Aerosol particles have been shown to trigger cardiovascular and respiratory diseases in populations living in polluted regions, depending on their size and composition. Although fine aerosol particles have been found to reach the lungs and the blood stream, their acute effects are related to the fraction of ultrafine aerosol particles (i.e., UFPs, d < 0.1 μm). In the present study, the concentration of UFPs (d = 0.02–0.1 μm) was monitored in Merida (Yucatan) between April 2017 and July 2018. Additionally, the total aerosol particle concentration (d > 0.03 μm), PM₁₀, PM_2.5, criteria gases, and meteorological variables, were also monitored. The average UFPs concentration over the full sampling period was found to be 2,070 ± 1,831 cm^-3, with events of peak concentrations as high as 55,117 cm⁻³. The average daily UFP profile is bimodal, with peak concentrations observed around 07:00 and 20:00 h LT. The correlation of the UFP with other measured variables suggests that the UFPs peaks observed in the morning and at night are likely caused by primary vehicular combustion particles. In contrast, atypical high concentrations of UFPs were occasionally observed around noon LT, which are likely of secondary origin and the result of new particle formation promoted by photochemistry. Overall, UFPs are the major contributor to the total particle number concentration, and they are likely an important contributor to PM_2.5 in Merida during the morning hours, with clear anthropogenic sources.

气溶胶颗粒已显示出可在生活在污染地区的人群中引发心血管和呼吸系统疾病，具体取决于其大小和组成。尽管已发现细小气溶胶颗粒到达肺和血流，但其急性影响与超细气溶胶颗粒（即UFPs，d <0.1μm）的比例有关。在本研究中，于2017年4月至2018年7月在梅里达（尤加坦州）监测了UFP的浓度（d = 0.02–0.1μm）。此外，总气溶胶颗粒浓度（d> 0.03μm），PM ₁₀和PM _2.5，标准气体和气象变量也进行了监测。在整个采样期间内，UFP的平均浓度为2,070±1,831 cm ^-3，具有峰值浓度高达55,117 cm ^-3的事件。UFP的每日平均轮廓是双峰的，在LT的07:00和20:00 h观察到峰值浓度。UFP与其他测量变量的相关性表明，在早晨和晚上观察到的UFP峰值可能是由主要车辆燃烧颗粒引起的。相反，在中午LT周围偶尔会观察到非典型的高浓度UFP，这很可能是次生的，而且光化学促进了新颗粒形成的结果。总体而言，UFP是总颗粒数浓度的主要贡献者，它们很可能是早晨时段梅里达PM _2.5的重要贡献者，有明确的人为来源。