The WHO air quality standards were renewed in September 2021. The largest decrease (75%) targeted the annual value of nitrogen dioxide (NO2). Despite the severity of the new guidelines, economic studies that estimate the impact of nitrogen dioxide (NO2) are lacking. The present study aims to start filling this gap by estimating the impact of the daily concentration of nitrogen dioxide (NO2) on the number of hospital admissions due to respiratory-related reasons in Portugal between January 1, 2016, and December 31, 2018. I find that a 1 microg/m3 increase in daily nitrogen dioxide (NO2) concentration leads to a 2.6% increase in the number of hospital admissions due to specific respiratory-related reasons (pneumonia, chronic obstructive pulmonary disease (COPD), asthma) among the children 2 – 5 years old. When considering the group of the most polluted parishes in the country, the magnitude of the impact increases to 3.3%, suggesting a non-linear relationship between exposure and the impact. A back-of-the-envelope estimate of the costs of a 1 microg/m3 increase in daily NO2 concentration is between 260 and 830 thousand euros (2018). In Portugal, the richer, younger, and more educated part of the population is exposed to higher-than-average daily NO2 concentrations. I propose Low Emission Zones as an efficient policy to decrease ambient nitrogen dioxide levels in Portugal. (JMP)
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