Mercury in Ambient Air is now routinely measured in both urban and rural sites due to the toxicity and mobility of this element. In addition workplace air monitoring for mercury and cell room monitoring are essential to protect the health of the workers in the relevant industries.

Mercury Analysers for these applications can be Online Mercury Monitoring Stations which are designed for fixed long periods of unattended operation, or Offline Analysers which are manually operated with traps exchanged on a daily to monthly basis and which allow flexible sampling points.

The essential differences in these applications are the level of mercury expected, the sample collection time and the frequency of collection.

Ambient air sampling usually involves looking for lower levels (0.5 to 5ng/m3) of mercury which do not tend to change significantly over time (except in cases of sudden pollution). Sampling times are typically 5 to 30mins for online measurements and daily to monthly for remote sampling.

For workplace air sampling, the levels are usually higher (0-50µg/m3) and more prone to sudden fluctuations therefore shorter sampling times are used with a higher frequency of sampling.

The Online Analysers can be tailored to exact requirements but generally can be split into two formats:

1. Free standing modules which can be set up in a stack at a suitable location or mounted in racks supplied by the customer
2. Fully integrated systems like the PSA 10.680 Mercury Analyser which is based on the PSA 10.525 Sir Galahad and can include automatic calibration, validation and multi-channel operation with preset alarm facilities.

A Passive Sampling Approach

Of course, online systems require power and gas utilities and are more costly than simply manual sampling. Manual sample collection, however, usually requires a worker to physically go to the sampling site, spend some time collecting the sample before returning the sample for analysis. For ambient air large sample volumes are required especially in unpolluted/pristine areas making the task even more difficult. As we know manual sampling is subject to incomplete, infrequent and fragmented data sets as well as significant personnel resources to carry out the sampling in the first place.

One interesting approach that PSA has developed is to deploy passive samplers. We use our existing Amasil (gold on Silica) trap technology to passively collect Hg from the ambient air over a period  (generally a few weeks to a few months). After this time the traps are collected and returned to the laboratory for analysis by the 10.525 Sir Galahad II The simple Amasil trap holder is shown below and may be mounted on any number of convenient structures. The design ensures protection from the elements (e.g. rain, wind or snow) and wildlife. This versatile approach offers the ability to deploy the traps in remote areas which are unreachable by traditional monitoring stations and can provide a complete temporal Hg concentration profile.

An Active Sampling Approach

The G525S100 Air Sentinel is an unattended ambient air, active sampling device that provides sampling with an accurate air volume for mercury in air studies. The ambient samle is actively carried over PSA's gold Amasil™ traps to preconcentrate any Hg that may be present. The air is actively pumped through the Air Sentinel using a calibrated micro vacuum pump. Depending on the location remoteness and other requirements the system may be powered by using a DC power pack, or the integrated rechargeable battery back with solar panel options.

The offline systems are available in different options depending on the customer's needs;

• The mercury in the air is trapped on an Anasorb trap. The trap is digested and the total mercury measured using CV-AFS with a PSA 10.025 Millennium Merlin. This approach is typically used for occupational exposure.
• The mercury in the air is trapped on an Amasil trap. The mercury is desorbed from the trap with heating and measured using a PSA M035S100 scarifier unit connected to a PSA 10.035 Millennium Merlin 1631.
• The mercury in the air is trapped on an Amasil trap externally at a remote site with pump and flow meter. The trap is then returned to the lab and the mercury is desorbed from the tube by heating within the PSA 10.525 Sir Galahad and measured by the atomic fluorescence detector.

Hg Concentration

If ambient air at single location over long period is required then online system is preferable depending on degree of automation required.

If workplace air at single location or at multiple locations is required then sampling frequency is usually expected to be high. This means the most automated system is the best option. Workplace air at various locations within a site really depends on number of locations, length of sample lines and sampling rates required.

If you require any further information on Mercury in Ambient Air or any other application, please complete our Information Request Form.

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