Fine Particles: Why We Care

Transcription

1 Fine Particles: Why We Care Visibility/Radiative Forcing Health Effects A function of chemical composition PM2.5 Mostly 1) Sulfate 2) Carbonaceous - Organic - Elemental (Soot) 3) Metals, minerals, Metals, Minerals Organic Matter 40% Atlanta Aug PM2.5 = 31.3 µg/m3 Other 10% EC 3% Sulfate 34% Ammon. 12% Nitrate 2%

2 Eastern and Especially SE U.S. High PM2.5 Standard visual range for the period in units of kilometers. Visibility Information Exchange Web System, Sulfate mainly in eastern U.S.

3 1999 SO 2 Point Source Emissions Ohio River Valley x Source: EPA National Emissions Inventory Chloride: mainly > 2.5 um, sea-salt (Na, Cl - ), incineration Nitrate: NO 2 OH -> HNO 3g -> NO 3 - (neutral ph, low T, high RH) Sulfate: SO 2 OH -> H 2 SO 4g ->SO 4 2- ; SO 2 cloud drop -> SO 4 2-

4 Nitrate In Atlanta August 1999: EPA Supersite 4 Sat. Sunday NO 3 6:00 am to 10:00 am Nitrate, µg m UV Temperature, C 0 18:00:00:00 20:00:00:00 22:00:00:00 24:00:00:00 26:00:00:00 28:00:00:00 Day : HH : MM : SS, EST 5

5 Potential Gas/Particle Interactions at a Filter Surface ΔP Vapour Negative artifact (evaporation) Particle Positive artifact (absorption of vapour) Nitrate and other semi-volatile species (fresh OM) Issues: 1) Outdoor/Indoor heating/cooling sample & particles on filter, f(day/nite) 2) Pressure drop across filter

6 Collecting the particles on a filter inside We will have 2 channels - Ions acid/base denuder teflon filter -OC and EC (TC) activated carbon denuder and pre-baked quartz fiber filter Flow direction Filter Holder P 1 P 2 denuder Flow Control P a Vacuum Pump PM2.5 Size Selective Inlet (16.7 L/min) Critical orifice (P 2 /P 1 < 0.5) Issues 1) Blank filter load and unload into filter holder 2) Loading/unloading without touching filter 3) Measurement of flow rate at inlet at beginning and end of sampling 4) Keep track of sampling time (12 to 24 hrs) 5) Consider uncertainties (Δt, ΔQ, Δq, ΔSlope cal. curve, blank ) 6) Losses in sampling lines (Flow laminar/turbulent, diff. losses G/K)?

7

8

9 Extracting the Filters and Making Calibration Standards Extracting the filters (blank and loaded filter) 1. Transfer 30 ml of ultrapure (20 M-ohm) water into the vial using a graduated cylinder 2. Shake the vial for about 10 minutes or place in ultrasonic bath. 3. The liquid will be filtered and then analyzed by IC. Making Calibration Standards from a stock solution 1. We will make 4 standards: 0.1, 0.25, 1.0, and 2.5 mg/l from a stock solution containing 50mg/L of Cl -, NO 2-, NO 3-, SO 4 = (among other things) 2. Use an adjustable 1000 µl pipette and ml volumetric flasks. 3. Come to the lab knowing what volume will needed to be pipetted into each flask to get the correct concentration

10 IC Analysis

11 Ion Chromatography to Measure Anions Separation by our Column

12 Anion Exchange Column Interaction between stationary and mobile phases based on coulombic (ionic) interactions CO 3 = Cl - Stationary Phase with pos. ionic functional groups Sample Anions Cl -, NO 3-, SO 4 = Eluent Na 2 CO 3, NaHCO 3 (Na, H, CO = 3 ) Sample anions attach to stationary phase, are displaced by mobile phase, reattach, get displaced, and move through the column. Different anions in sample move through column at different rate separation of analytes.

13 Loading the sample loop 125 µl Sample Loop Separating the Anions 125 µl Sample Loop P Damper Valve P Damper Valve HP Pump Separation Column HP Pump Separation Column Degasser Sample Waste Suppressor Degasser Sample Waste Suppressor Eluent Conductivity Detector Waste Eluent Conductivity Detector Waste

14 Cyclone PM2.5 Activated C Denuder Thermal Optical measurements of TC (OC and EC) Sunset Labs Carbon Analyzer Optional denuder to limit positive artifact from gas absorption to quartz filter. He Purge Valve Particles thermally desorbed by a ramping T in a non-oxidizing environment (high purity He). Quartz Oven and Filter Laser Some organic compounds may be pyrolytically converted to EC (TOT method to monitors darkness of filter (pyrolized C) by transmission of laser through filter (also a TOR method) Vaporized organic compounds are oxidized to carbon dioxide and passed through a methanator to reduce the CO2 to methane, which is then quantified by a flame ionization detector (FID) Photo- Detector Gas Detector MnO2 Oxidizer Menthanator FID Valve Vac. Pump Oven cooled, then switch to a 2% oxygen/helium mixture, oven T stepped to 900C, original EC and that produced by the pyrolysis of organics during the first heating stages are burned in the presence of oxygen to form CO2... measured as methane Injection of methane standard as calibration check (tank of known mix of methane. Point during second heating cycle where laser beam transmission through the sample returned to the original sample transmission defines the split between organic and elemental carbon (the instrument response prior to this point being assigned to OC and after this point assigned to EC).

15 Example of NIOSH method Thermal Optical measurements of TC (OC and EC) Sunset Labs Carbon Analyzer

16 Issues with Measurements of TC, OC, EC Artifacts Adsorption of gases (use denuders, dynamic blanks)*. Loss of semi-volatile (sample for short period). Buildup of non-volatile material on collection surfaces over time (ash, refractory EC) Total Carbon (TC = OCEC) unambiguous. OC - EC split depends on methodology, temperature profile method to monitor pyrolized carbon (TOT, TOR), particle composition, (matrix effects) largest effect on EC since it is a small fraction of TC (EC highly uncertain, Lim et al. 2003). * Offenberg et al, Investigation of a systematic offset in the measurement of organic carbon with a semicontinuous analyzer. J. Air & Waste Manage. Assoc., : p ; Peltier et al, A. Sci. Tech, 2007

17 Analyzing the results Final Result: Cl - = A ± ΔA; NO 3 - = B ± ΔB; SO 4 2- = C ± ΔC Graph the calibration curve for each anion and cation and calculate the regression line slope (decide whether or not to force the slope through zero). Determine the uncertainty of the slope for each compound. Calculate the mean concentration and associated uncertainty of chloride (e.g., Cl - ± ΔCl - ), nitrate, sulfate, sodium, ammonium, in your sample using the calibration curve to determine liquid concentration of the filter extract, and the volume of liquid extract and sample air that passed through the filter to get an ambient concentration in µg/m 3. Consider any correction to the data due to blanks, sample losses etc. Discuss if these are or are not important (use numbers to support your arguments). Assume no uncertainty in the IC measurement (peak integration is perfect, and is directly proportional to conductivity in this IC). Do an ion balance, by comparing the concentration of the sum of anions to the sum of cations, in units of equivalents ( ug/m3 divided by MW multiply by valance) Attempt a mass balance by comparing the sum of the measured anions cations EC OM* to PM2.5 total mass. Use PM2.5 mass reported on the web to estimate mass during your filter sampling ( Make a pie graph? * Note OC must be converted to OM, use OM = OC * 1.6 (see Turpin and Lim AS&T 2001)

18 Final Notes Lab sign-up: you will have to sign up for 2 days. 1. Day 1: load the filter and start running (15 min) 2. Day 2: extract filter, calibrate IC and run sample (3hr), run OC EC