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FHWA and EPA National Near-Road Study - Detroit

5 Analytical Instruments and Methods

5.1 Data Logging and Time Synchronization

All continuous analyzer data were recorded using an Ecotech 9400TP data logger. These loggers were programmed to record continuous data (averages) at 5-minute intervals. Moreover, these data loggers were time synchronized to National Institute of Standards and Technology (NIST) time by accessing the NIST internet web site hourly and adjusting the data loggers' internal time clock accordingly.

5.2 WinAQMS and WinCollect Software

Ecotech WinAQMS server software was loaded onto the data loggers to handle communications between the continuous analyzers and the data loggers¹⁷. Ecotech WinCollect software was loaded onto a Windows XP workstation at the EPA Facility in RTP, NC to monitor and determine instrument status and performance, perform remote calibrations, determine data validity and download data from the remote field site to the Near-Road database¹⁸. This data was loaded into a SAS database for further quality assurance (QA) and data analysis.

5.3 Traffic Activity

EPA assumed a more active role in Detroit due to lessons learned in Las Vegas. Moreover, EPA utilized next generation radar devices; one looking at east bound traffic, a second device looking at west bound traffic along I-96. EPA installed a Wavetronix SmartSensorHD unit at the 10 meter roadside site; the second unit was located on the upwind side (south) of the freeway. Each unit pointed across the freeway and data was collected and stored onto an EPA computer.

Historically, traffic data is reported as an annual average daily traffic (AADT). Historically, these values are not measured 24-7, 365 days per year. Traffic data is collected for 1-2 weeks during the year for a highway segment; monthly and seasonal factors are applied to calculate AADT. The importance of this historical information relative to our project is that the project has highly time-resolved data for analysis of roadside concentration measurements.

Figure 16 shows average hourly traffic speed and volume at the I-96 site.

Figure 16. Hourly Average Traffic Volume and Average Speed -- I-96.

5.4 Meteorology

Meteorological monitoring characterized ambient conditions during the day and included measurements for: wind speed, wind direction, ambient temperature, relative humidity, solar radiation, and precipitation. Wind speed and wind direction were characterized by sonic anemometers (R.M. Young Model 81000 Ultrasonic Anemometers). Temperature and relative humidity were characterized by Vaisala HMP45D and Vaisala HMP45A probes, respectively. Barometric pressure was measured by Vaisala PTB210 probe. Solar radiation was measured by a MetOne 394 Pyranometer and precipitation was measured by a rain bucket (Ecotech Rainmaster 1000).

5.5 Continuous Analyzers

5.5.1 Gaseous Pollutants

Gas analyzers (Table 1, Table 8) meeting U.S. Environmental Protection Agency Federal Reference Method (FRM) or equivalent method criteria collected measurements of CO, NO, NO₂, NO_X, at 100 meters upwind, 10 meter roadside, 100 meters downwind and 300 meters downwind from the freeway. The sample height in all cases was at approximately 3 meters above the ground. Data was logged continuously for 5-minute averaging periods over the course of the study period (Table 9). Multi-point calibrations occurred at the beginning of the study while zero and span checks were run every night over the course of the study period.

5.5.2 Black Carbon

Black carbon (BC) was measured continuously at each station using dual-wavelength rackmount Aethalometers (Table 1, Table 8) at 100 meters upwind, 10 Meter Roadside, 100 meters downwind and 300 meters downwind from the freeway. The sample height in all cases was at approximately 3 meters above the ground. Data was logged continuously for 5-minute averaging periods over the course of the study period (Table 9).

The Aethalometer continuously measures BC at five minute intervals by pulling air through a small spot on the sample filter and detecting incremental changes in light attenuation at a specific wavelength. Once the sample spot is loaded to a certain limit, the instrument automatically pauses, rotates the filter tape through to a new clean spot, and begins sampling again; this translates to a ten minute gap in the data approximately twice per day in the Detroit data set. The main wavelength of light used to detect BC is 880 nm, in the red region of the visible spectrum. In addition, this instrument also detects light attenuation at 370 nm and is a qualitative indicator of additional particulate organics which may absorb light at near-ultraviolet wavelengths.

Black carbon values are calculated by the below equation,

BC = ∆ATN *A/ SG* Q*∆t (1)

where, BC is the concentration of black carbon in the sample (units of ng/m^-3), ∆ATN is the change in optical attenuation due to light absorbing particles accumulating on a filter, A is the spot area of filter, Q is the flow rate of air through filter, ∆t is the change in time, SG is specific attenuation cross-section for the aerosol black carbon deposit on this filter (16.6 m²/g). SG is an empirical value that was defined by the manufacturer as the ratio of the mass of elemental carbon (measured using a thermal-optical process) and the detected light absorption of the same sample on a filter.

BC data was automatically logged by two methods during the Detroit monitoring period - logging its full set of data fields (17 columns of data) at five minute intervals to a text file using Hyper Terminal and directly logging only the BC concentration estimated from the instrument's analog output to the station database. The analog data was used during the course of the monitoring study to observe the instrument's performance, however the digital data logged to the text file was used as the primary data for analysis, per manufacturer's recommendations.

Further details are in Appendix 13.

5.5.3 Particulate

Particulate analyzers (Table 1, Table 8) meeting U.S. Environmental Protection Agency Federal Reference Method (FRM) or equivalent method criteria collected measurements of PM-Coarse (particles that have an aerodynamic diameter ranging from 2.5 to 10µm) , PM₁₀ and PM_2.5, at 100 meters upwind, 10 meter roadside, 100 meters downwind and 300 meters downwind from the freeway. Aethalometers and continuous particle counters (Table 1and Table 8) measured black carbon and particle counts at 100 meters upwind, 10 meter roadside, 100 meters downwind and 300 meters downwind from the freeway. The sample height was at approximately 3 meters above the ground. Data was logged continuously for 5-minute averaging periods over the course of the study period (Table 9).

Continuous PM-Coarse, PM₁₀ and PM_2.5 measurements were collected by four Thermo Electron Tapered Element Oscillating Microbalances (TEOM) Model 1405-DF at a flow rate of 16.7 liters/minute (L/min) (1.0 m3/hour). The data were recorded as 5-minute averages (Table 9).

5.5.4 Integrated Samples - VOC, Carbonyl, Particulate

Specific MSATs of interest for this study included: 1,3-butadiene, benzene, acrolein, formaldehyde and acetaldehyde. MSAT samples were collected using U.S. Environmental Protection Agency standard methods: 1) TO-15 and 2) TO-11A. The integrated sampling schedule implemented in Detroit was significantly modified from the Monitoring Protocol. The integrated sampling campaign in Detroit focused on peak periods of traffic (commute times). The figures on the next page show average hourly traffic volumes. These hourly volumes show peak commute times for both east bound and west traffic on I-96 in the vicinity of Eliza Howell Park. From these peak commute times sample times were selected for the MSAT sampling (7 - 8 am and 5 - 6 pm). Samples were collected on a quarterly basis with 5 sample days during the quarter and 2 samples being collected at each station on each sample day during the sample period. This sample strategy followed the 1-in-3 day ambient air quality monitoring schedule that corresponded to the schedule posted on EPA's web site¹⁹ and followed by State/local air agencies for ambient air quality monitoring. The EPA PM_2.5 federal reference method (FRM) was used for the collection of PM_2.5 integrated samples.

Quarterly basis was defined as four 3-month periods. The sample periods overlapped from one quarter to the next quarter. The sample periods were scheduled to minimize operating costs and maximize sample distribution across quarters with respect to seasonal data collection. Moreover, blanks and duplicates will be incorporated into the sampling regime.

I-96 East Bound at Telegraph Road

I-96 West Bound at Telegraph Road

The following calendar shows this sampling scheme. Days shown in bold text are sampling days corresponding to 1-in-3 sampling schedule.

5.5.4.1 EPA Compendium Method TO-15 - Canister - VOC

Collection of canister samples by the TO-15 method calls for the atmosphere to be sampled by the introduction of air into a specially-prepared stainless steel canister. An Entech Model 1816 programmable multi-canister automated sampler was used to accurately regulate the filling of the sample canisters with air. Evacuated SUMMA passivated 6 liter (L) canisters were filled to near ambient pressure. A nominal flow rate of 75 milliliter/minute (mL/min) was maintained over a 1-h sampling period for a total sampled volume of approximately 4.5 L. Evacuated canisters received from the laboratory and ready for sampling were placed on the Entech sampling system by attaching each canister's valve to individual sampling ports. The initial pressure was measured for each canister to insure that every canister falls within an acceptable pressure range (<0.5 psia). Any canisters above the acceptable range were replaced with one that met the initial pressure criteria (0.5 psia). With the canisters attached, each port was leak checked to insure that fittings had been properly tightened and the samples would not leak prior to and after collection. Sample labels printed with the individual sample codes were affixed to the canister tags for sample identification. The sampler was programmed for the scheduled sampling times and flow rates. Timers and solenoids within the Entech sampler were activated and deactivated allowing sample collection based on the entered sampling program. After the air samples were collected, the canister valves were closed and the canister prepared for shipment to the laboratory for analysis. Sample collection information such as initial and final pressures, initial and final times, canister id number, etc. were either hand recorded on a data collection form for subsequent entry in the electronic data form or entered directly into the electronic data form. Chain-of-custody (COC) sheets were generated and the samples were shipped to the laboratory. Upon receipt at the laboratory, the canister sample label was compared against the datasheet and the COC sheet. Any discrepancies were resolved at that time. The samples were stored until the laboratory analysis of the canisters was completed.

5.5.4.2 EPA Compendium Method TO-11A - Cartridges - Carbonyl

The EPA Compendium TO-11A DNPH carbonyl method was implemented in Detroit for the collection and analysis of air samples for formaldehyde and acetaldehyde. DNPH sampling cartridges are commercially available for this method and were purchased and provided for field sampling. Air samples for carbonyls on DNPH cartridges were collected using an ATEC 8010 automated sampler manufactured by Atmospheric Technology (ATEC). This was the same instrument used for the DNSH cartridge sampling. The instrument is a microprocessor controlled sampler that can be programmed to draw ambient air at a constant rate through various types of sampling cartridges for designated time periods. The sampler consists of two units (channels) each having 10 active sampling ports and one non-active port. Channel 1 (ports 1-10) was used for the DNPH samplers and Channel 2 (ports 11- 20) was used for the DNSH samplers. DNPH samples were collected at a flow rate of 1.00 lpm for a one hour time period.

DNPH cartridges were attached to the ATEC's Teflon sampling lines and labeled with the sample collection code. A leak check of each cartridge was performed using the leak check feature of the Atec sampler. This ensured that the cartridges were installed properly. A light blocking sleeve was installed around each cartridge to reduce artifacts due to light sensitivity. The sampler was programmed with the flow, start time and end time for each cartridge channel. During sampling, solenoid valves associated with each cartridge was activated/deactivated based on the programmed sampling schedule. Upon completion of sampling, the cartridges were removed, capped, secured for shipment, and returned via overnight delivery to the EPA RTP facility. Sample collection information such as initial and final flow rates, initial and final times, and canister id number, were either hand recorded on a data collection form for subsequent entry in the electronic data form or entered directly into the electronic data form. COC sheets were generated and the samples shipped to the laboratory. While awaiting shipping, samples were stored in an on-site refrigerator. A cooler with frozen blue ice packs was used to ship the cartridges.

5.5.4.3 Particulate

A BGI PQ 200A PM_2.5 federal reference method (FRM) sampler was used for the collection of PM_2.5 integrated samples. Cassettes loaded with pre-weighed 46.2 mm Teflon filters were prepared at the EPA RTP facility by EPA staff and shipped to the Detroit field staff. Filter IDs were linked to unique sample codes generated and printed by data collection spreadsheets. Samples were collected over a 24-h period beginning at midnight of the sampling day. Flow rates and pressures were recorded by the sampler. At completion, the filter was removed and flow rates and pressures were transcribed onto the data collection spreadsheets. The filter cassettes were removed, packed for shipment, and returned by overnight delivery to EPA RTP.

Table 8. Summary of Measurement Parameters, Sampling Approach, Instruments, and DQI Goals for Project.

2. Accuracy and precision in terms of ultrafine particle concentration is difficult to determine in the field due the lack of particle concentration standards. However, particle counters are routinely verified in the field for accuracy in flow rate. Precision was estimated in this study by collocating UFP samplers prior to use of instruments in the field.

Table 9. Summary of Detroit Data Types, Pollutants, Methods and Sample Types and Frequency.