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 ozone precursors and other ultra-volatiles in areas affected by significant ground-level ozone pollution.
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 monoterpenes (α-pinene and β-pinene).
Although it is not compulsory to monitor all 63 species, there is a general desire in the analytical community to ‘future-proof’ analytical systems, by ensuring that polar compounds as well as hydrocarbons can be monitored simultaneously.
PAMS scheme re-engineering
Much of the air monitoring equipment in the current PAMS network uses relatively old technology that is in need of updating, so the stipulations have recently been ‘re-engineered’ in order to better handle present-day analytical requirements.
The revised scheme came into force in June 2019.
Although the requirement for a TD–GC system naturally remains in the re-engineered scheme, decisions on any new instrumentation used are referred to the individual monitoring agencies.
Complying with PAMS
The growing need to include polar species in PAMS monitoring schemes presents a challenge to analysts because of the tendency for volatile polar species and monoterpenes to be lost when conventional Nafion dryers are used to remove humidity.
However, Markes’ on-line UNITY–Air Server-xr thermal desorption systems offer an alternative system for water management – the Kori-xr module. This removes water using a trap-based system that does not affect recovery of polar species or acid-labile analytes such as monoterpenes.
The performance of Markes’ equipment has been recognised in independent laboratory and field trials commissioned by the US EPA. In particular, they demonstrated 100% target compound coverage, very low levels of instrumental bias and excellent precision between replicate measurements.