Environ. Sci. Technol. 2004, 38, 5968-5976
Simultaneous Determination of Carbonyls and NO2 in Exhausts of Heavy-Duty Diesel Trucks and Transit Buses by HPLC following 2,4-Dinitrophenylhydrazine Cartridge Collection S H I D A T A N G , * ,† L I S A G R A H A M , ‡ LING SHEN,§ XIANLIANG ZHOU,§ AND THOMAS LANNI† Bureau of Mobile Sources and Technology Development, Division of Air Resources, New York State Department of Environmental Conservation, Albany, New York 12233, Emissions Research and Measurement Division, Environment Canada, Ottawa, Ontario, Canada K1A 0H3, and Wadsworth Center, New York State Department of Health, Albany, New York 12201
A method combining 2,4-dinitrophenylhydrazine (DNPH) cartridge sampling and high-performance liquid chromatography (HPLC) analysis has been used for the measurement of carbonyl and NO2 emissions from heavy-duty diesel trucks and transit buses. The reaction of NO2 with DNPH allows for the simultaneous and unambiguous determination of NO2 and carbonyl concentrations in exhaust samples. The potential coelution of the NO2-DNPH derivative with the formaldehyde-DNPH derivative under certain chromatographic conditions was investigated. Successful separation of these two species was achieved allowing for simultaneous determination of carbonyls and NO2 in the exhaust samples collected from heavy-duty diesel (HDD) trucks and diesel, diesel/electric hybrid, diesel equipped with the continuously regenerating technology (CRT) particle traps, and compressed natural gas (CNG) transit buses tested over various drive cycles. Elevated NO2 emissions from CRT-equipped buses were observed. The NO2/NOx volume ratios for HDD trucks and transit buses are discussed. A comparison of the DNPH derivatization with HPLC/UVvisible detection method with a chemiluminescence analyzer method for NO2 measurement is presented for a limited number of diesel/CRT and CNG buses.
Introduction The U.S. EPA 1996 National Toxics Inventory (NTI) has estimated that a substantial share of the total national emission of formaldehyde (49%), acetaldehyde (70%), and acrolein (39%) are attributable to mobile sources. These three carbonyl species were among the 21 mobile source air toxic pollutants (MSATs) cited by the U.S. EPA in a March 29, 2001, rulemaking (1). Of the 21 MSATs in the U.S. EPA rule, * Corresponding author phone: (518)782-7248; e-mail: sdtang@ gw.dec.state.ny.us. † New York State Department of Environmental Conservation. ‡ Environment Canada. § New York State Department of Health. 5968
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 38, NO. 22, 2004
only formaldehyde is currently regulated in mobile source tailpipe emissions. The U.S. EPA has set formaldehyde emission standards for heavy-duty spark ignition and compression ignition engines in the Clean-Fuel Fleet program and for passenger cars, light-duty trucks, and medium-duty passenger vehicles in the U.S. EPA Tier 2 emission standards that will be phased in over the 2004-2009 model years (24). Following methodologies originally developed for ambient air sampling, vehicle exhaust carbonyls are commonly collected by derivatization with 2,4-dinitrophenylhydrazine (DNPH) to form hydrazones (DNPHzones) using either a DNPH-coated absorbent or an absorbing solution of acidified DNPH in acetonitrile in a midget impinger (5, 6). The method has been refined by using low-pressure drop DNPH-coated silica cartridges (7), which are much easier to handle than the liquid-filled impingers and are easier to protect from contamination before and after sampling. Determination of DNPHzones is achieved using high-performance liquid chromatography (HPLC) with ultraviolet-visible (UV-Vis) detection at a selected wavelength (7, 8). Aliphatic carbonyls containing up to 6 carbon atoms and the 7-9 carbon aromatic carbonyls are typically identified and quantified with good sensitivity for routine measurements of carbonyl emission rates at or below mg/mi levels. Oxides of nitrogen (NOx) in ambient air (primarily NO and NO2) make significant contributions to urban ambient air pollution (9), playing a critical role in the atmospheric photochemistry that produces ground-level ozone (10). NO2 participates in many other atmospheric reactions, in particular the oxidation of organic compounds leading to potent pollutant species such as peroxyacetylnitrate (PAN). The health-based U.S. federal air quality standard for NO2, measured as an annual arithmetic mean concentration, is 0.053 ppm or 100 µg/m3 (11). The U.S. EPA vehicle emission certification testing procedures specify a chemiluminescence analyzer (CLA) for determining NOx emissions. The CLA measures the photoemission from excited NO2 produced by the reaction between NO and ozone. The required ozone is produced in the instrument by a high-voltage discharge in oxygen. For total NOx measurement, a catalytic converter reduces sample NO2 to NO prior to the ozone reaction chamber, thus allowing the CLA to measure both NO2 and NO as NOx. CLAs can measure NO2 specifically from the difference between the NOx and NO measurements. An alternative method for determining NO2 takes advantage of the reaction of NO2 and DNPH to form 2,4dinitrophenyl azide (12), referred to in this paper as DNPA. As DNPA and DNPHzones absorb at different wavelengths, a separate analysis is required for NO2 and carbonyls analyses when a single wavelength UV-Vis detector is used. Simultaneous measurements of DNPA and DNPHzones derivatives can be achieved by using a photodiode array (PDA) detector. Hamm et al. (13) report that DNPA can coelute with the formaldehyde-DNPH derivative under certain chromatographic conditions, resulting in erroneously high formaldehyde emission rates. Our results, however, show successful separation of these two species, allowing for simultaneous determination. In this study, a method is developed for the simultaneous determination of carbonyl and NO2 by HPLC with either a PDA or a UV-Vis detector following DNPH cartridge collection. Exhaust emissions of carbonyls and NO2 are determined for HDD trucks and transit buses tested under several fuel and after-treatment device combinations on a chassis 10.1021/es0353356 CCC: $27.50
2004 American Chemical Society Published on Web 10/16/2004
TABLE 1. Testing Project and Vehicle Information project name CMAQ
dates, participants, locations summer 1999 vehicle testing: NYSDEC, WVU facility & equip.: NYCDEP, NYSDEC WVU, NYSDOH
vehicles type HDD truck
transit bus February 2000 diesel bus vehicle testing: ERMD, NYSDEC facility & equip.: ERMD, NYSDEC, NYMTA, Johnson Matthey CSD, Corning Inc., Equilon Enterprises LLD, RAD Energy Corp. April 2001 CNG & hybrid bus vehicle testing: ERMD, NYSDEC facility & equip.: ERMD, NYSDEC, NYMTA
N
engine type
35 Caterpillar Cummins Ford GM International MACK Mitsubishi Navistar Renault
emission control
fuel
test cycles
OEM
diesel
3 Orion V DDC 6V92
OEM & CRT
diesel CBD sulfur: NYBus 30 ppm 300 ppm
2 Orion V DDC series 50
OEM & CRT
3 New Flyer OEM DDC series 50 CNG 1 Orion OEM diesel/electric hybrid
CNG
WVU 5-mile TEST-D
CBD NYBus
diesel
a CBD, central business district driving cycle; NYCDEP, NY City Department of Environmental Protection; CMAQ, congestion mitigation and air quality; NYMTA, New York Metropolitan Transit Authority; CRT, continuous regenerating technology; NYSDEC, NY State Department of Environmental Conservation; DDC, Detroit Diesel Corporation; NYSDOH, NY State Department of Health; ERMD, Emissions Research and Measurement Division, Environment Canada; OEM, original equipment manufacturer; NYBus, New York bus driving cycle; TEST-D, Test-D route driving schedule; WVU, West Virginia University.
dynamometer over different driving cycles. The transit buses tested include diesel, diesel/electric hybrid, and CNG buses. Diesel transit buses, including diesel with the original equipment manufacturer (OEM) muffler and diesel with CRT particle trap, were tested with regular (∼300 ppm of S) and ultra-low sulfur (
