Control of Particulates and Indoor Air Quality

By: Nicholas Byczynski

Date Published: March 24, 2023

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Control of Particulates and Indoor Air Quality

AESG technical experts assist clients in delivering WELL Certified projects through design, construction and occupancy. WELL is a performance-based system for measuring, certifying, and monitoring features of buildings that impact human health and well-being through air, water, nourishment, light, fitness, comfort, and mind. By focusing on these elements, the WELL Standard aims to improve Indoor Air Quality (IAQ) in buildings.

One aspect of IAQ that is often under-served by standard design approaches, such as compliance with ASHRAE 62.1, is the control of Particulates, predominately PM 2.5 and PM 10.

Air Particulate Matter (PM) refers to a mixture of small solid and liquid particles suspended in the air and is not a single pollutant but rather a complex mixture of various chemicals. PM is categorised based on its particle size for air quality regulatory purposes, with PM10 referring to particles with a diameter of 10 microns or less that can be inhaled into the lungs and cause adverse health effects. PM2.5 refers to finer particles with a diameter of 2.5 microns or less.

Sources of PM10 and PM2.5 include combustion of gasoline, oil, diesel fuel or wood, dust from construction sites, wildfires, industrial processes, pollen, and bacteria. PM may also be formed in the atmosphere through chemical reactions of gases such as sulfur dioxide, nitrogen oxides, and organic compounds, which can be emitted from both natural and man-made sources. PM2.5 pollution is primarily caused by emissions from combustion, while PM10 includes a wider range of sources such as dust, industrial processes, and burning of waste.

Air quality has been directly correlated to a range of health problems in both the developed and developing work and according to World Health Organisation studies:

Ambient (outdoor) air pollution in both cities and rural areas was estimated to cause 4.2 million premature deaths worldwide per year in 2019; this mortality is due to exposure to fine particulate matter, which causes cardiovascular and respiratory disease, and cancers.

WHO estimates that in 2019, some 37% of outdoor air pollution-related premature deaths were due to ischaemic heart disease and stroke, 18% and 23% of deaths were due to chronic obstructive pulmonary disease and acute lower respiratory infections respectively, and 11% of deaths were due to cancer within the respiratory tract.

In modern economies people can spend between 80-90% of their time indoors between the home and the workplace and so it’s critical that healthy environments achieve low levels of Particulate matter, however very few local authorities or international guidance documents define requirements to measure and control these harmful Particulates in the built environment.

This is not the case with the WELL Building Standard which places IAQ as a core concept stating:

“Clean air is a critical component to our health. Air pollution is the number one environmental cause of premature mortality, contributing to 50,000 premature deaths annually in the United States and approximately 7 million, or one in eight premature deaths worldwide.”

The reactions people have to air pollutants vary widely and depend on multiple factors including the concentration of the contaminant, the rate of intake and the duration of exposure. Pollution source avoidance, proper ventilation and air filtration are some of the most effective means of achieving high indoor air quality. In the U.S., the Environmental Protection Agency (EPA) sets National Ambient Air Quality Standards (NAAQS) according to ongoing research and monitoring.

These Standards have been credited with dramatic improvements in outdoor air quality, and create exposure limits based on both duration of exposure and concentration for the six major air pollutants: carbon monoxide (CO), lead (Pb), nitrogen dioxide (NO₂), ozone (O₃), particulate matter (PM₁₀ and PM₂.₅) and sulfur dioxide (SO₂). The WELL Building Standard® expands upon these requirements by incorporating standards from additional agencies, such as the World Health Organisation (WHO). To help minimise transmission through contact with unsanitary surfaces, the WELL Building Standard provides an approach that combines the installation of appropriate materials with the implementation of effective protocols to regularly disinfect targeted areas.”

Unlike more commonly considered aspects of a healthy internal environment such as Temperature or Humidity the resultant particulate levels in a space are difficult to calculate during the design phase and are heavily influenced by construction quality, Facilities Management Operation and the micro-climate of the local area. Within this White Paper AESG will outline our approach to compliance with the WELL standard to achieve a Healthy internal environment in line with the guidance of the WHO and industry best-practice.

IAQ is often seen as the preserve of the MEP engineer and the Fresh Air system, and whilst they have a key role, a high quality internal environment with low Particulates is the responsibility of many other parties; client, contractor architect, façade designer, Facilities Manager, Building occupier and all the way to the cleaning staff.

To address these challenges AESG have worked with clients and the WELL team to develop a comprehensive approach to achieve the best possible IAQ in operation and to achieve the requirements of the WELL Standard.

This process comprises of the following:

  • Detailed Review of credits and their implications
  • Understanding of local Particulate Levels
  • Development of multi-path compliance methodologies
  • Post occupancy verification and mitigation

Particulate Control within the WELL Standard:



Control of Particulates is discussed in 3 areas of the WELL standard, Pre-Condition A01, Optimisation A05 and A12. Of these only A12 is a “prescriptive” requirement meaning compliance can be assured via design decisions prior to construction. A05 and A12 are “performance based” and therefore can only be confirmed after completion and operation of the building as part of the performance verification stage. This often raises concerns for clients as certification is contingent on achieving A05 but it is not possible to guarantee this during design. It is therefore critical that a well-considered and holistic approach is taken from design through construction and operation to ensure that its achieved. 

A key first step in developing a Particulates control strategy is to understand the ambient air quality of the environment in which the project is to be constructed as this is out-side of the control of the project team but will influence the required design decisions. Obviously if the ambient Particulate levels are high, great effort will be required to achieve high quality IAQ than if the ambient air is extremely clean. A good resource is the WHO website which provides a database of ambient particulate levels around the world:

This data can then be compared to the recommended levels to ascertain the relative cleanliness of the ambient air, the current targets are annual mean values of 35 µg/m3 for PM2.5 and 70 µg/m3 with a planned reduction via interim targets to the Air Quality Guidelines (AQG) recommendations of 5 µg/m3 for PM2.5 and 15 µg/m3.

Source: WHO Global Air Quality Guidelines


Once the ambient conditions have been defined a comprehensive approach must be taken to controlling internal Particulate levels. AESG have identified 3 contamination routes and developed 4 key strategies control them which collective will help to ensure a healthy environment for occupants of buildings.

Source: AESG Particulate Control Strategy Map

Controllable Strategy 1: Source Control

As discussed previously it is not possible to directly control the ambient particulate levels but it is possible to develop methodologies to ensure that the generation of particulates within the premise are eliminated where possible or minimised and contained where they can’t be removed entirely.

The purpose of this strategy is to limit the development of PM 2.5 & PM 10 particulates within the occupiable spaces. The design team should review the space usages and develop a comprehensive strategy to limit the internal generation of these particulates. Examples of control methods may be: 

  • Elimination of smoking within the building 
  • No cooking in “open areas” or with sufficient ventilation to not impact permanently occupied spaces. 
  • Pressurisation control of any spaces with cooking 
  • Control of other particulate generating processes such as printing, spray painting or other similar operations, in well ventilated, negatively pressurised / sealed sub-spaces
  • Careful consideration of cleaning methods such as the use of HEPA Filtered Vacuum Cleaners by the Facilities team.

Controllable Strategy 2: Outdoor to Indoor Transportation – Air Tightness

The purpose of this strategy is to limit the transfer of PM 2.5 & PM 10 particulates from the external environment into the occupiable spaces themselves via uncontrolled infiltration. 

The consultant team should review the external air quality anticipated and develop a comprehensive strategy to limit the transportation of these particulates. Examples of control methods may be: 

  • Air-tightness of external façade elements – What is the anticipated Air Change Rate and how will the internal conditions be impacted by the ambient particulate counts. 
  • In areas with High levels of particulates it may be necessary to improve the building façade air tightness, particularly on facades that will see higher wind pressures during periods with high ambient particulate levels. It is highly recommended that the design performance is then validated via envelope commissioning as part of the construction process.
  • Revolving doors or Air curtains at primary entrances
  • Air seals on all secondary entrance routes
  • Positive pressurisation of the building via the Mechanical Ventilation system

Controllable Strategy 3A: Outdoor to Indoor Transportation – Air Filtration

The purpose of this strategy is to limit the transfer of PM 2.5 & PM 10 particulates from the external environment into the occupiable spaces themselves via the Mechanical ventilation system. 

The consultant team should review the external air quality anticipated and develop a comprehensive strategy to limit the transportation of these particulates. 

For Mechanically ventilated spaces air filtration is a critical method to control the PM 2.5 & PM 10 levels in the supply air. Determining the required level of filtration should also consider the ambient particulate levels in the project area. 

It is noted that EN 779 Filter standards are being phased out and should not be considered as part of the project specification with EN ISO 16890 is the preferred standard although ASHRAE 52.2 – MERV standards may also be but the differences in testing methods mean it is not possible to directly compare the two approaches and filter grades.

Eurovent 4/23 offers guidance on alignment between out door Air Quality and Indoor Air Quality Requirements as shown below:

Controllable Strategy 3B: Outdoor to Indoor Transportation – Active Control

The purpose of this strategy is to limit the transfer of PM 2.5 & PM 10 particulates from the external environment into the occupiable spaces themselves via the Mechanical ventilation system. 

The consultant team should review the external air quality anticipated and develop a comprehensive strategy to limit the transportation of these particulates. Examples of control methods may be: 

  • Active Control. The levels of both internal and external PM2.5 and PM10 levels could be monitored with control regimes implemented to either alert users of high ambient particulate levels or to reduce Fresh Air Quantities during periods of lower occupancy but high ambient particulate counts. Careful Consideration must be given to all other factors such as CO2 concentrations in the breathing zones as well internal temperature and humidity levels
  • Flushing of spaces can also be considered during periods of low ambient particulate counts.

Active control strategies can introduce significant complexity into the HVAC design requirements requiring variable volume Fresh Air systems and calibrated sensors within the occupies spaces and as such should only be considered for projects in highly polluted environments or in situations where very levels of internal air quality are proposed. It is recommended that the commercial feasibility of this strategy be assessed carefully during the early stages of the project.

Controllable Strategy 3C: Outdoor to Indoor Transportation – Building Pressurisation

Mechanical pressurisation is the only contributor to infiltration of ambient air, and therefore ambient particulates, that the HVAC designers have specified control over. It occurs when the building’s air handling system is controlled in a manner that intentionally introduces a higher quantity of outside air into a building than the quantity of air exhausted and relieved so as to achieve a positive internal pressure with respect to the external environment.

3 common methods of pressurisation control employed in buildings are: 

  • Manually balanced — no dynamic control. This is the most commonly employed method and involves the air flow in each space being fixed so that the Supply Air Volume is in excess of the Exhausted Air typically by up to 10% of the flow. 
  • Differential Pressure based control. This method requires Differential Pressure Sensors (DPS) to be provided to monitor the relationship between the internal and external pressure with the volume of air exhausted modulated to achieve a defined Differential Pressure – typically 5 – 10 Pa. Historically DPS control has been complex to commission and operate requiring sensors that are accurate at low DPs and sited carefully to negate the effects of wind. Future calibration of external sensors must also be considered. 
  • Airflow offset based control. Is employed where the Supply Air volume varies, for example in a Demand Control Ventilation system with the exhaust air volume modulated to ensure a fixed differential between the supply and return. 

Controllable Strategy 4 – Indoor Active Control

The purpose of this strategy is locally remove the Particulates from a space via a permanently or temporarily installed filtration system to actively control the PM2.5 and PM10 particulate levels to a given criteria. 

  • Install standalone – ePM1 90% (MERV 16) filters in recirculating units that can be deployed in spaces registering higher particulate counts based on an active control system
  • Permanently install additional filtration on recirculating AHUs or filter modules within ceiling voids based on an active control system monitoring of space Particulate counts.

This approach will ensure required particulate counts but will result in increased CAPEX and OPEX costs to the project due to the powered associated with the installation of the fan powered filters and the associated filter replacement cost and as such should only be considered for projects in highly polluted environments or in situations where very levels of internal air quality are proposed. It is also viable for retrofit situations where it may not be possible to implement Strategy 2 or 3 due to the challenges in modifying existing Air Handling plants or existing façade systems.


Control of Particulates in a buildings is a process that starts in design and continues through construction and into operation and requires input from many project stack holders. It is often assumed to be under the sole control of the MEP team but this is only a part of the story.

The achievement of WELL certification is performance based and so must be validated by a certified testing and verification agency after occupation of the building, on going recertification  is then required  every 3 years post award.

AESGs unique combination of WELL certification and engineering expertise can support you through all stages of the WELL process to ensure the highest standards in IAQ are achieved.

How can AESG help?

AESG is a specialist consultancy, engineering and advisory firm with offices in London, Dubai. Riyadh and Singapore working on projects throughout Europe, Asia and Middle East. We pride ourselves as industry leaders in each of the services that we offer. We have one of the largest dedicated teams with decades of cumulative experience in sustainable design, fire and life safety, façade engineering, building commissioning and digital asset management, waste management, environmental consultancy, strategy and advisory, acoustics, cost management and carbon management.

Nicholas Byczynski

Director of Sustainable Engineering, AESG

Nicholas is AESG’s Director of Sustainable Engineering. He is a Fellow of CIBSE with 14 years’ experience in the Middle East leading the Engineering teams in the design of high value projects across a range of sectors, particularly hospitality, residential, public amenities and retail. Nicholas has extensive experience managing large teams in multiple geographical locations with experience in the delivery of diverse projects from a 500,000m2 Hospital projects, signature buildings at the Expo 2020 site and an iconic Museum project currently under construction.

At every opportunity Nicholas has embraced low energy building design with sometimes pioneering use of a range of sustainable building techniques including natural ventilation, solar thermal, PV, Rain water recycling, concrete core cooling and advanced chiller system integrated controls. During his career he has led MEP teams to deliver multiple LEED gold and Platinum projects achieving major energy savings through carefully engineered solutions tailored to the specific project need. A focus on option selection and testing ensured all ideas were robustly assessed to deliver the sustainable, operational and commercial aspirations of the projects undertaken.

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