This study assessed the effects of repeated exposure to environmentally realistic levels of two urban air pollutants nitric acid vapor (HNO3) and ozone (O3) - on tracer particle clearance from the rat respiratory tract. The measurement of particle clearance efficiency is important because failure of this function could contribute to a buildup of foreign matter in the respiratory tract. Separate groups of rats (30 rats per group) were exposed nose-only for 4 h/day, 3 days/wk (a surrogate for an air pollution episode) for 40 wk to 4 atmospheres: purified air; 0.15 ppm O3; 50 μg/m3 HNO3; and 0.15 ppm O3 + 50 μg/m3 HNO3. At 4 wk prior to the end of the exposure, the rats inhaled radiolabeled tracer particles nose-only for 30 min. A clearance measurement protocol was then followed to estimate the rates of early and late clearance. Early (presumably upper respiratory tract) clearance was monitored during the 48 h following tracer deposition by the analysis of radioactivity excreted in the feces, while late (presumably deep lung) clearance was characterized by a combination of chest counting and 30 day postexposure sacrifice radioactivity analyses. The exposure to O3, both alone and in combination with HNO3, produced a more than 30% (statistically significant) delay during the initial phase of upper respiratory tract clearance, and all of the pollutant exposures may have stimulated deep lung clearance. The directions of these effects were the same as those observed previously when rats were acutely exposed to O3- containing atmospheres.

Rats were exposed for up to 3.75 h to 0.20-0.80 ppm O3 under conditions of rest and treadmill exercise up to 30 m/min, 20% grade, to assess the importance of exposure duration, O3 concentration, and exercise on lung tissue injury. Focal lung parenchymal lesions increased in abundance and severity in response to the three variables; however, exercise was the most important. Lesion response to exercise was greater than that predicted by a simple proportion to estimated effective dose of O3. The results emphasize the importance of including exercise in assessment of possible adverse health effects of exposure to airborne pollutants.

Respiratory tract injury resulting from inhalation of mixtures of ozone (O3) and nitrogen dioxide (NO2) and of O3 and formaldehyde (HCHO) was studied in Sprague-Dawley rats under exposure conditions of rest and exercise. Focal inflammatory injury induced in lung parenchyma by O3 exposure was measured morphometrically and HCHO injury to the nasal respiratory epithelium was measured by cell turnover using tritium-labeled thymidine. Mixtures of O3 (0.35 or 0.6 ppm) with NO2 (respectively 0.6 or 2.5 ppm) doubled the level of lung injury produced by O3 alone in resting exposures to the higher concentrations and in exercising exposures to the lower concentrations. Formaldehyde (10 ppm) mixed with O3 (0.6 ppm) resulted in reduced lung injury compared to O3 alone in resting exposures, but exercise exposure to the mixture did not show an antagonistic interaction. Nasal epithelial injury from HCHO exposure was enhanced when O3 was present in a mixture. Mixtures of O3 and NO2 at high and low concentrations formed respectively 0.73 and 0.02 ppm nitric acid (HNO3) vapor. Chemical interactions among the oxidants, HNO3, and other reaction products (N2O5 and nitrate radical) and lung tissue may be the basis for the O3-NO2 synergism. Increased dose and dose rate associated with exercise exposure may explain the presence of synergistic interaction at lower concentrations than observed in resting exposure. No oxidation products were detected in O3-HCHO mixtures, and the antagonistic interaction observed in lung tissue during resting exposure may result from irritant breathing pattern interactions.

The US and Mexico share a common history in many areas, including language and culture. They face ecological changes due to the increased frequency and severity of droughts and rising energy demands; trends that entail economic costs for both nations and major implications for human wellbeing. We describe an ongoing effort by the Environment Working Group (EWG), created by The University of California's UC-Mexico initiative in 2015, to promote binational research, teaching, and outreach collaborations on the implications of climate change for Mexico and California. We synthesize current knowledge about the most pressing issues related to climate change in the US-Mexico border region and provide examples of cross-border discoveries and research initiatives, highlighting the need to move forward in six broad rubrics. This and similar binational cooperation efforts can lead to improved living standards, generate a collaborative mindset among participating universities, and create an international network to address urgent sustainability challenges affecting both countries.