A new study from POSTECH (Pohang University of Science and Technology), led by Professor Hyung Joo Lee and integrated PhD student Na Rae Kim, evaluated how well ground monitoring networks represent nitrogen dioxide (NO₂) exposure and how the exposure varies by socioeconomic status across South Korea. The research team estimated ground-level NO₂ concentrations using satellite remote sensing data at a 500-meter spatial resolution, which was an essential factor in their analysis. The findings were recently published in the international journal Environmental Science & Technology.

NO₂ is a criteria air pollutant primarily emitted from combustion sources, such as on-road and off-road vehicles and power plants. It is regulated under South Korea’s Clean Air Conservation Act due to its association with adverse health effects, particularly on respiratory health. Because NO₂ has a relatively short atmospheric lifetime and reacts readily with other atmospheric components, spatially resolved data are critical for accurate exposure assessment. However, ground monitoring networks are not evenly distributed, making it difficult to represent population-level exposures adequately. To address this challenge, the POSTECH team employed satellite remote sensing NO₂ data from the Tropospheric Monitoring Instrument (TROPOMI), producing a detailed spatial map of NO₂ exposure at a 500-meter resolution nationwide.

Using these high-resolution data, the researchers assessed whether the national ground monitoring network accurately captured population exposure to NO₂ across metropolitan cities and provinces. Since ground monitoring data are used as benchmarks for evaluating compliance with air quality standards, it is crucial to ensure they reflect real-world exposure levels. The study revealed that ground monitors underestimated NO₂ exposure by up to 11% in Gangwon-do (northeastern part of South Korea) and overestimated exposure by as much as 61% in Jeju-do (the largest island in South Korea). Moreover, the representativeness of ground monitoring was not strongly associated with the number of monitors in a region, suggesting that merely adding more monitors may not improve accuracy in reflecting population exposure.

The study also examined the differences in NO₂ exposure by socioeconomic status within each region. The results showed that areas with higher socioeconomic levels, based on individual housing prices and insurance premiums per capita, demonstrated higher NO₂ concentrations. This finding was supported by consistently positive correlations, ranging from 0.53 to 0.92 for housing prices and from 0.41 to 0.91 for insurance premiums. Interestingly, this contrasts with previous findings in other countries, where socially disadvantaged groups often experience higher NO₂ exposure. The researchers attributed this difference to South Korea’s unique economic development history. During the rapid industrialization in the 1970s and 1980s, major roads and residential areas were constructed nearby. Proximity to these roads was highly valued for commuting convenience, driving up housing demand and prices. Furthermore, in the 1970s, the government established industrial complexes in many parts of South Korea, drawing job seekers and eventually becoming hubs for high-paying employment. As a result, wealthier populations have concentrated in areas that show higher NO₂ air pollution today.

Professor Hyung Joo Lee emphasized, “Strategic placement of ground monitors, accounting for both pollution hotspots and population distribution, is essential for precise exposure assessment.” He added, “While our study focused on NO₂, other air pollutants also need to be evaluated to develop a more comprehensive understanding. Given that the health impacts of air pollution are influenced by factors such as medical infrastructure, neighborhood environment, and underlying health conditions, a more integrated and multidisciplinary approach is crucial to fully understand and address the public health implications of air pollution.”