ADVANCEMENT OF THE SCIENCE
When we considered the time of exceed- ance in the analysis, it was evident that PM levels are higher when measured at street level than at rooftop height. This finding is relevant because the information available for environmental pollutants is provided mainly from monitoring stations placed on building roofs. According to our data, these measures underestimate real exposure at the street level. The eect of pollutants on respiratory health measured through CO-oximetry or %COHb was not evident. On average, CO- oximetry after the cycling trips was lower than before. A possible explanation is that an increase in ventilation during physical eort caused by cycling, in a short period, might wash pollutants from the respiratory airway, thus resulting in reduced exhaled CO after the cycling trip. Cavaliere et al. (2009) demonstrated in healthy voluntary participants that exhaled CO decreased during acute hyperventila- tion (10%) but to a much lesser extent than exhaled CO 2 (25%). Similarly, Cope et al. (2004) found that ventilation patterns strongly influence the quantification of volatile analytes in exhaled breath, and observed a reduction of CO exhaled levels during hyperventilation. The balance between the health benefits of physical activity (i.e., active transport in our study) and health risks due to exposure to pol- lutants (e.g., PM 2.5 , PM 10 , NO 2 ) has been studied by several authors. Tainio et al. (2016) defined a model that included air pollution exposures due to active travel and estimated the dier- ences in the inhaled dose of fine particulate matter (PM 2.5 ), time of cycling, and risk for all- cause mortality. The break-even point beyond which additional physical activity might cause an increased risk for all-cause mortality was 300 min of cycling per day. Cycling trips in our experiment did not last >60 min, and they were defined according to the routes usually taken by active transport users. Tainio et al. (2021) performed a mapping review of empirical and modeling evidence to identify possible links between exposure to air pollution and physical activity. Obser- vational epidemiological studies identified in the review provided some evidence for a pos- sible interaction between air pollution and physical activity for acute health outcomes in environments with high concentrations of pollutants (most studies were done in Europe
or North America). They also reported that public health modeling studies have esti- mated that, in most situations, the benefits of physical activity outweigh the risks of air pol- lution—at least in the active transport envi- ronment. Evidence was scarce, however, for low- and middle-income countries. In our study, we found low levels of NO 2 in routes that included busy streets within a city. Therefore, for cyclists in Montevideo, we find it reasonable to assume that the benefits of active transport likely outweigh the risks. The impact of noise on human health depends on several factors, including the level of noise, the person who is exposed, and the exposure duration. In our study, noise has been one of the highest pollutants in the stud- ied routes. We found that in 21 days, cyclists were exposed to >70 dBA more than 70% of the duration of the cycling trips. Guidelines for European countries rec- ommend reducing trac noise levels to <53 dBA/day (WHO, 2019). Noise is an impor- tant stressor and contributes to increased risk of hypertension. Hypertension is one of the major risk factors for chronic disease in Uruguay (Hammer et al., 2014; Ministry of Public Health, 2018). As Gelb and Appari- cio (2021) note, active transport users are exposed to a situation of clear injustice, as they are more exposed than other road users to environmental pollution—pollution that they do not contribute to producing them- selves. They also found that cyclist exposure to noise is more dependent on the charac- teristics of the microscale environment (i.e., environments studied at the microscale, usually at characteristic distances not >300 m). This finding makes it possible to mod- ify noise exposure by choosing appropriate streets to place active transport ways. In our study, this component should be balanced with trac levels. One strength of our study was that we mea- sured air pollution at street level in a habitual active transport route and compared street- level measurements with roof-level air quality monitoring. This relationship had not been studied in Montevideo. Study routes were defined by experienced active transport users and thus represent routes that are the most used to access work for part of the population. Regarding limitations, the accuracy of mea- sures, mainly CO, could be skewed due to hyperventilation. Some of the measures were
performed right after the COVID-19 mitiga- tion control measures were suspended, and thus the trac burden could be underrep- resented during part of the data collection period. This fact constitutes a limitation of our study, although we did not conduct measure- ments during pandemic lockdown periods. Nevertheless, sound pressure levels were also higher during days with less trac flow. Furthermore, our study did not include other risks related to trac routes such as acci- dents, which could represent extra health burdens for active transport users. As we have shown, the usual air quality monitoring conducted in Montevideo is at roof level, and as such is not an accurate measure of air pollution at the street level. Future research to have a better representation of modeling data obtained in roof-level monitoring stations could be useful for health prevention pur- poses. Moreover, adding data of other deter- minants of street-level pollution to predict real exposure to cyclists of health-threatening air pollutants would benefit both cyclists and the broader public by informing mitigation strate- gies to lower atmospheric pollution. Conclusion Even though the street level of pollutants is above recommended thresholds, active trans- port benefits seem to outweigh health risks in Montevideo in our study on routes usually used by cyclists. Our study provided some knowl- edge about characteristics of the environment to be considered by city planners when select- ing where to place bikeways in Montevideo. According to the Intergovernmental Net- work on Air Pollution for Latin America and the Caribbean (2022), approximately 7 million people die every year around the world due to diseases and infections related to indoor and outdoor air pollution. In addition, Willberg et al. (2023) concluded that air pollution results in 400,000 premature deaths in Europe every year. In Uruguay, according to the Climate and Clean Air Coalition (2022), there are approxi- mately 250 premature deaths every year related to outdoor exposure to PM 2.5 . Consequently, air pollution research is a key aspect in guiding environmental public health practice. In this study, we conducted a mobile moni- toring of personal exposure to air pollutants. This technique allows for picturing air pol- lution in small temporal and spatial scales. Mobile monitoring of air pollution could be a
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Volume 87 • Number 1
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