The ozone we breathe in Albacete.

In March of this year we had the opportunity to perform a first look at air quality in Albacete, our city, talking about the evolution of particles in recent years, all thanks to a reference that appeared in the written press that we thought needed to be clarified at the time.

After clarifying the concept of particle pollution and seeing its evolution in the last decade, using data mining tools, we are going to analyze this time another pollutant that tends to become very fashionable in summer and that appears every so often in the press. We are talking about Ozone.

The Ozone we breathe.

The oldest of us still remember how in the 80s what perhaps was came to light The first global environmental problem of true media reach: The hole in the ozone layer.

As this environmental problem clearly had an impact on our health, the tools for its resolution appeared relatively soon, and in 1987 a large group of countries signed the well-known Montreal Protocol, banning the use of harmful CFCs (chlorofluorocarbons) that used up ozone. Three decades later, the problem seems to be starting to subside and The hole observed in Antarctica is beginning to show an effective reduction in its surface at their lowest detection levels.

However, this environmental problem made it friendly to Ozone, a Molecule composed of three oxygens That, although In the upper layers it protects us of the Sun's dangerous ultraviolet radiation, when it is found In the air we breathe (what we technicians call the troposphere), becomes a contaminant especially relevant also because of its high oxidizing capacity.

In fact, ozone in the air we breathe It can affect the mucous membranes, causing irritation or even aggravating respiratory ailments, to the tissues of living beings, and even to construction materials of our cities, when their exposure to high concentrations is prolonged over time.

Looking for the culprit of the crime.

No one, or rather, almost no one, deliberately emits ozone into the atmosphere (this is not the time to talk about ozone generators for disinfection).

Ozone is a secondary pollutant, and is generated in situations where there are adequate weather conditions for certain primary pollutants or precursors, already present in the air, to react and generate it in its decomposition.

It can also be generated by the ionization given in the air in a lightning storm, or even by the exchange of flows between the stratosphere and the troposphere, in very specific disturbances, although both cases are exceptional and hardly cause the ozone that afflicts us as a pollutant in our daily lives.

In most cities, nitrogen oxides (NOx) are the precursors. This same pollutant, which is generated by man and is therefore referred to as primary, is at the same time responsible for the destruction of ozone, generating cross-reactions that allow its destruction, presenting a behavior similar to a “chemical buffer”.

NO₂ + hv → NO + O

O + O₂ → OR₃

O₃ + NO → NO₂ + OR₂

In certain places, with a significant degree of traffic pollution, or under the influence of certain industrial activities, Ozone can also come from other precursors such as volatile organic compounds (VOCs).

And in Albacete, when do we have Ozone?

In cities with an average concentration of primary pollutants, such as The case of Albacete, Ozone is mainly produced by the influence of weather conditions and in particular because of the existence of a high temperature, low humidity and high solar radiation.

In this way, as shown in the following graph, if we study the temporal variation of Ozone in Albacete over the last decade, we can verify that the obtained averages present the following casuistics:

• They reach Its maximum at the middle of the day.

Why? — Because this is when more solar radiation is recorded and the highest temperatures are reached, between 12:00 and 18:00.

• At peak NOx generation, first thing in the morning, is when they are reached The Ozone minimums.

Why? — Because existing ozone, in the absence of solar radiation to generate it, reacts with primary pollutants produced by man, resulting from road traffic emissions recorded during the week, decomposing.

• Baseline levels (minimum values), registered On the weekend, They are higher than those registered during the week.

Why? — Because on the weekend there are no relevant primary broadcasts, which in Albacete come mainly from traffic. In this way, since ozone lacks a sufficient concentration of primaries that generate it, but that also deplete it, it has the highest lows of the entire week.

• Los Main summer months, and mainly June and July, is when they occur The highest average ozone levels.

Why? — Because that's when the weather conditions that we mentioned at the beginning at their peak are combined: high temperature, low humidity and high solar radiation.

And in Albacete, how does Ozone evolve?

If we look for a trend for ozone in the last decade, once the data have been seasonally adjusted (with the fluctuations due to the weather conditions that occur at each time of the year, which affect ozone so much), we can observe that Ozone shows a gradual increase in its average concentrations Which year over year translates into an average increase of 0.99 µg/m³ per year.

However, this trend of increasing levels seems to be increasing related to the evolution of weather conditions than with a parallel increase in the number of precursors. In fact, if we analyze the trend for NO2, this primary pollutant of anthropogenic origin seems to have experienced a decrease in its average concentrations that is practically equivalent to that experienced by ozone, with levels of -9.92 µg/m³ per year.

What he also seems to have presented a negative evolution, as we already observed in the past for particle data, is the quality of the Ozone data.

Over the years 2013 and 2014 The loss of data in ozone equipment causes the volume of valid data do not exceed the percentages of 60.6% and 75.2%, respectively, still at 88.7% in 2015, despite the changes made to the network.

These values are well below what is usually acceptable for a control network, and even the values of previous years (for example, during 2012 ozone was 93% of valid data), even jeopardizing the validity of the equipment for determining air quality.