSITORY

Eligibility
The SMR provides equipment and other support services to eligible agencies wishing to conduct saturation studies. Generally, the following agencies or organizations are eligible to use SMR resources: EPA's Office of Research and Development (ORD); EPA's Office of Air Quality Planning and Standards (OAQPS); EPA Regional Offices; State, local, and tribal air pollution control agencies; and non-profit environmental research groups under contract to EPA. Requests for services from any of these agencies or organizations are considered on a case-by-case basis by the SMR project officer. The SMR project officer approves requests based on the following criteria: the amount and type of assistance requested, available resources, the general applicability of the study results to other areas, and the date the request is submitted.

Requests for Services
Requests for services must be in writing and be directed to the SMR project officer:
Mr. Neil Berg
U.S. Environmental Protection Agency (MD-14)
Monitoring and Quality Assurance Group
Research Triangle Park, NC 27711
Telephone: (919) 541-5520
e-mail: berg.neil@epamail.epa.gov

A request must include the following items:

  • purpose of the study, including pollutant(s) of interest and benefits of the study
  • location of the study
  • start date and duration of the study
  • number of monitors needed, who will be operating them, and who will be responsible for them other study needs including filters, assistance with planning/site selection/training, etc. when and where the monitors are to be shipped and when they will be returned.

    SMR and Client Responsibilities and Obligations

    The SMR is only responsible for the integrity of the study performed to the extent that the SMR participated in the planning and development of the elements which affect study integrity (e.g., study design, site selection, monitor placement, data handling). Generally, the SMR will not perform any monitoring-related services (unrelated to a specific study), such as upgrading monitors owned by other agencies.

    The client is responsible for ensuring that the equipment borrowed is properly used and sited in such a way as to minimize, as much as reasonably possible, any damage that might occur due to improper use or vandalism. If any damage occurs to the equipment due to negligence or vandalism that could have been prevented, the client is requested to repair or replace the equipment. The client must return all equipment in the same condition as it was received with the understanding that some parts or whole pieces of equipment may need to be replaced during the study period. The client is requested to share data obtained from the study including raw data (upon request).

    SMR Equipment and Services

    Upon approval from EPA's SMR project officer, the SMR will provide any or all of the following equipment and services related to setting up and operating saturation monitoring field studies.

    Saturation Monitors and Sampling Accessories

    The SMR currently includes a total of 115 (98 particulate matter and 17 CO) samplers, which can be used to collect ambient air samples for TSP, PM10, PM2.5, CO, and NOx. With the appropriate filter and analysis technique, lead can also be monitored.

    The SMR also maintains spare parts for the samplers including circuit boards, transformers, diaphragm pumps, impactor jets, hoist poles, valve driver boards, battery packs, rotameters, spare inlet/filter holders, and a supply of the most commonly used filters.

    Equipment Preparation and Shipping

    Once a project has been approved, the saturation monitors are removed from storage and given a performance checkout. The batteries are inspected and charged, flow rates are checked and, if necessary, recalibrated, the inlet/filter holder is examined, and quality control (QC) tests are run as necessary to ensure proper field startup. The monitors are then packed and shipped to the sampling location or to the requesting agency.

    Equipment Return

    Monitors returned to the SMR upon project completion are also subject to check-in procedures before being placed in storage or shipped to another location for additional field use. As samplers are returned to the SMR, the samplers and battery packs are inspected for any visible physical damage, for battery capacity, and for other checks considered necessary to ensure proper operation. If necessary, samplers or battery packs are upgraded according to standard operating procedures (SOPs) before being placed in storage. Appropriate identification tags are placed on equipment to properly identify it as in field ready condition.

    Filter Analysis

    If required and funds are available, the repository can provide filters and filter pre- and post-weighings for gravimetric analysis. Analysis of filters for species composition and particulate properties can also be done on a limited basis, including the following types of analyses:

  • Determination of optical and physical properties such as size, shape, color, texture, transparency and crystallinity through optical microscopy or scanning electron microscopy (SEM)
  • Elemental analysis using methods such as x-ray fluorescence (XRF), neutron activation analysis (NAA), proton induced x-ray emission (PIXE), inductively coupled plasma (ICP) spectroscopy, and atomic absorption spectroscopy (AAS)
  • Analysis of ions such as sulfate, nitrate, and chloride using ion chromatography and ammonium using automated colorimetry
  • Carbon analysis including elemental and organic carbon using temperature controlled combustion techniques and thermo-optical reflectance (TOR)

    Site Selection/Study Design/Training

    Repository personnel are available (travel resources permitting) to assist local agencies in study design and site selection. The SMR can also provide operator training, SOPs, and quality assurance (QA) procedures related to the monitors. In addition, training videos are available that briefly describe the saturation monitor and demonstrate field set up of the sampler and pre- and post-weighing of the filters. These videos are available for use by requesting agencies to supplement SOPs and/or on-site training.

    Quality Assurance

    Standard QA operating procedures are followed during filter weighings and species analysis if applicable. Field audits on the monitors may be performed if requested and travel resources are available.

    Reports

    The SMR will provide to the agency involved a written report of any analyses or other activities performed by the repository. The agency involved will be responsible for validating any data against the original field data forms.

    MINIVOL PORTABLE AIR SAMPLER

    The saturation samplers available through the SMR are manufactured by AirMetrics.1 The AirMetrics portable MiniVol air sampler can be used to collect ambient air samples for TSP, PM10, PM2.5, CO, and NOx. The sampler is compact, lightweight, battery-operated and constructed from durable PVC. The AirMetrics particulate saturation monitor consists of four basic components: a size selective inlet, a combined vacuum source and flow control/flow totalizer unit, a timer, and a portable power source. A diagram of the flow system is shown in Figure 1. It can be operated from either AC or DC power supplies. In operation, the twin cylinder vacuum pump pulls sample air at approximately 5 liters per minute through an impactor which is designed for a cutpoint of either 10 or 2.5 micrometers aerodynamic diameter to remove particles larger than a given size. The sampled air with entrained particulate matter is then drawn through a 47 mm diameter filter where the deposited particulate matter is later measured gravimetrically. The correct particle size collection is obtained by maintaining an actual flow rate of 5 liters per minute at ambient sampling conditions. The sampler power is obtained by use of removable battery packs containing a 12 volt, 8 amp-hour or 12 amp-hour (preferred) sealed lead acid battery and a stepped output charger circuit. The sampler continuously records the battery voltage and air flow rate, automatically shutting off the sampler if limits are exceeded. A programmable timer which can turn power on and off up to six times per day is used to turn the pump on at the desired sample start time and off at the desired sample end time. At the end of each sampling run the sampler must be programmed for the next sample run. The elapsed time indicator is a non-resettable totalizer which is activated when the timer is in the sampling mode. Time is recorded in hours and hundredths of an hour. Figure 2 shows the sampler and support apparatus. Figure 3 shows the PM10 preseparator and filter holder. Figure 4 shows the battery/sampler connection points, and Figure 5 shows the integrated gas sampling arrangement.

    SUMMARY OF SMR ACTIVITIES

    Since the inception of the SMR in 1993, a total of 65 studies have been completed. The number of studies completed each year has increased from two studies in 1993 to 20 studies in 1997. A summary of completed studies is presented in Table 1. Currently, SMR equipment is being used in studies in Hong Kong, Bangladesh, Puerto Rico, and various Regions throughout the United States. The Bangladesh study is looking at multimedia lead contaminants and associated human exposure in the city of Dahka. Puerto Rico is using SMR samplers to assess the PM2.5 problem in various areas around the island. A summary of ongoing studies is presented in Table 2.

    The trend in studies since the inception of the SMR in 1993 is towards larger studies using more samplers. With the July 1997 promulgation of PM2.5 NAAQS,2 SMR activity will likely increase as agencies seek assistance in designing PM2.5 networks and assessing PM2.5 concentrations. One ongoing study involves comparing PM2.5 saturation samplers with prototype PM2.5 federal reference method (FRM) samplers. Specifically, two different configurations of the sampler have been compared with one another and with PM2.5 FRM samplers at a Southeastern site at near optimum conditions. The subject samplers will then be compared to FRM samplers at a Southwestern site that is subject to windblown dust in order to test the sampler's performance using the new tandem 10/2.5 impactors. Samplers with the new configuration will also be compared with PM2.5 FRM and FEM samplers at a site in Southern California during a period when nitrate concentrations would be expected to be high in order to assess whether losses of volatile nitrates in the saturation sampler would be comparable to those from the FRMs.

    FIELD EXPERIENCE WITH THE SMR

    MiniVol Portable Sampler Performance
    Overall, the performance of the SMR saturation samplers in studies has been successful regardless of operator ambient air monitoring experience. For example, operators in one study3 were college undergraduate and graduate students having little or no air monitoring experience. After overcoming initial startup data capture problems, the overall data completeness was 70 percent. Other studies have reported higher data capture. However, data capture problems have been reported in a number of studies. These problems can be broken down into four categories: (1) operator error, (2) battery problems, (3) sampler component failure, and (4) extreme environmental conditions. Typical problems in these categories are highlighted below:

    1) Operator Error: Improper low flow zero and cutoff adjustments can cause the sampler to shut off when the flow rate drops only slightly. The manufacturer's procedures for "Low Flow Zero and Cutoff Adjustments"1 should be followed to correct this problem. Improper timer settings are also relatively easy to check and fix. Missetting day/time, having additional, unwanted programs still in the programmable timer, and failing to set the timer back to auto can also result in short sampling times.

    2) Battery Problems: Older 12-volt, 8 amp-hour batteries may not be adequate for 24-hour sampling under conditions of high particulate loading. Upgrading batteries to newer 12-volt, 12 amp-hour batteries according to manufacturer's procedures1 may resolve some battery problems. Batteries should also be tested to ensure that they will hold a charge and will not drain too quickly; fully charged batteries will usually register above 13 volts. Note that problems may also exist with the battery charger or the charging circuitry in the battery portion of the sampler as described below.

    3) Sampler Component Failure: Bad connections between the battery and the pump can occur in several places - where the sampler unit pins fit into the battery unit sockets, leads from the battery to the battery circuit board, leads from the sockets to the to the sampler circuit board, and solder joints and connections along the way, including on the circuit boards. These problems can usually be identified through careful visual inspection and use of a multimeter. As sampling time accumulates or under hard use or abuse, major components (e.g., the pump, programmable timer, or main circuit board) may fail and need to be replaced.

    4) Extreme Environmental Conditions: Problems with the sampler may be caused by extreme cold or heat, excessive moisture or windblown precipitation, excessive vibration (for example, at sites located over or close to subway train routes), and electrical interference (for example, traffic light control signals, mobile phone signals, CB radios, and air traffic control signals). Problems with excessive cold can be addressed by using supplemental heaters around the unit (such as a small light bulb in an insulating blanket); problems with extreme heat have not been reported to the SMR but can occur; problems with excessive vibration and electrical interference have been suspected but not clearly demonstrated.

    High particulate loadings may also result in sampler problems by causing excessive pressure drop across the filter leading to excessive pump drain on the battery and premature sample cutoff due to low flow. With generally high particulate concentrations (frequently above 200 g/m3), the PM10 and PM2.5 inlets should be cleaned and the impactor plate(s) greased more frequently than normal. AirMetrics' revised designs for PM10 and PM2.5 inlet/impactors may help to reduce problems with particle bounce in dusty conditions. Use of a special higher capacity battery unit, a non-battery power source, or more than one sampler for a given 24-hour sampling period (e.g., two samplers set for 12 hours each in sequence) may be necessary to resolve overloading problems.

    Comparison of PM10 and PM2.5 Results

    While most saturation sampling has historically been for PM10, saturation sampling for PM2.5 has increased in recent years in anticipation of the recently promulgated PM2.5 standard. Prior to promulgation of the PM2.5 NAAQS, there were no PM2.5 reference or equivalent methods and therefore no definitive "standard" samplers against which to compare the results of the PM2.5 saturation sampler. Results of comparisons of the PM2.5 saturation sampler with other PM2.5 samplers have been mixed. For example, the PM2.5/PM10 ratio obtained using saturation samplers for a 1994 Philadelphia study4,5 (0.76) was in excellent agreement with the ratio obtained at many of the same sites in an earlier study by Harvard (0.75) using samplers with a PM2.5 size cut cyclone. On the other hand, a 1996 Manhattan study3 found that while the PM10 saturation samplers gave results that were in excellent agreement with PM10 equivalent method dichotomous samplers, the PM2.5 samplers gave results that were more than 28 percent higher than the PM2.5 fraction measured by the dichotomous samplers.

    AirMetrics has recently redesigned its PM2.5 size fractionator in order to improve performance under dry, windblown dust conditions. The revised impaction plate is slightly bowl-shaped instead of flat as in the old configuration. The revised PM2.5 size fractionator now consists of two impactors in series, a PM10 impactor followed by a PM2.5 impactor. The revised design is shown in Figure 6.

    In a recent study,6 two sets of PM2.5 saturation samplers (one set with the old single-stage flat plate impactor and the other set with the new tandem 10/2.5 impactors with bowl-shaped impactor plates) were compared, under "best case conditions," to each other and to a series of prototype PM2.5 FRM samplers. Relative accuracy and pooled precision were about 10 percent and 4 percent, respectively, for the old sampler configuration and 2 percent and 7 percent for the new configuration. Precision was about 2 percent for the FRMs. The results of the initial stage of the study indicate that, under good conditions, the saturation sampler using the old configuration likely overestimated PM2.5 concentrations by about 10 percent compared to concentrations that would have been obtained using a FRM sampler. The saturation sampler with the new configuration is likely to measure PM2.5 concentrations that agree, within its measurement precision, with those taken by an FRM.

    CONCLUSIONS

    The EPA established the SMR in 1993 to encourage the conduct of short-term, multi-site ambient air pollutant monitoring studies for the major purpose of evaluating the consistency of existing ambient air monitoring networks with the 40 CFR Part 58 air quality surveillance regulations. The program has been highly successful with a total of 65 studies completed since the inception of the program. After initial start up problems have been resolved, the samplers have proven to be easy and relatively inexpensive to operate and capable of providing good data capture. Separate study results have shown the PM10 saturation samplers provide good comparisons with PM10 equivalent method dichotomous samplers while the initial PM2.5 saturation samplers gave results that were more than 28 percent higher that the PM2.5 fraction of the dichotomous samplers. PM2.5 saturation samplers with the older PM2.5 inlet/impactor gave results that were approximately 10 percent higher than prototype FRMs. Redesigned PM2.5 saturation sampler fractionators have shown significant improvement with the saturation sampler measuring PM2.5 concentrations that agree with those measured using prototype PM2.5 FRMs. Because of the need for control agencies to establish PM2.5 FRM networks, the demand for special studies using the new PM2.5 saturation samplers is expected to increase significantly.

    REFERENCES

    1. AirMetrics, MiniVol Portable Sampler Operation Manual, Springfield, OR, June 1993.
    2. "Revised Requirements for Designation of Reference and Equivalent Methods for PM2.5 and Ambient Air Quality Surveillance for Particulate Matter; Final Rule," Federal Register, Vol. 62, No. 138, July 18, 1997.
    3. TRC Environmental Corporation. "Manhattan Community Based Particulate Study Final Report;" TRC Document No. CH-97-02, Prepared for U.S. EPA Region II Air Programs Branch, January 1997.
    4. Tropp, R.J.; Sleva, S.F.; Ramadan, W.; Harris, C.J.; Berg, N.J. "Results of the 1994 Philadelphia PM2.5 and PM10 Saturation Study," Presented at the 89th Meeting of the Air & Waste Management Association, Nashville, TN, June 1996; paper 96-MP3.03.
    5. TRC Environmental Corporation. "1994 Philadelphia PM2.5 and PM10 Saturation Study Revised Final Report;" TRC Document No. CH-95-105, Prepared for U.S. EPA Monitoring and Quality Assurance Group, November 1995.
    6. Tropp, R.J.; Jones, K.; Kuhn, G.; Berg, N.J. "Comparison of PM2.5 Saturation Samplers with Prototype PM2.5 Federal Reference Method Samplers;" Presented at the Air & Waste Management Association Specialty Conference on PM2.5: A Fine Particle Standard, Long Beach, CA, January 1998.

    TABLE 1. SMR Studies Completed During the Period September 1995 through January 1998.
    Agency Request Study Purpose Study Duration Pre- and Post-Filter Weighing
    California Air Resources Board 6 PM To determine PM2.5/PM10 ratios. Jan - May 1996 No
    Maricopa County 15 PM10 To determine PM10 levels at selected sites. 1995 - Jan 1996 No
    NCDEHNR 11 PM To determine PM emissions from a cotton mote facility. Jan - Apr 1996 No
    City of Philadelphia 9 PM2.5 To determine PM2.5 levels at selected urban area sites. Mar - Jul 1996 Yes
    Pike's Peak Area Council of Govts. 8 PM To determine PM10 air monitoring levels. Jan - Aug 1996 No
    EPA Region II 45 PM To study PM2.5 values in upper Manhattan. Jul - Oct 1996 Yes
    EPA Region III 4 PM2.5 To determine PM2.5 levels at selected expected high concentration urban area sites. Oct - Dec 1996 Yes
    ENSR 10 CO To provide better dispersion modeling information for use in the vicinity of petroleum refineries. Oct - Dec 1996 No
    NCDEHNR 12 PM To determine PM levels from burning of Hurricane Fran debris. Oct - Dec 1996 No
    NCDEHNR 11 PM10 /PM2.5 To determine PM10 and PM2.5 levels at selected sites. 1996 - Jan 1997 No
    Region VIII 3 PM2.5 To compare PM2.5 samplers with proposed FRM. Nov 1996 - Jan 1997 No
    EPA MQAG 6 PM2.5 To compare PM2.5 samplers with proposed FRM. Apr - May 1997 Yes
    Municipal Environmental Commission 1 CO, 1 PM2.5 To determine PM and CO outflow from the Holland Tunnel. Feb 1996 - Sep 1997 No
    EPA Region II 16 PM To determine PM concentrations in Queens, NY Jun 1997- Jan 1998 No
    Ventura County APCD 10 PM2.5 To study PM2.5 values within Ventura County and to establish baseline values at the current air monitoring stations to facilitate development of the Ventura County PM-fine monitoring plan. May 1996 - Apr 1997 Yes
    Cincinnati 1 PM2.5 To determine PM concentrations around burning landfill followed by periodic sampling at selected sites. Jul 1996 - May 1997 No
    EPA Region VIII 5 PM2.5 To better characterize PM emissions in Montana's tribal nonattainment areas to allow EPA to better target control strategies. Nov 1996 - Dec 1997 No

    TABLE 2. SMR Studies Ongoing as of February 1998.
    Agency Request Study Purpose Study Duration Pre- and Post-Filter Weighing
    EPA ORD 10 CO/PM10 To determine PM levels at selected urban area sites in Hong Kong Sept 1997 - 1998 No
    NCDEHNR 2 PM2.5 To determine the impact of suspended PM sources near residences located at valley exit. May 1996 - Jun 1998 No
    EPA Region VII 5 PM2.5 To determine PM levels in urbanized areas. Mar 1996 - 1998 No
    USDA Agricultural Center 15 PM To determine the relationship between PM10 readings and soil erosion by wind. Feb 1994 - 1998 No
    Puerto Rico EQB 15 PM To determine PM10 and PM2.5 in selected areas around the island. Dec 1997 - Sept 1998 Yes
    Washington State University 10 PM To determine PM emissions from windblown dust at three different elevations at a site near Spokane, Washington. Feb 1994 - Dec 1998 No
    Missouri DNR 6 PM2.5 To determine PM levels at selected sites in Missouri. Nov 1996 - 1998 No
    WIDNR 4 PM2.5 To determine PM levels at selected urban area sites. Nov 1996 - 1998 No
    City of Indianapolis 8 PM2.5 To determine PM levels at selected urban area sites. Nov 1996 - 1998 No
    University of Texas at Austin 2 PM To determine the lead content in ambient air. Sept 1997 - Jun 1998 No

     

    Figure 1. Block diagram of saturation monitor flow system.

    Figure 2. Mounted saturation sampler.

    Figure 3. PM10 preseparator and filter holder.

    Figure 4. Battery/sampler connection points.

    Figure 5. Integrated gas sampling arrangement.


    Figure 6. Revised PM2.5 preseparator and filter holder.