Since 1993, the US EPA network of Photochemical Assessment Monitoring Stations (PAMS) has required US states and local environmental agencies to use TD–GC systems to measure volatile organic ozone precursors in areas affected by significant ground-level ozone pollution.
But an increased need to ‘future-proof’ analytical systems, together with the requirements of the 2019 PAMS ‘re-engineering’ scheme, have placed pressure upon analysts to improve system performance.
What compounds are covered by PAMS?
A total of 63 compounds are listed under PAMS, with the bulk of these being volatile aliphatic and aromatic hydrocarbons.
However, there are some notable exceptions, which include polar species (formaldehyde, acetaldehyde, acetone, ethanol and benzaldehyde) and two acid-labile monoterpenes (α-pinene and β-pinene). These are more challenging, because they tend to be lost along with the water when Nafion dryers are used to dry the sample prior to analysis.
This difficulty is recognised within the PAMS method by the fact that it doesn’t require all these species to be monitored. Nevertheless, analysts are increasingly requesting the ability to handle the full list, in order to ‘future-proof’ their systems.
PAMS scheme re-engineering: Auto-GC systems
Formerly, much of the air monitoring equipment in the current PAMS network used relatively old GC technology that was struggling to cope with present-day analytical requirements.
Therefore, as part of the ‘re-engineering’ of the PAMS scheme that came into force in June 2019, new stipulations were published that strongly recommended the use of "auto-GC" equipment, such as Markes’ automated on-line TD–GC thermal desorption systems.
As previously, decisions on any new instrumentation used are referred to the individual monitoring agencies. However, Markes’ equipment was the top-performer in independent laboratory and field trials commissioned by the US EPA to advise analysts on instrument selection, with highlights being 100% target compound coverage, very low levels of instrumental bias, and excellent precision between replicate measurements.
The Markes/Agilent auto-GC systems also performed best in 2023 proficiency tests run by Battelle which tested 29 out of the 43 monitoring sites. Other systems running in the network had 20% - 33% of results returned deemed unacceptable whereas the Markes systems only returned 7% unacceptable results proving them to be significantly more reliable in the field.
Improving PAMS water management
To further improve the ability of Markes’ equipment to monitor polar species and monoterpenes as part of the PAMS scheme, an alternative to conventional Nafion dryers was needed. Addressing this demand is Markes' Kori-xr module, offered alongside Markes’ TD–GC systems for PAMS analysis.
Unlike Nafion dryers, Kori-xr efficiently removes water using a trap-based system that does not affect recovery of polar species or acid-labile monoterpenes – ensuring reliable results across the whole PAMS compound range. Performance improvement was also seen for retention time stability of “roaming” compounds like acetylene (ethyne) when using Kori-xr compared to Nafion.
Migrating from helium to hydrogen carrier gas
Helium shortages, and the consequent increase in costs, present a challenge to all GC users, and PAMS analysts are particularly affected because of the need for 24/7 monitoring during the monitoring season.
However, hydrogen is becoming an appealing alternative as a carrier gas for GC, because it is simple to generate on-site and on-demand using just water and electricity.
To provide this option for Markes’ PAMS customers, our systems are now fully ‘Multi-Gas’-enabled. This means that they are independently certified for operation with hydrogen (as well as helium and nitrogen), allowing analysts to reduce running costs and protect themselves against future helium shortages.
