As pressure on air quality increases, flexible and dynamic techniques are required to understand variation in air quality. New mobile air quality monitoring techniques are allowing us to intensively describe air quality, rather than relying on fixed sites to provide a representative picture of air quality. Mobile monitoring allows more opportunity to assess air quality in an area, using temporary sites which can be moved around multiple locations.

Traditionally, air quality has been monitored using networks of fixed instruments, monitoring continuously in the same location. In order to build a spatial picture of how air quality varies in a given area, multiple sites are required to develop a meaningful picture. This approach works, but it is important to understand the limitations and extent of the representativeness of the data. In many areas, such as cities with heavy traffic volumes, urban canyons, varied weather and sporadic emissions, patterns of air quality will vary at a range of spatial and temporal scales, and a fixed network may miss this complexity. In other cases, there may be a need to quickly assess the extent of an air quality problem (for example diesel emissions) or to assess the effectiveness of a policy change. In some situations, a network may already be in place, but it may be limited, or have ‘holes’ which need filling. Similarly, there may be a need to understand an air quality question, but a permanent site, designed to operate forever, may not be justified, or more commonly, affordable! These are all examples of where mobile monitoring can help to build a clearer picture of air quality.

Broadly, mobile air quality monitoring involves deploying instruments for a short period at a temporary location, before moving them to another location. These deployments may be as short as a few hours or a few days. Often instruments are mounted in or on a vehicle, in a trailer or mounted temporarily. Regardless of the deployment, the site is treated as temporary, and the instrument is moved after a short period. Aeroqual instruments have been deployed for mobile air quality monitoring projects inside vans, on the roofs of vans, in pickup trucks and on temporary stands.

Simply put, you can cover more locations, quickly and more cheaply than deploying a fixed site. Air quality changes, and mobile monitoring allows you to respond to these changes quickly. An instrument in a van can be moved as easily as driving the van to a new location. An instrument on a stand can be packed up easily and then redeployed at the next site. If a network of sites already exists, then mobile air quality monitoring can be used to fill in the gaps between existing sites. Similarly, mobile monitoring can be a useful first step in assessing where to locate fixed sites in order to measure the highest concentrations of pollutants and maximise the value of the network. For example, let’s say you want to understand the characteristics of a small area – mobile monitoring allows intensive, small scale campaigns which enable detailed understanding of local air quality. Mobile monitoring can often work out cheaper than fixed monitoring. A fixed site will require a range of infrastructure to operate, including power connection, mounting and security arrangements – and all of this is fixed expense and is really difficult to move. Using mobile monitoring, the set up costs are shared across multiple sites – so the more sites that can be monitored with a mobile set up, the cheaper each one becomes.

Regulatory agencies often use mobile air quality monitoring for assessing new site locations and plugging holes in their networks. However these mobile sites are often regulatory sites ‘on wheels’ – they still require mains power, security and may often need a large area for deployment. They’re complex and need a lot of servicing and maintenance. Aeroqual’s instruments work well for mobile monitoring, as they are portable, robust and self-contained – they can be mounted in or on a vehicle easily and with only a power supply required. Let’s look at some examples.

In India, mobile monitoring techniques are being used to assess the impact of regulating traffic volumes in Delhi. A 15 day trial, where odd and even number plate vehicles are alternately excluded from the city is being undertaken to assess the potential impact on air quality across the city. 210 locations will be monitored in 15 days, using an instrument mounted on a small van. Monitoring on this scale is too complicated, expensive and time consuming to perform with fixed monitoring. Mobile monitoring allows vast areas to be covered in a relatively short timeframe.

In Greece, mobile monitoring is used as part of a wider environmental monitoring program for a large motorway, aiming to understand the impact of the motorway on air, water and noise. By mounting instruments in a van, the operators can assess air quality along the entire motorway, quickly and without needing a network on multiple sites. Concentrations can be assessed at different sections of motorway, for example at interchanges, under different traffic volumes and flows and at different times of the day.

In New York City, the Department of Environmental protection is using instruments mounted in a van to fill the gaps in their network, and to assess areas which they suspect may have air quality issues. The mobile van allows many locations to be covered, with no infrastructure required – it simply needs somewhere to park.

Recently, agencies have been using mobile monitoring as a way of understanding air quality impacts of industrial accidents and natural disasters. In Australia, mobile air quality monitoring has been used to measure Particulate Matter (PM) concentrations from a coal mine fire, and also from naturally occurring bushfires. By having a mobile system ready to go, agencies are able to respond quickly to an incident, whilst also having the flexibility to change their response if things change during the deployment.

The major consideration is mounting and housing the instrument. Often vans and enclosed trailers are used, as this increases the mobility of monitoring – simply drive to the next site! Consider also how you will power the instrument – many deployments use inverter and battery systems, or temporary mains connections. Aeroqual instruments can also be powered using photovoltaic (solar) panels and battery systems. You’ll also need to build appropriate bracketry to hold your instrument and pass inlets through vehicle roofs. This is straightforward but requires some planning – Aeroqual can provide guidance and assistance. If a vehicle is not being used then a tripod or a temporary bracket on a building or fence works well, and Aeroqual can help with this too.

This will depend greatly on the goals of the project. In some cases  a few hours may be sufficient, or in other circumstances a few days of monitoring may be required. There is no hard and fast answer here – it depends on what you are trying to capture. For instance, if you wanted to quickly understand an area, 24hrs at a handful of sites might be enough. If you were looking for a suitable location for a permanent site, then you might consider longer monitoring periods, to give a bit more certainty to the measurements. The longer the monitoring period at a site the more certainty there is in the data. The natural follow on question is how many sites do I need? Consider the number of people exposed in the area of interest, and the diversity of sources in the area – more complex emissions will require more sites to completely understand. Similarly, where more people are exposed, more sites may be needed to understand any variation.

For projects monitoring urban emissions, which may include a range of pollutants then the standard suite of PM_2.5, PM­₁₀, NO₂ and CO is a good start. If a contribution from industrial emissions or from coal burning is expected, then consider adding O₃, VOC and SO₂. For targeted, small campaigns, like diesel emissions in a city centre, you may only be interested in a single parameter, like NO₂. Rapid response projects, like those measuring the impact of wildfires, may only measure PM_2.5 and PM₁₀, as these are likely to be the key emission from the source. Similarly, the parameters measured in an industrial fence line study, should be tailored for the emissions expected. The benefit of Aeroqual instrumentation is its flexibility –parameters can be added later as needs change. Don’t overlook adding meteorological parameters too – having reliable wind speed, wind direction and temperature data can greatly improve the usefulness of any data and can help in understanding the study area more fully.

Will the project or customer be satisfied with qualitative or indicative data, or is a more rigorous plan for quality assurance and calibration required? Mobile monitoring projects can yield the same high quality data as fixed projects, but since the instruments are frequently moved, care should be taken to plan appropriately for stabilisation, calibration and maintenance. Remember to keep detailed records of where  sites are located, how long they were there for and start and finish times. GPS can be integrated into Aeroqual systems too, and this can help manage the location data.  A suggested approach may be to allow time at each new location to perform checks as needed. Remember to allow more travel time to access  sites, or it might not be practical to access sites at all times of the day – especially if there is traffic to contend with!

If you need to understand how air quality varies across an area at small scale, fill the holes in your existing network, or want the capability to easily move your instruments around, then mobile air quality monitoring could be a great solution. Check out Aeroqual’s range of instruments – all of which are perfectly suited to mobile monitoring campaigns. Get in touch with us here and we can help you with all your mobile monitoring needs!