From February 2011 to September 2012, PM 1 samples were collected at the regional background station of Mt. Aitana, located near the eastern coast of the Iberian Peninsula at 1558 m a.s.l. Samples were subsequently analyzed to determine the major chemical composition (elemental and organic carbon, secondary inorganic ions and oxalate). The seasonal patterns of the concentrations of PM 1 and its main components and the influence of long-range transport of dust from the Sahara desert were studied in this work. PM 1 was mainly composed of organic matter and ammonium sulfate, while EC and nitrate were minor components. Concentrations ranged from 3.4 µg m -3 in winter to 5.8 µg m -3 during summer. This seasonal cycle is typical of high mountain sites, which are generally above the planetary boundary layer during winter time. All the analyzed components exhibited the same seasonal pattern except nitrate, which showed minimum values in summer. This is most likely the result of the decomposition of NH 4 NO 3 favored by the higher summer temperatures. Due to the close proximity to the African continent, PM 1 levels significantly increased during Saharan dust intrusions. The concentrations of sulfate were 35% higher during dust events since the formation of secondary ammonium sulfate is favored by heterogeneous reactions on the surface of mineral particles.

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From May to September 2012, ozone reductions associated with 15 Saharan dust outbreaks which occurred between May to September 2012 have been evaluated. The campaign was performed at a mountain station located near the eastern coast of the Iberian Peninsula. The study has two main goals: firstly, to analyze the decreasing gradient of ozone concentration during the course of the Saharan episodes. These gradients vary from 0.2 to 0.6 ppb h(-1) with an average value of 0.39 ppb h(-1). The negative correlation between ozone and coarse particles occurs almost simultaneously. Moreover, although the concentration of coarse particles remained high throughout the episode, the time series shows the saturation of the ozone loss. The highest ozone depletion has been obtained during the last hours of the day, from 18:00 to 23:00 UTC. Outbreaks registered during this campaign have been more intense in this time slot. The second objective is to establish from which coarse particle concentration a significant ozone depletion can be observed and to quantify this reduction. In this regard, it has been confirmed that when the hourly particle concentration recorded during the Saharan dust outbreaks is above the hourly particle median values (N > N-median), the ozone concentration reduction obtained is statistically significant. An average ozone reduction of 5.5 % during Saharan events has been recorded. In certain cases, this percentage can reach values of higher than 15 %.

In early 2020, the COVID-19 pandemic spread globally, and severe measures to control it were implemented. This study investigates the impact of the lockdown on the air quality of three provinces in the Valencia region, eastern Spain, in the years 2015–2020, focusing on particulate matter (PM). A thorough statistical analysis using different approaches is conducted. Hourly patterns are also assessed. In addition, the role of meteorological parameters on PM is explored. The results indicate an overall PM10 reduction of 16.5% when comparing the lockdown in 2020 and the 2015–2019 period, while PM2.5 increased by 3.1%. As expected, urban zones experienced higher reductions than suburban zones, which experienced a PM concentration increase. The impact of the drastic drops of benzene, toluene and xylene (77.4%, 58.0% and 61.8%, respectively) on the PM values observed in urban sites is discussed. Our study provides insights on the effect of activity changes over a wide region covering a variety of air quality stations, urban, suburban and rural, and different emission types. The results of this work are a valuable reference and suggest the need for considering different factors when establishing scientific air pollution control strategies.

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