Particulate Matter monitoring – PM10

What is PM₁₀?

“PM”, Particulate Matter, is not a single pollutant, but refers to a complex mixture of solids and aerosols of varying shape, size, and chemical composition and may contain many chemical species like organic compounds, inorganic ions, metallic compounds, elementary carbon, etc. These atmospheric particles are defined by their diameter for air quality regulatory purposes.

The inhalable particles that are less than or equal to 10 micrometres in diameter are collectively known as PM10. They tend to settle as they are heavier. Once released, they stay in the air for minutes or hours and travel as little as 100 meters to 50 kilometres. Examples of such coarse particles include construction dust, pollen, mold, etc.

Sources

Particulate matter PM₁₀ are either directly emitted from a source (primary PM) or are formed through the chemical reactions of gases such as oxides of sulfur (SO_x), nitrogen oxides (NO_x), organic compounds, etc. in the atmosphere (secondary PM). The natural sources of particulate matter are wind-blown dust from open land, pollen, spores, mold, dirt, soil erosion, and forest fires. Anthropogenic sources of PM₁₀ include:

• Burning fossil fuels such as gasoline, oil, diesel or wood, 
• Waste burning
• Dust emitted from unpaved and paved roads
• Crushing and grinding of rocks
• Uncontrolled construction activities
• Dust from factories, agriculture, landfills
• Emission from energy supply and industrial processes
• Metal and steel production as well as the reloading of bulk material 
• Wear and tear of brakes and tires of vehicles
• Organic compounds from industrial processes and motor vehicle exhaust

Permissible levels of PM₁₀

The breakpoints concentrations describing the quality of air based on the PM₁₀ concentrations for different countries are given below. In India, the daily average PM₁₀ levels of up to 100 μg/m³ are considered satisfactory. The Air quality guidelines by the World Health Organization suggests a 24-hr mean of 50 μg/m³.

Breakpoints of PM₁₀ (μg/m³)

Table: Breakpoints of PM₁₀ (μg/m³)  

India (24-hr)	US (24-hr)	China (24-hr)	EU (8-hr)
AQI Category	Break point concentration	AQI Category	Break point concentration	AQI Category	Break point concentration	AQI Category	Break point concentration
Good	50	Good	50	Excellent	50	Very low	15
Satisfactory	100	Moderate	150	Good	150	Low	30
Moderately polluted	250	Unhealthy for sensitive	250	Lightly Polluted	250	Medium	50
Poor	350	Unhealthy	350	Moderately Polluted	350	High	100
Very Poor	430	Very Unhealthy	420	Heavily Polluted	420	Very high	100+
Severe	430+	Hazardous	420+	Severely Polluted	420+

Health & Environmental Impact of PM₁₀ 

Health Impact

The potential of the particulate matter to affect human health depends directly on the size of particulate matter. The particles with < 10μm diameter generally pass through the nose and throat and enter the lung. PM₁₀, although being less of an immediate health concern than PM_2.5 due to its size, is still small enough to pass through the nose and throat and enter the lungs.

When inhaled, PM₁₀ deposits on the surface of the airways in the upper region of the lung, inducing tissue damage, and lung inflammation. It can irritate the nose, throat, and even eyes. Short term exposure to PM₁₀ aggravates already present respiratory diseases such as asthma while long term exposure can affect respiratory mortality. Sensitive groups of people such as children, elderly with chronic heart or lung disease, or people suffering from asthma are more susceptible to adverse health effects of particulate exposure. 

Environmental Impact

The major environmental impacts of PM₁₀ pollution are visibility reduction and deposition. High levels of PM₁₀ causes visible air pollution affecting the aesthetics of the surrounding environment. The settling of the air-borne PM₁₀ on plants, soil, and water ecosystems have harmful effects on them. The metal and organic compounds reduce plant growth and yield while the deposition of PM into water bodies affects its quality and clarity. 

Atmospheric particles affect the heating and the cooling of the atmosphere. Some components of PM such as black carbon promote climate warming while some components such as sulfates and nitrates have cooling properties. 

Possible corrective measures 

The primary step is PM₁₀ monitoring to identify the areas with high particulate levels or areas where air quality does not meet the PM₁₀ national standards.In addition to this, the following corrective measures can be taken:

• Limit outdoor activities and close windows and vents during times of high air pollution.
• Avoid keeping your vehicle idle for long. 
• Avoid areas with traffic congestions, construction activities, or unpaved roads. Breathing such polluted air daily also leads to health effects in the long run. 
• Eliminate the use of the fireplace, wood stove, gas-powered lawn, or garden equipment. 
• Eliminate open burning of leaves, trash or other materials

Measurement methods of PM₁₀ monitoring

Different working principles for particulate matter monitoring in the ambient environment are Gravimetric, TOEM, Beta Attenuation (BAM), and Laser scattering 

High-volume Gravimetric Method – The PM₁₀ monitors based on the gravimetric principle takes in the ambient air for 24 hours at a constant flow rate through a size-selective inlet that only allows particulate matter with an aerodynamic diameter of 10µm or less to pass through. The particulate matter is collected onto a pre-weighed filter conditioned at constant temperature and humidity conditions. After the 24-hour sampling period, the filter is conditioned again under the same temperature-humidity conditions and reweighted. The difference in the weight corresponds to the mass collected on the filter, which along with known flow-rate, sampling period, and the total volume of the air sampled is used to calculate the PM₁₀ concentration. 

Tapered Element Oscillating Microbalance (TOEM) – It is a proprietary system for particulate matter monitoring. The PM₁₀ monitors based on TOEM determines the PM₁₀ concentration by continuously weighing the particulates deposited on the filter attached to a hollow tapered element that oscillates in an applied electric field. The oscillating frequency decreases with the accumulation of particulates on the filters. Thermal mass flow controllers constantly control and measure the flowrate of the PM₁₀ monitor which along with the mass concentration, temperature, and other factors is used to continuously calculate the PM₁₀ concentrations. 

Beta Attenuation Monitor (BAM) – The PM₁₀ monitoring based on the BAM principle measures the particle mass density using beta radiation attenuation. The particulates in the ambient air drawn into the PM₁₀ monitor are deposited on a paper-band filter and exposed to beta rays (i.e. electrons with energies in the 0.01 to 0.1 MeV range) which gets attenuated as a function of the particulate mass. The beta count reduces with an increase in the PM₁₀ mass and is recorded by the detector and converted to concentration.

Laser Scattering – The PM₁₀ monitor based on the physical principle of light scattering, also known as optical particle counter (OPC), measures dust particles illuminated by laser light at a 90° angle. The light scattered from each particle is collected at approximately 90° by a mirror and detected by a photo-diode. This signal is then fed into a multi-channel size classifier where a pulse height analyzer is used to classify each pulse that is proportional to the particle size. The counts in the channel corresponding to PM₁₀ are converted to the concentration of PM₁₀.

Among all the above principles of PM₁₀ monitoring, PM monitors based on laser scattering are typically found to be preferred for ambient air monitoring as they yield quick and accurate measurements and are inexpensive in cor

Oizom’s working principle for PM₁₀ monitoring

Oizom’s DUSTROID is an online particulate monitoring system that measures the concentration of various particulate sizes ranging from 1 micron to 100 microns such as PM_1, PM_2.5, PM₁₀, and PM₁₀₀ in the ambient air. Our PM sensor works on the principle of laser scattering. The active sampling powered sensor-based air quality monitor DUSTROID is deployed across several cities, campuses, universities and is used for drawing actionable insights to tackle the rise in ambient PM₁₀ concentrations.

5 reasons why PM₁₀ monitoring is important:

• PM₁₀ is a complex mixture of solid and aerosols with a very small size that can easily pass through the nose and throat and penetrate the lungs.
• Particulate matter is emitted into the atmosphere from combustion processes, cruising or grinding of rocks, resuspension of dust and dirt from roads, soil, etc. They are also formed into the atmosphere from various chemical reactions of other air pollutants such as NO_x and SO_x. 
• When inhaled, it irritates the eyes, nose, throat, and the airways and can also lead to aggravation of respiratory diseases. 
• PM₁₀ monitoring is an efficient way to detect high concentrations of particulate matter and prevent high-level exposures. 
• Real-time monitoring of PM₁₀ levels helps in calculating air quality index to deliver health advisories as well as formulating an action plan to meet standards.