Construction of a DOAS Instrument for Installation at CARB
Understanding the nature of the sulfur and sulfate in combustion and lubricant-derived particles is important to characterize to better understand the relative contribution of fuel vs. oil sulfur, to understand storage vs release of sulfur from catalyzed surfaces, and measure the sulfur fraction partitioning into the PM nucleation particles. The objective of this research is to construct, test and provide to ARB laboratories a differential optical absorption spectrometer (DOAS) that can measure down to 20 ppbV in real time and determine a mass balance between SO2 and sulfate. The DOAS developed under this program was evaluated using a series of laboratory performance tests at the CE-CERT laboratory. The DOAS will be installed and operated in the ARB Heavy Duty Emissions Test Laboratory. The differential optical absorption spectrometer (DOAS) developed for this project was specially designed and built for rapid, extractive detection of sulfur dioxide at low ppb levels for the ARB. The integrated system consists of the extractive sampling train, the sampling cell, and the spectrometer. The sample cell uses a single-path design with beam expanding and focusing optics to minimize cell volume. The sample cell for the UC Riverside system is cylindrical with a length of 1.0 m and a total volume of approximately 0.51 liters. To avoid possible interferences from other exhaust constituents, the spectral range was restricted to the UVB region (200–230 nanometer (nm)). The DOAS software also allows for additional subsections of the spectral range to be selected to minimize interferences from species such as NH3. A deuterium lamp was used as the light source. The cell is designed to operate over a full 8-10 hour testing day at a temperature of 110°C, with a temperature range from 25°C up to 120°C (250oF). Laboratory tests were conducted to evaluate the response of the SO2 monitor to a range of operating conditions, from ambient conditions to those most representative of exhaust gas emanating from vehicles. These laboratory tests showed detection limits were approximately in the range of 12 to 15 ppbV. The instrument showed good linearity over SO2 concentration ranges of 20 to 953 ppbV. A number of interference tests were conducted, focusing on potential interferences between SO2, NO, and NH3. Initial tests showed some interference with either NO or NH3, at levels of 80 ppbV and 680 ppbV. Initial tests at 300 ppmV of NO and 16.6 ppmV of NH3 confirmed that at these high levels they would interfere with the SO2 response over the spectral range specified. With a modification of the spectral range to 206 to 214 nm, the DOAS interference SO2 response was less than 1.5 ppbV with 300 ppmV of NO injected with, and was slight less than 8 ppbV with 16.6 ppmV of NH3 injected. The DOAS was evaluated over vehicle emissions tests in CE-CERT’s light-duty chassis dynamometer laboratory. The results showed no appreciable SO2 interferences for the tests on the diesel truck, which had very low NH3 emissions. Clearly, in a low NH3 environment, as tested here the SO2 detection is unbiased and meets the laboratory tested detection limits of around 20 ppbV. If the DOAS is used in a low NH3 environment, as in this test, it should achieve the expected detection limits. The gasoline vehicles, on the other, had higher levels of NH3, and showed a significant interference, especially when the NH3 values exceeded 11 ppmV. If it is to be used for vehicles with higher levels of NH3, an NH3 scrubber would likely be needed to scrub the level of NH3 in the exhaust to no greater than 10 ppmV, as well as perhaps some additional updates to the software that are currently being developed. If an ammonia scrubber is used, it is recommended that SO2 measurements be made both with and without the scrubber in order to determine whether there is any appreciable effect on the measurements. vi Development and Installation of an SO2 DOAS Acronyms and Abbreviations ARB ...................................................Air Resources Board CARB .................................................California Air Resources Board CE-CERT ...........................................College of Engineering-Center for Environmental Research and Technology (University of California, Riverside) CFO ....................................................critical flow orifice CCD ...................................................charge-coupled device CPU ....................................................central processor unit DECSE ...............................................Diesel Emission Control – Sulfur Effects project DOAS .................................................differential optical absorption spectroscopy DPF ....................................................diesel particulate filter mm .....................................................millimeter NIST ...................................................National Institute of Standards and Technology nm ......................................................nanometer NOx ....................................................nitrogen oxides PM ......................................................Particulate matter SCR ....................................................selective catalytic reduction SO2 .....................................................sulfur dioxide SSR ....................................................solid-state relays UCR ...................................................University of California at Riverside UV ......................................................ultraviolet vii Development and Installation of an SO2 DOAS Executive Summary Since sulfur and sulfate are some of the main components of combustion and lubricant-derived particles, it is important to characterize sulfur species and understand the composition and potential health impacts of particles. Sulfate levels in vehicle exhaust particulates can be readily measured, but it is important to understand the relative contribution between combustion and oil-derived particles and the conversion rates found for SO2 to sulfate. With the low level of sulfur present in the fuel and oil products used in modern vehicles, detection limits in the ppb range are needed to measure the SO2 contribution. One technique that has been shown to provide real-time, low-level measurement of engine-out SO2, is differential optical absorption spectroscopy (DOAS). DOAS technology provides the potential for very low detection limits, along with the capability of measuring SO2 in real-time. Over the past decade, there have been numerous advances in DOAS technology that have allowed for the development of instruments with lower detection limits in conjunction with smaller sample cells to provide improved residence times. The objective of this study was to construct, test, and provide the ARB with a state-of-the-art DOAS that can measure SO2 down to 20 ppbV in real-time. The DOAS developed under this program was evaluated using a series of laboratory performance tests at the CE-CERT laboratory. The DOAS will be installed and operated in the ARB Heavy Duty Emissions Test Laboratory. The major conclusions from the findings are summarized in the following:  The differential optical absorption spectrometer (DOAS) developed for this project was specially designed and built for rapid, extractive detection of sulfur dioxide at low ppb levels for the ARB. The integrated system consists of the extractive sampling train, the sampling cell, and the spectrometer.  The sample cell uses a single-path design with beam expanding and focusing optics to minimize cell volume. This allows the highest amount of throughput for a given amount of initial light energy and is essential with a small diameter sample cell. The small diameter was a design parameter to minimize the cell volume which yields reduced residence time of the exhaust gas in the cell. The sample cell was designed as an open cell with the sample cell residing between the windows, rather than having the transmitting and collecting optics inside the sample cell.  The sample cell for this system is cylindrical with a length of 1.0 m. The total volume of the DOAS sample cell is approximately 0.51 liters.  The cell is designed to operate over a full 8-10 hour testing day at a temperature of 110°C, with a temperature range from 25°C up to 120°C (250oF).  To avoid possible interferences from other exhaust constituents, the spectral range was restricted to the UVB region (200–230 nanometer (nm)). For the 200–230 nanometer (nm) region, a deuterium lamp was used as the light source. Additional adjustments were also made to allow for subsection of the spectral range to be selected for analysis, to minimize interferences from species such as NH3, such as narrowing the spectral range to 206 nm to 214 nm.  The spectrometer/receiver consists of a single working element, a concave 1200 groove/millimeter (mm) holographic diffraction grating optimized for 200–230 nm.  The DOAS software, LasIRView 2009, is a user-friendly Windows-based based package with outputs for data logging and a software manual. The DOAS software was upgraded to provide an adjustable window over the spectral range, such that interferences from species such as NH3 can be minimized. viii Development and Installation of an SO2 DOAS  Laboratory tests were conducted to evaluate the response of the SO2 monitor to a range of operating conditions, from ambient conditions to those most representative of exhaust gas emanating from vehicles.  Detection limits were approximately in the range of 12 to 15 ppbV at three times the standard deviation of zero gas response.  The linearity of the instrument was evaluated over SO2 concentration ranges of 20 to 192 ppbV and 51 to 953 ppbV. The regression analysis showed a slope of 1.011 and 0.995, respectively, and R values of 1.0 and 0.999, respectively, for these ranges.  A number of interference tests were conducted, focus
DEACTIVATION OF THREE-WAY CATALYSTS BY FUEL CONTAMINANTS:--LEAD, PHOSPHORUS AND SULFUR
Poisoning of a typical platinum-rhodium (Pt-Rh) automotive three-way catalyst (TWC) was determined as a function of lead (Pb), sulfur (S) and phosphorus (P)fuel levels, thermal aging and sulfur dioxide content in the evaluation fuel. In an attempt to mimic the effect on TWCs of misfueling with Pb levels typical of commercially available leaded fuels, TWC activities were severely poisoned. Upon reverting to fuel containing trace Pb levels, the CO activity was restored, but the NO and HC activities were only partially recovered. The Pt-Rh TWCs were poisoned by the exhaust from fuel containing 0.03 wt % S, but not by that from fuel containing up to 8 mg P/gal (2.1 g/cu m).
Simultaneous NO and CO Conversion over Rhodium
Various catalysts are examined for the simultaneous removal of CO and NO in an exhaust-like feed. Rhodium supported on alumina possesses exceptionally high activity for reducing NO but forms mostly NH3 below 600°C. At higher temperature NH3 is an intermediate in the reduction of NO to N2. CO and H2 are oxidized at comparable rates as the oxygen content of the feed is increased, so NH3 formation is not checked by selective H2 removal below 600°C. On the other hand, above 600°C ammonia removal is enhanced by oxygen.