**4. Conclusion**

The seasonal cycles obtained for formaldehyde, acetaldehyde, and acetone-acrolein with respect to the other carbonyls suggest different formation mechanism and sinks compared to the others. This could be due to photochemical processes (oxidation of biogenic and even anthropogenic hydrocarbons that arrive to the area under determined meteorological condi‐ tions) and also the direct emission from vegetation. For example, two Mediterranean tree species such as *Quercus ilex* (holm oak), one of the most abundant oak in the study area, and

The formaldehyde and acetaldehyde concentrations measured at Cabañeros National Park are in the same range or lower than the levels reported in other forests or rural areas (Germany [56] and Brazil [57]). Our data are similar to those reported in the small village of Covelo in

On the other hand, the levels found in the ecological area during the months of February and March for formaldehyde (0.51 and 0.59 µg m-3) and acetaldehyde (0.33 and 0.29 µg m-3) are lower than those registered in the urban (outdoor samples collected at the same time as common areas of Faculty of Chemistry or University Library) and industrial area (outdoor samples collected in the school) during the same period. Also, the levels of both aldehydes during the months of May and June were lower (1.15-1.37 µg m-3 for formaldehyde and 0.70-1.09 µg m-3 for acetaldehyde) than the levels registered in the industrial area during the

Formaldehyde is classified in Group 1 by IARC. It was based on inhalation causing squamous cell carcinoma in rats and nasopharyngeal cancer in humans [3]. Recently, the classification has been expanded with formaldehyde causing leukemia and limited evidence of sinonasal cancer in humans [59]. The lowest concentration reported to cause sensory irritation of the eyes in humans is 0.38 mg m-3 for 4 h. Increases in eye blink frequency and conjunctival redness appear at 0.6 mg m-3, which is considered equal to the no-observed-adverse-effect level (NOAEL). There is no indication of accumulation of effects over time with prolonged exposure, and there is no evidence indicating an increased sensitivity to sensory irritation to formalde‐ hyde among people often regarded as susceptible (asthmatics, children, and older people) [60]. The formaldehyde exposure-response relationship is highly nonlinear and biphasic, support‐ ing a NOAEL that allows setting a guideline value [60]. This means that it cannot be assumed a low-dose linear relationship for the carcinogenic effects, and therefore, the calculation of the incremental lifetime risk of cancer for formaldehyde, assuming a low-dose linear relationship,

As commented above, WHO established a guideline value for formaldehyde of 100 µg m-3 that should not be exceeded for any 30-min period of the day [47]. This short-term guideline will also prevent effects on lung function as well as long-term health effects, including nasophar‐

We can compare our data with the short-term guideline value of 100 µg m-3. In our study, the maximum values registered in the different environments were below 100 µg m-3, except for

*Pinus pea* (Italian stone pine) emit formaldehyde and acetaldehyde [54, 55].

Portugal, considered as a rural/forest site [58].

**3.3. Health risk evaluation**

78 Current Air Quality Issues

same months in the outdoor samples collected in the homes.

would give a value highly overestimated and it would be meaningless.

yngeal cancer and myeloid leukemia [60].

This paper presents an overview of the concentrations of priority aldehydes observed in indoor and outdoor air in an urban and an industrial area of central-southern Spain. Very few studies have been carried out in the indoor air of Spain. Therefore, we have tried to gather the data previously published about formaldehyde and acetaldehyde in this region and other new data to obtain a general view of the levels in different outdoor and indoor environments.

From the results, we can conclude that the highest concentrations of formaldehyde and acetaldehyde are found inside the homes and schools. The levels of formaldehyde in labora‐ tories or in rooms near laboratories, where many kinds of solvents are used, are much lower. Overall indoor and outdoor concentrations of formaldehyde and acetaldehyde in all sites sampled were below the threshold limit of 100 µg m-3 proposed by WHO [47] associated with nose and throat irritation and also to prevent all types of cancer. Therefore, it represents the recommended maximal value. In our study, there is no such place with formaldehyde values exceeding this level. Despite that, it is important to note that the sampling period was 14 and 7 days for Analyst® and Radiello®, respectively. Thus our results express an average concen‐ tration over a long period and do not provide information about exposure peaks, which must be much higher than the average concentration measured. On the other hand, the indoor formaldehyde concentrations in the homes and one school monitored exceeded the recom‐ mended guideline value of 30 µg m-3 proposed by Kotzias et al. [48] for the prevention of irritant effects. Also this value is referred to a period of 30 min.

Therefore, although the indoor sources are dominant for all sites sampled, the most important to be studied are at homes and schools. This is only a preliminary study about the levels of formaldehyde and acetaldehyde in homes and schools due to the low number of samples, and an exhaustive research is necessary in order to better characterize the chemical composition of the air that people breathe daily and to assess the health risk.
