Environmental Air Monitoring

Transcription

1 Environmental Air Monitoring Dr Caroline Widdowson Material Emission Specialist Dr Nicola Watson Environmental Specialist

2 What do we mean by air monitoring? Whichever vapour-phase organic chemicals are of interest Whether or the it s most VOCs in whale polluted breath air on the planet Photograph courtesy of: Dr. Rei Rasmussen, Oregon Graduate Institute, USA

3 Air Monitoring Applications Include: Soil gas and vapour intrusion assessments Mapping criteria pollutants in ambient air, diurnal changes Atmospheric Research In situ monitoring of underground contamination

4 Air Monitoring Applications Include: Landfill gas monitoring Odorous industrial emissions Indoor air quality and tracer gases used for ventilation studies Biogenic emissions

5 Analytical Instrumentation - UNITY C (TD-GC/MS)

6 Thermal Desorption; one versatile technique for all vapour phase air monitoring applications Electrically-cooled focusing trap On-line Canisters/Bags Sorbent Tubes Passive Active Water and volatile interferences may be purged to vent µl injection of vapour into GC(MS)

7 Sorbent Tubes: Sampling Techniques Active Sampling Passive Sampling Which method do I use?

8 Active (Pumped) Sampling Pump air through sorbent tube Flow Rate = ml/min Volume = 500 ml 100 L Much faster technique compared to diffusive sampling Important do not exceed breakthrough volume for a compound on a given sorbent Pump

9 Tube Based Thermal Desorption An Overview of the process Sorbent Material Sample Matrix e.g. Air

10 Tube Based Thermal Desorption Sample passes onto the sorbent Compounds of interest are adsorbed on the sorbent surface

11 Tube Based Thermal Desorption Lighter gases such as nitrogen pass through the sorbent

12 Air Monitoring - Pumped Sorbent selection for both tubes and focusing trap are very important Semi volatile compounds - Weak sorbent Helps prevent retention of unwanted compounds Very volatile compounds - Strong sorbent Prevents breakthrough of light compounds

13 Common Sorbents Sorbent Name Volatility Range Water retention Quartz wool / silica beads C 30 - C 40 Tenax TA C 7 - C 30 Carbograph 2TD C 8 - C 20 Carbograph 1TD C 5/6 - C 14 Carbopack X C 3/4 - C 6/7 UniCarb C 3 - C 8 Carboxen 1000 C 2 -C 5 Carbosieve SIII C 2 -C 5

14 Does selection of sorbents leave you feeling confused? Don t worry Agilent has the information Which sorbent for which compound or range of compounds? What about breakthrough? you need, whatever your application My sample has high humidity what sorbent do I use? Is the sorbent compatible with the conditions?

15 One complex example (US EPA TO17) Splitless desorption of Air Toxics tube loaded with 1 L of 1 ppb std GCMS Source: TDTS 86

16 TD isn t just for trace levels: High-concentration industrial emission samples Re-analysis Re-analysis Sample Pumped sampling of 1 L stack gas with TD-GC/MS analysis Sample splitting during both primary (tube) and secondary (trap) desorption. Total split ratio: 3000:1 Quantitative re-collection of both splits allows repeat analysis for confirmation

17 Not just volatiles... Benzo(a)anthracene Chrysene Benzo(b)fluoranthene Benzo(k)fluoranthene Indeno(1,2,3-cd)pyrene Benzo(g,h,i)perylene C 14 C 16 Benzene Re-collection C 18 Diethyl phthalate Dimethyl phthalate Dibutylphthalate Di-n-decyl phthalate C 20 C 24 C 28 C 32 C 36 C 40 Toluene Hexadecane Sample D-ethyl-hexyl phthalate Benzo(a)pyrene Re-collection Dibenzo(a,h)anthracene Re-collection PCB s Aroclor 1260 Sample Sample

18 Passive (diffusive) sampling Diffusive sampling = a simple and cost effective method of collecting the large number of samples required in many air monitoring programmes Vapours migrate across the air gap at a constant uptake rate Diffusive sampling is a slow process, typically sample for days Ambient conc. of vapours in the environment Brass Cap Diffusion Cap (fitted to grooved end of tube) Zero conc. of vapours at the sorbent surface Air gap

19 When should I use diffusive sampling? You know the compound that you are looking for There is a validated uptake rate available for that compound The test atmosphere is not heavily contaminated with a wide range of other organic compounds at much higher concentrations The expected concentration of analyte in the atmosphere is such that the desired sampling time (usually between 4-8 hours (occupational) and 1 to 4 weeks (environmental)) will result in a mass on the tube which is above the limit of detection of the TD / GC(-MS) method. If you are looking for several compounds of differing volatility x x x x You are using a multibed sorbent tube You are sampling a complete unknown atmosphere You want to sample two (or more) compounds of widely differing volatilities (e.g. acetone and toluene). There are no uptake rates available for the compounds of interest

20 Using Sorbent Tubes for Diffusive Sampling of Outdoor Air Mapping urban pollution concentrations with low-cost diffusive (passive) sampling sampling sites - black dots Yellow dots = pollution hot spots 1 TDTS 10 Use of diffusive sampling with TD-GC for ambient air monitoring

21 Typical applications: Passive sampling for air monitoring in industry Workplace air monitoring (Occupational hygiene) Industrial perimeter monitoring Stack and fugitive emissions Monitoring guidelines (sorbents, uptake rates, sampling volumes, etc.) available from standard methods (and from Markes)

22 Easy-VOC Simple sampling for VOCs in air Grab sampling for sorbent tubes: Reliable sampling of 50 or 100 ml volumes (or multiples of same) Kit contains: hand pump and 10 conditioned & capped sorbent tubes Main features Ease of use great for inexperienced personnel Humidity effects Negligible Breakthrough? Minimised Calibration? Not required Easy-VOC - For soil gas, indoor air, workplace air & stack gas. Also the perfect complement to high sensitivity GC detectors

23 Comparisons of Easy-VOC with standard pumped sampling Comparison with FLEC constant flow pump (Black) and Hand pump (Red & Blue) equal performance

24 Can sorbent tubes do everything? Great for C 3/4 to C 40 compounds x NOT suitable for ultra volatile compounds such as CF 4, C 2 H 2, H 2 S Ambient temperature trapping is not enough, sorbents require cooling to retain these compounds Samples collected online or in Canisters

25 Online sampling applications Ambient Air Zero Air Standard Gas A three sample channel system can be used to alternate between sample, standard and blank gases facilitating automatic calibration and unattended operation of the system.

26 Performance of the system Ethane Key: Blue (3 am) Red (12 noon) Green (5.30 pm) Ethene 1-Butene Acetylene 2-methylpropene Pentane Propane Propene Butane Quantitative Retention of Acetylene from 1500 ml of Air without Liquid Cryogen Plot of peak area against volume sampled for acetylene Sequence of Analyses of Ozone Precursors in Suburban Air Using a Single Column Splitless analysis of 500 ml of ambient air (courtesy of Ecole des Mines de Douai)

27 Fixed and Mobile sites Fixed sites now well established. Recent increase in mobile sites requiring analysis of ozone precursor compounds Advantages to this are that the mobile sites can provide additional data on days when exceedances are high Not only ozone precursor analysis, the system can also analyse H 2 S, mercaptans and some of the volatile GHG s (N 2 O, SF 6, CF 4 ).

28 5975T LTM GCMSD Out of Lab & In the Lab Transportability An integrated GREEN GC-MS system for mobile lab Power consumption 46%, Footprint 38%, Weight 35% Anti-vibration design and test for transportability Faster analysis on site LTM column module for faster separation Use DRS-RTL for faster screening Agilent lab GCMSD performance 5975C performance Supports Dual-use capability: Out of Lab & In the Lab

29 Application: Ultra Volatile Greenhouse Gases from Ambient Air (UNITY-Air Server ) CF 4 C 2 F 6 C 2 F 6 SF 6 N 2 O Extracted ion 69 Extracted ion 119 Extracted ion 127 Extracted ion 30 Target compounds: CF 4 (Carbon Tetrafluoride) C 2 F 6 (Hexafluoroethane) SF 6 (Sulphur Hexafluoride) N 2 O (Nitrous Oxide) Greenhouse Gas focusing trap at -30ºC and flow path at 120⁰C. Performance in field operation: Detection limits: ppt for SF 6 & C 2 F 6, 50 ppt (CF 4 ) and 200 ppt (N 2 O) Retention time stability: <0.1% RSD across all compounds Standard reproducibility: 0.8-5% RSD Excellent peak shape for splitless injection

30 Online monitoring of odorous sulphur compounds in ambient & industrial air (UNITY-Air Server ) Target compounds: H 2 S (hydrogen sulphide) CH 3 SH (methanethiol/me.mercaptan) C 2 H 6 S (dimethyl sulphide) C 2 H 6 S 2 (dimethyl disulphide) 3 channels with H 2 S focusing trap at -15 C to -30ºC and flow path at 80ºC. GC-FPD Performance in field operation: Detection limits: 0.15 ppb Retention time stability: <0.1% RSD across all compounds Gas standards at 20 ppb and 10 ppb levels Standard reproducibility: 0.5-5% RSD Recovery: >87% for all analytes

31 Canister Sampling Canisters have also been used to collect samples for analysis of these ultra volatile compounds Agilent's new CIA Advantage system Provides the solution for off- line analysis of ultra volatile compounds collected in canisters the same performance as online systems

32 Summary Whichever vapour-phase organic chemicals are of interest Whatever your air monitoring application Whether or the it s most VOCs in whale polluted breath air on the planet Photograph courtesy of: Dr. Rei Rasmussen, Oregon Graduate Institute, USA

33 Customers involved in Air Monitoring

34 Further information: Further information from Agilent/Markes Team Thermal Desorption Application notes Brochures Accessories and consumables catalogue Environmental applications guide