The Central Pollution Control Board (CPCB) has guidelines for ambient air quality analysis, including: Sampling and monitoring

The Central Pollution Control Board (CPCB) has guidelines for ambient air quality analysis, including: 

Sampling and monitoring

The CPCB recommends using a combination of manual and continuous methods at each monitoring location. The monitoring frequency should be at least 104 measurements per year, taken twice a week at uniform intervals. 

Pollutants to measure

The pollutants to measure depend on the location: 

Industrial areas: Measure RSPM/PM10 and SO2 

Densely populated and heavily traffic locations: Measure SO2, NO2, RSPM, SPM, and CO 

Areas with downwind flow: Measure ozone 

Methods

The methods used to measure pollutants can be physical, wet-chemical, or continuous on-line. · Data analysis

The CPCB analyzes data generated by State Pollution Control Boards (SPCBs), Pollution Control Committees (PCCs), and the National Environmental Engineering Research Institute (NEERI). 

The CPCB's National Ambient Air Quality Standards (NAAQS) aim to provide uniform air quality across the country. The NAAQS include 12 health-based parameters, such as PM10, PM2.5, SO2, NO2, CO, NH3, Ozone, Lead, Benzene, Benzo-Pyrene, Arsenic, and Nickel.

 

The ultraviolet fluorescence (UVF)

The ultraviolet fluorescence (UVF) method is a technique that measures the amount of sulfur dioxide (SO2) in a sample gas:

Irradiate the sample gas with ultraviolet radiation of a specific wavelength (190nm-230nm)

Flow the sample gas into a fluorescence cell

Detect the intensity of fluorescence 

The amount of light emitted reflects the amount of SO2 present in the sample. 

Here are some other uses of UV fluorescence: 

UV fluorescence photography

A full-spectrum light source, like the sun or a modified flash, is used to shine UV light at a subject. A filter in front of the camera blocks visible light, and the camera is modified to capture only UV light. The resulting images are in black and white. 

· · Excimer UV fluorescence

This technique uses a combination of ultraviolet light and a gas mixture to detect and measure trace amounts of chemicals and pollutants in samples such as air, water, and soil. 

Gas-phase chemiluminescence (GPCL)

Gas-phase chemiluminescence (GPCL) is a technique that uses chemical reactions to produce light energy, which can be used to detect and quantify volatile and gaseous components in the environment: 

How it works

Molecules emit light energy when they return to their ground state after being excited by a chemical reaction. 

·Applications

GPCL is used to measure the concentration of pollutants in the environment, such as nitrogen oxides, ammonia, and other harmful contaminants. It can also be used to measure inorganic arsenic in water samples. 

· · Advantages

GPCL is a highly sensitive, rapid, and facile method that produces output without background luminescence. 

Here are some examples of GPCL applications: 

Measuring nitric oxide in aqueous solutions

A gas-phase microdialysis-chemiluminescence method uses a helium dialysate to extract volatile analytes into the gas phase. 

· · Measuring inorganic arsenic in water samples

A GPCL technique uses internal hydrogen pressure to transfer arsine into a chemiluminescence reaction cell. 

· · Measuring tin

A GPCL technique uses ozone to oxidize stannane, which produces chemiluminescence that can be used to measure tin

Beta ray attenuation

Beta ray attenuation is a technique that measures the amount of material present by measuring the attenuation of beta rays as they pass through it: 

How it works

Beta rays are high-speed electrons that are emitted when unstable atomic nuclei decay. When beta rays pass through a substance, they collide with the atoms, causing ionization and excitation. This results in the attenuation of the beta rays, which is proportional to the mass of the substance. 

· · Uses

Beta ray attenuation is used in a variety of applications, including: 

Measuring particulate matter: Beta attenuation is used to measure the concentration of particulate matter in the air. A beta radiation source emits beta particles that pass through an air sample, and a detector measures the intensity of the remaining beta particles. This measurement is used to calculate the concentration of particulate matter. 

· · Measuring the thickness or weight of materials: Beta ray attenuation is used to determine the thickness or weight of materials like plastics, metals, and paper. 

· · Estimating water content: Beta ray attenuation can be used to estimate the water content of wheat. 

Beta ray attenuation is the most widely used real-time technique for monitoring ambient air quality. However, some have reported shortcomings in the technique that can lead to compromised data quality.

Energy Dispersive X-ray Fluorescence (EDXRF)

Energy Dispersive X-ray Fluorescence (EDXRF) is a non-destructive analytical technique that identifies and measures the elemental composition of materials. It's used in many industries, including: 

Manufacturing: For quality and process control in the production of metals, chemicals, polymers, glass, and cement 

· Environmental testing: For pollution monitoring of solid waste, effluent, and cleaning fluids 

· Food safety: For analyzing foodstuffs and cosmetics 

· Pharmaceuticals: For analyzing pharmaceutical products 

· Forensics: For analyzing samples in forensic investigations

EDXRF works by: 

Separating X-rays: Separating the characteristic X-rays of different elements into a fluorescence energy spectrum 

· Measuring X-rays: Measuring the different energies of the emitted X-rays from the sample 

· Generating a spectrum: Counting and plotting the relative numbers of X-rays at each energy to generate an XRF spectrum 

· Analyzing the spectrum: Processing the spectrum for qualitative or quantitative analysis 

EDXRF is suitable for almost all sample types, and requires little to no sample preparation. It's also capable of analyzing a wide range of atomic elements, from sodium through uranium.

Non-dispersive infrared (NDIR)

Non-dispersive infrared (NDIR) spectroscopy is a method for measuring the concentration of gases by analyzing the infrared light they absorb: 

How it works

An infrared beam passes through a sample chamber, and each gas absorbs a specific frequency of infrared light. The amount of absorbed infrared light at the relevant frequency is measured to determine the gas concentration. 

· Why it's called non-dispersive

NDIR spectroscopy is called non-dispersive because it doesn't use a dispersive element, like a prism or diffraction grating, to pre-filter the wavelength that passes through the sample chamber. Instead, an optical filter is placed in front of the detector to eliminate all light except for the wavelength that the selected gas molecules can absorb. 

· What it's used for

NDIR spectroscopy is often used to detect and measure the concentration of gases like carbon monoxide, carbon dioxide, nitrogen dioxide, and sulfur dioxide. These gases can be lethal or explosive in high concentrations, so monitoring them is important in certain environments. 

· Applications

NDIR spectroscopy is used in a variety of applications, including oil and gas, renewable energy, and hydrogen. 

Gas chromatography (GC

Gas chromatography (GC) is a technique used to separate and analyze the components of a mixture: 

How it works

A liquid or gaseous sample is injected into a carrier gas, which is usually an inert gas like helium, argon, nitrogen, or hydrogen. The carrier gas moves the sample through a separation column, which contains a stationary phase that can be solid or liquid. The components of the sample separate inside the column, and a detector measures the amount of each component that exits. 

· What it's used for

GC is used in many areas, including industrial analysis, food and aroma analysis, environmental analysis, and forensic investigations. Some examples of GC applications include detecting toxic compounds, narcotics, and medicaments in biological fluids. 

· What to consider

The compounds being analyzed must be stable under GC conditions, have a vapor pressure greater than zero, and be less than 1,000 Da. The sample must also be salt-free and free of ions.

Atomic absorption spectrometry (AAS) and inductively coupled plasma (ICP)

Atomic absorption spectrometry (AAS) and inductively coupled plasma (ICP) are both analytical techniques used to determine the elemental composition of samples. They are used in a variety of fields, including environmental monitoring, materials science, and pharmaceuticals. 

The main difference between AAS and ICP is that ICP measures multiple elements at once, while AAS measures one or a few elements at a time. Other differences include: 

Temperature: ICP-OES uses a high-temperature argon plasma to break down a sample, while AAS flames don't exceed 3000° C.

· Cost: AAS is generally less expensive than ICP-OES. 

· Ease of use: AAS is relatively simple to run and maintain. 

· Detection limits: ICP-OES has lower detection limits than AAS. 

Here's how AAS works:

A sample is aspirated into a flame.

A radiation source is directed at the sample.

The change in radiation intensity after it passes through the sample is measured.

High-performance liquid chromatography (HPLC)

High-performance liquid chromatography (HPLC) is an analytical technique that separates compounds in a chemical mixture. Here are some things to know about HPLC: 

How it works

A liquid sample is injected into a solvent stream that flows through a column packed with a separation medium. The sample components separate as they flow through the column. 

· What it can do

HPLC can identify compounds, determine how much of each compound is in a mixture, and purify molecules. It can be used to analyze a wide range of organic compounds, including non-volatile or thermally unstable molecules. 

· How it's used

HPLC is often used to diagnose anemia, sickle cell disease, and other hemoglobin abnormalities. It can also be used to identify organic compounds synthesized in a lab. 

· Advantages

HPLC is versatile, sensitive, and can be applied to complex mixtures. It can also be used as a non-destructive technique, allowing samples to be recovered if needed. 

· Limitations

Quantification can be slow, and the instrument can require large volumes of solvents. 

· Column temperature

Column temperature can significantly influence the separation, so it's important to maintain consistent conditions. 

· Pump pressure

Modern HPLC systems can work at higher pressures, allowing for smaller particle sizes in the columns. 

· Automation

Most HPLCs are now fully automated and controlled by computer.