Contribution of Tourist and Transit Vehicle Emissions to Air Pollution on Slovenian Roads during Summer

Air pollution, particular aerosols and their precursors, has a substantial impacts on local weather and climate by increasing cloud condensation nuclei and altering how much solar energy is absorbed or reflected by the atmosphere. To accurately model these impacts, emissions inventories, dispersion models, and receptor models perform best when using high-resolution inputs. Currently, Europe has adopted regulations aimed at improving air quality and encouraging detailed studies of emission sources. While emission records over time indicate an overall decline, the transport sector has grown in recent decades, mostly because an annual increase in vehicle numbers. Although advancements in vehicle technology aim to reduce emissions, concerns remain that the increasing number of vehicles on the road may hinder this progress. Additionally, a critical knowledge gap has been identified in the bottom-up approach used to estimate emissions from transit vehicles and tourism activities.

Our study identifies and evaluates the issue of vehicle congestion on the roads during the summer, primarily driven by transit demands and tourism activities.

The methodology to capture an understanding of traffic-related emissions from the summer vehicle peak was developed. Summer traffic peak was estimated by comparing the summer vehicle numbers with those of other parts of the year. Vehicle numbers were recognized by vehicle counters located on a Slovenian highway junction in the year 2021. Moreover, the study also revealed the emissions from the summer traffic peak, calculated by the COPERT emission model.

We observed that, on an average summer day, there are up to 11,520 additional vehicles on Slovenian roads. Our study found that in the year 2021, on average, there were increases of 85%, 19%, 34%, and 17%, with up to 88%, 33%, 63%, and 32% increases in motorcycles, buses, passenger cars, and light duty vehicles. Meanwhile, it is recognized that the decrease in heavy duty vehicles is, on average, −14%. Those results help to understand contributions to estimation of urban source of emissions, which lead to improve the inputs data for the dispersion and additional atmosphere models. The methodology could also be copied in other places.