History depicts our early rejection of the plumes left by industrialisation. Perhaps J.M. Turner’s painting from 1832 is a living testimony, as it expresses his anger not only with social oppression but also with air pollution (Figure 1).

Figure 1: ‘Dudley’, J.M. Turner, 1832

Considering what we are up against today, we ought to be angrier than Turner; indeed, the situation has taken a turn for the worse. The various airborne contaminants we encounter (Figure 2) differ in their chemical and physical characteristics from those of the 1800s, but can be harmful even at low concentrations – it is, hence, vital for us to develop an in-depth understanding of air filtration.

Delegating the problem

A good place to start while looking at air filters is to consider their blind spots, not just their capabilities. Practically speaking, air filters require tools and conditions to work properly and to ensure there is no deviation in performance from the test report the manufacturer provided. Today, much of the air we inhale in residential buildings, offices, malls, hospitals, airports and cars is conditioned by HVAC systems. The characteristics of the air we breathe vary tremendously from one application to another, and we cannot blame the deterioration of air quality solely on one segment or invest all our research and development on one application.

The lion’s share of air conditioning systems

Globally, air conditioning constitutes around one-fifth of the total electricity used in buildings and is the second-largest source of global electricity demand growth after the industrial sector. In that context, the energy efficiency of HVAC systems is particularly important; by extension, the use of low-pressure-drop filters with enhanced efficiency is believed to be the order of the day in a non-pandemic situation.

In the pandemic mindset that has gripped us, though, there is much demand for an immediate retrofit to accommodate a High Efficiency Particulate Air (HEPA) filter, which in fact will lead to greater pressure drop. So, instead of blindly opting for HEPA filters, we must question whether our adherence to international standards that list HVAC and filtration guidelines is the issue, or if we need to make them fall under the analytical knife.

The substrata of change

To realign existing HVAC systems and air filters to fiercely defend our respiratory system, our plans to combat COVID-19 must be novel in approach and methodology. Initially, all pernicious practices must be ceased in terms of air conditioning and filtration maintenance. Debunking what is ailing our systems is an essential step in our troubleshooting method. My first article, 17 years ago, highlights the importance of air quality for our wellbeing, and the impact on health, if filtration is not granted due attention in the HVAC systems. Today, the daily death rates from COVID-19 suggest we have fallen harder and faster than we could have imagined.

While HVAC and air filtration technologies are essential for protecting health and ensuring wellbeing through providing contaminant-free air while maintaining thermal comfort, a cursory glance at fan-coil units (FCUs) reveals the use of a modest filter amidst a wide spectrum of pollutants. A detailed examination of a typical FCU catalogue reveals that only a few Pascals have been allocated for air filter installation and that the provision for improvement is rather limited.

The modesty of residential air filtration is not a trope. One can gauge the importance granted to residential air filters by ascertaining the space and thickness the designer allocates for them. Most residential systems rely on a single-stage filtration, which adopts the doctrine of washable filters.

The recent pandemic has emancipated our school of thought to install HEPA filters. Unfortunately, their installation is not as easy as their acquisition seems. The installation has to be preceded by a minimum of three filtration stages, namely, fresh air, pre- and fine filtration, which calls upon retrofitting or equipment replacement to accommodate the new pressure drop. In the past six decades, the focus of air filter specifications was to capture solid particles with medium efficiency for offices and shopping malls. Indeed, healthcare and non-healthcare facilities gave minimal attention to bioaerosols, gaseous and odour control.

Such inadequate attention has to be branded as counter-intuitive. Absolute Filters must be accompanied by a test report that certifies their compliance and rates their performance. The report acts like a birth certificate that states the performance characteristics of the filter. Clearly, filter selection ought to be based on providing the best aerodynamic design, in terms of efficiency, with the least resistance to airflow. We ought to employ characterisation tools to reveal what our lungs inhale and our eyes fail to trace. Once revealed what was, heretofore concealed, I am certain that there is no price we will not pay to attain the air quality that keeps us safe.

Furthermore, continuous urban aerosol monitoring can be critical to urban planning and to gauging suitable maintenance schedules while predicting filter-clogging times. Monitoring can prove to be invaluable for shopping malls, airports, places of worship, schools and supermarkets, where tremendous variations in human occupancy exist. Such variations may require an adaptive approach to provide the necessary filtration and HVAC tactics.

The blind spots of HEPA filters

I earlier spoke about HEPA filters. Before I elaborate on these special filters, it is essential to understand a few hard facts. A good start to inspire change in the air we breathe is to intrinsically understand the dynamics of filter performance. The novel coronavirus requires not only new tools but also novel attitudes to inquisitively assess the proposed solutions.  Particularly, the knowledge about COVID-19 is still evolving.

There is so much emphasis on using Absolute Filters to combat the virus. Numerous recommendations demand a higher class of HEPA filters to enhance air quality. However, it is important to highlight that appropriate Absolute Filter selection is equally important to provide the operating conditions needed to perform as designed. The parameters include face velocity, low particle concentration, low particle size distribution, and appropriate temperature and humidity levels.

Prior to finalising the specifications of HEPA or (Ultra-Low Particulate Air (ULPA) filters, a detailed account of the media properties used in their manufacturing must be forthcoming during the selection process by filtration consultants and/or engineers. Ultimately, appropriate filter selection should be delegated to filtration experts, who can be held responsible for their selection and the air quality we eventually breathe. The current pandemic has proven to us that filtration mistakes are not only expensive but can also be fatal. We lose ourselves when we compromise the principles we fight to defend, whether in terms of filter and HVAC selections or the preventative measures that never see the light of day. A filter specifications sheet carries no weight if it does not state the performance measures needed to outperform. Therefore, appropriate filter selection, operation and maintenance are of paramount importance.

Accepting and managing a new system

To dance the change, it takes more than a plan and a prudent approach. We must realise that yesterday’s approaches to tendering our way out locked us is a struggle or an exit strategy. We must believe in the need to reinvent the way we live and to capitalise on our knowledge and available technologies. In the past two decades, we did not dare to alter the quality of air we breathe; today, it is inevitable. What would the world be like if our powerful speech is heard by a conscious audience that is willing to advance? Perhaps the 16^th century political-philosopher, Niccolò Machiavelli was right when he described the courage needed to change: “It must be remembered that there is nothing more difficult to plan, more doubtful of success, nor more dangerous to manage than a new system.” Those words ring true even today.

Dr Iyad Al-Attar is an independent Air Filtration Expert and consultant on indoor air quality. He may be contacted at iyad@iyadalattar.com.