Many of my customers know that when purchasing air filters to filter particulate matter, there are many standards to refer to, such as EN779, EN1822, MERV, ISO16890, etc. However, the relevant standards are often unclear when purchasing air filters for filtering gas.
Currently commonly used standards for gas filtration include automotive cabin filtration (ISO 11155-2, etc.), HVAC filter materials, and filters (ISO 10121-1, 10121-2, etc.).
In this article, I will discuss what standards you can refer to when filtering chemical gases.
Chemical gas pollutants
In addition to suspended particulate matter in the air, there is also a type of harmful substances – chemical gases, which are often invisible and intangible but often more harmful. They exist as gas molecules, which cannot be removed by ordinary air filters but require molecular-level adsorption, such as activated carbon, molecular sieve porous media, etc.
These gases mainly include organic compounds (VOC, including toluene, acetone, etc.), acidic gases (such as SO2, H2S, etc.), alkaline gases (such as NH3), and other gases (such as CO).
Gases of different properties are harmful to different degrees and, therefore, have different allowable limits.
Generally, porous media such as activated carbon are often made into filters, and adsorption devices process the incoming air to adsorb or remove these gaseous pollutants. Such as activated carbon filters, etc.,
So, what is the filter’s adsorption and removal rate of these gases, and what method is used to test and evaluate it? Some standards have made relevant provisions.
Summary of standards
There are three main types of filters for automobile air conditioners: general ventilation and gas masks, which will involve the use and requirements of the above chemical gas filtration.
Because my product is air filters, so I will not discuss gas masks too much here.
Car cabin air filter
There are currently three relevant standards for activated carbon automotive cabin air filters.
| Item | Standard | Region |
| 1 | ISO11155-2 Road vehicle-Air filters for passenger compartments-Part2:Test for gaseous filtration. | International |
| 2 | GB/T 32085.2 Car cabin air filter Part 2: Test for gaseous filtration. | China |
| 3 | DIN 71460-2 Road vehicle for passenger compartments -Part 2: Test for gaseous filtration. | Germany |
General ventilation Air filter
There are 5 standards for gas-phase air filter materials and filters for general ventilation.
| Item | Standard | Region |
| 1 | ISO 10121-1 Test method for assessing the performance of gas-phase air cleaning media and devices for general ventilation – Part 1: gas-phase air cleaning media. | International |
| 2 | ISO 10121-2 Test method for assessing the performance of gas-phase air cleaning media and devices for general ventilation – Part 2: gas-phase air cleaning media. | International |
| 3 | JIS B 9001:1977 Gas-removal — method of test for performance of gas-removal filters. | Japan |
| 4 | ANSI/ASHRAE 145.2 Laboratory Test Method for Assessing the Performance of Gas-phase Air-cleaning Systems: Air-cleaning Devices. | USA |
| 5 | ASTM D 5160-95 Standard Guide for gas phase adsorption testing of activated carbon. | USA |
Test indicators
The automotive cabin air filter is specially used for air purification in automobile cabins. HVAC gas phase air filter materials and filters for general ventilation are aimed at commercial buildings and general factories that do not produce toxic and harmful substances.
In practice, activated carbon composite filter cloth composed of activated carbon and filament non-woven fabric, commonly known as sandwich carbon cloth, is generally used to make filters of various shapes.
Gas filter test indicators
Regarding the adsorption performance of gaseous pollutants of activated carbon filters, the test indicators include:
- Airflow resistance (flow-pressure drop curve).
- Adsorption efficiency (removal efficiency).
- Dirt holding capacity.
- Desorption characteristics (retention force).
The dirt-holding capacity refers to the total amount of gaseous pollutants adsorbed by the filter during the test period.
Will the adsorbed gas be released again? This is desorption, which is defined as “the release of previously trapped contaminants from the test filter”;
Retention is defined as “a measure of the ability of an adsorbent or filter to resist desorption.” Therefore, a good gas filter material not only has higher gas removal efficiency but also has good retention power.
Evaluation method
Regarding the test of gas desorption performance, the test and evaluation method specified for automotive cabin filters is to monitor the changes in downstream gas concentration after the injection of chemical gas pollutants stops.
The general ventilation filter standard is called retention force, and the prescribed method is to use zero-concentration gas loading to evaluate the desorption characteristics.
The evaluation of filter materials is very important for the actual use effect of subsequent filter products. Only under suitable conditions can high-quality products be obtained when good filter materials are selected and supplemented by good manufacturing processes.
Gas type and concentration
The types and concentrations of gases are clearly stated while testing different air filters specified in each standard.
For cabin air filter
In the gas filtration test of vehicle cabin filters, the gas types and concentration settings specified by international, German, and Chinese standards are the same. See the table below for details.
| Contaminants for testing | Concentration set value | Explanation |
| n-butane | 80 ppm | ISO11155-2, GB/T 32085.2, DIN 71460-2 stipulates that n-butane and toluene must be used, and sulfur dioxide is optional. |
| Toluene | 80 ppm | ISO11155-2, GB/T 32085.2, DIN 71460-2 stipulates that n-butane and toluene must be used, and sulfur dioxide is optional. |
| SO2 | 30 ppm | ISO11155-2, GB/T 32085.2, DIN 71460-2 stipulates that n-butane and toluene must be used, and sulfur dioxide is optional. |
| NOx | 30 ppm | DIN 71460-2 stipulates selection. |
The mandatory pollutants are n-butane and toluene; the optional pollutant is SO2.
The difference is that the available gases in the German standard include more NOX, and the concentration is 30 ppm.
For air filters for general ventilation
The types and concentrations of test gases stipulated in various national standards are different for gas-phase air filter materials and filters used for general ventilation.
I have listed several gases and concentrations each standard recommends in the table below. The types of gases involved in some standards are not fully listed. It is recommended to check the corresponding standards for your products’ compliance.
| Contaminants for testing | ISO 10121-1 Filter material | ISO 10121-2 Air filter efficiency test | ISO 10121-2 Air filter dirt holding test | JIS B9901 Air filter efficiency test | JIS B9901 Air filter dirt holding test | ASHRAE 145.2 Air filter |
| Acidic SO2 | 9 or 90 ppm | 450 ppb | 9 or 90 ppm | 0.5 ppm | 20 ppm | 50 ppb-35 ppm |
| Alkaline NH3 | 9 or 90 ppm | 450 ppb | 9 or 90 ppm | 10 ppm | 100 ppm | 100 ppb – 75 ppm |
| Voc toluene | 9 or 90 ppm | 450 ppb | 9 or 90 ppm | 3 ppm | 1000 ppm | 400 ppb – 50 ppm |
Findings
We can see from the provisions of various standards that the gas concentration used in the efficiency test is usually smaller than that used in the dirt holding capacity test.
In actual use, the gas concentration is much lower than that specified in the standard. Using low concentrations to test filtration efficiency can improve the accuracy of the test results.
For example, when testing with toluene at high concentrations, due to the small volume of activated carbon pores, there will be situations such as easy desorption that do not exist in actual use, and the isotherm ordering of different adsorbents can also change.
Moreover, the materials proposed in the standard that perform best in high-concentration tests may not necessarily be the best in low concentrations or actual use.
The dirt-holding capacity test uses a high concentration, which can be compared to the dust-holding capacity of a filter. A large concentration can shorten the test time. Otherwise, completing the test at a low concentration may take days or months.
In the above two major categories of standards, whether filter material testing, filter testing, efficiency testing, or pollution capacity testing, the specified gas concentrations are mostly between 50 ppb and 100 ppm.
Only a few substances, such as CO and toluene, in Japan’s JIS B9901 have a concentration of 1000ppm in the pollution capacity test.
My summary
The application fields of chemical gas filtration include automobile cabin filtration, HVAC filtration, etc. Car cabin filtration and HVAC filter test indicators include resistance, dirt-holding capacity, removal efficiency, and retention (desorption characteristics).
Various gases are required to test gas filter materials and air filters. Commonly used are acidic gases, represented by SO2; alkaline gases, represented by NH3; and VOC gases, represented by toluene. In addition, there are n-butane, H2S, NOX, CO, etc.
Regulations on gas concentration:
The recommended gas concentrations for automotive cabin filtration (ISO 11155-2, etc.), HVAC filter materials, and filters (ISO 10121-1, 10121-2, etc.) are between 50 ppb and 100 ppm.
Only the Japanese JIS B9901 standard requires the concentration of CO and toluene to be 1000ppm during the pollution capacity test. I think using 100 ppm gas can meet the needs during testing, and there is no need to increase test risks in pursuit of high concentrations.
