The “Photochemistry, atmospheric chemistry, and air quality” research group (FOTOAIR), of the Department of Physical Chemistry of the University of Castilla-La Mancha, investigates the atmospheric degradation processes of volatile organic compounds (VOCs) initiated by OH, Cl, and O3 and the formation mechanism of products, such as O3 and secondary organic aerosols, which affect the quality of the outdoor air. Therefore, the quality of the air we breathe both indoors and outdoors has to be evaluated to see its impact through the formation of secondary pollutants and if they can contribute to increasing atmospheric concentrations that affect the human health.


Atmospheric pollution.

The chemistry of the troposphere, the layer of the atmosphere where we breathe, governs the pollution processes that directly or indirectly affect our health. Due to its proximity to the Earth’s surface, the troposphere emits, both naturally and due to human activity, a large amount of pollutant. In the presence of high concentrations of NOx and sunlight, these pollutants produce the so-called photochemical smog at a local scale (rural or urban). The atmospheric degradation of primary pollutants generates others such as ozone (O3), formaldehyde (HCHO) or particles. The effect of air pollution can also be suffered hundreds of kilometers from the source of emission of the primary pollutant due to the atmospheric transport which can cause the formation of secondary pollutants far away O3 (regional scale). All this is detailed in the research line “Atmospheric Chemistry

Concerning the atmospheric particles, the main source of emission comes from the combustion engines, domestic heating, or the biomass burning. Fine particles are classified according to their size: PM1,0, PM2,5 or PM10, with aerodynamic diameters of less than 1, 2.5 and 10 µm (1 micron (µm) = 0.001 mm), respectively. Within the fine particles, ultrafine particles (PM0,1) are those with diameters smaller than 0.1 µm. PM10 particles correspond to the entire diameter range of fine and ultrafine particles and constitute the so-called ‘inhalable particles’. The fine and ultrafine particles enter the respiratory system, being able to reach the pulmonary alveoli. These particles have a diameter much smaller than that of a human hair or a fine grain of sand.

Other ultrafine particles, such as the secondary organic aerosols (SOAs), are formed in situ in the atmosphere as a consequence of photochemical reactions of VOCs with atmospheric oxidants, such as the hydroxyl radical (OH), chlorine atoms (Cl) or ozone.



Comparative size of the fine and ultrafine particles that are inhaled and reach the deepest parts of the lungs.


Indoor air quality

We spend much of our time indoors (workplaces, classrooms, home, transportation, etc.). We must not forget that in these spaces the air can be full of polluting gases. The main indoor pollutants are CO, NO2, formaldehyde, benzene, and particles. Given that in developed countries we spend around 85% of our time indoors, it is important to control the air quality in these environments.

We all remember that many years ago the use of fire pits in rural homes was the source of heating together with fireplaces. The incomplete combustion of these braziers emitted CO that caused, in the best of cases, headaches or, in the worst of cases, death from poisoning. Currently, CO is generated from the incomplete combustion of fuels such as natural gas, charcoal, gasoline, and tobacco.

One of the main pollutants that is generally found in higher concentrations in indoor air than in outdoor air is formaldehyde. In addition to being caused by cigarettes and other tobacco products, gas stoves, and fireplaces open to the air, it is found in many products that are used daily at home. For example, disinfectants, cleaning products, glues, and adhesives or varnishes. Another example of an indoor pollutant is benzene. Burning incense or using heating without ventilation or cooking with kerosene stoves can raise benzene levels indoors.

Factors such as poor ventilation, cleaning conditions and products, building characteristics, cultural habits, climate, and the outdoor environment do influence indoor air quality.

Recently, hydroxyl radicals (OH) have been detected indoors at similar concentrations to the atmospheric ones. The reactivity of OH with indoor pollutants can give rise to other secondary pollutants. One of the pollutants found in indoor air is phthalates, which are used mainly as PVC plasticizers, adhesives, kitchenware, food packaging, etc. Since there is no chemical bond between the phthalate and the plastic which is mixed with, these compounds are very easily released into the air. However, despite its widespread use, there is no information about its reactivity in the gas phase.


Real-time monitoring of contaminants in indoor environments

CO2 measurement to control the quality of ventilation and reduce the risk of aerosol transmission of SARs-CoV-2

In these 2 years of the SARs-CoV-2 pandemic, much has been said about the routes of transmission of the virus. The main route of infection is airborne, specifically, by aerosols. Measuring the ambient CO2 in an indoor space is a simple and inexpensive way to evaluate the quality of ventilation. When we breathe, we exhale CO2 and bioaerosols that, in an infected person with COVID-19, would contain the virus. In addition, the indoor levels of CO2 give an idea of the amount of “second-hand” air breathed which may contain virus-infected aerosols (Table 1). The ambient concentration of CO2 is usually expressed as a mixing ratio in parts per million in volume (ppmv o simply ppm), that is, the number of CO2 molecules per million air molecules in a certain volume.


Table 1. Percentage of air breathed with respect to the CO2 indoor concentration (

CO2 indoor level

CO2 int / ppm

< 500150<0,33
< 700300<0,71

CO2 exterior ≈ 420 ppm; ΔCO2 = CO2 ext – CO2 int


Measurement of volatile organic compounds (VOCs) and ultrafine particles in indoor air

A Proton Transfer Time-of-Flight Mass Spectrometer (PTR-ToF-MS) is used to detect and identify gaseous pollutants in indoor air. The detection of ultrafine particles and their size distribution between 5.6 nm and 560 nm is carried out using a Fast mobility Particle Sizer (FPMS) spectrometer.