Air Quality & Ionizing Radiation

CDC Yellow Book 2024

Environmental Hazards & Risks

Author(s): Audrey Pennington, Armin Ansari

Although air pollution has decreased in many parts of the world, it represents a major and growing health problem for the residents of some cities in certain industrializing countries. Polluted air can be difficult or impossible for travelers to avoid; the risk is generally low, however, for otherwise healthy people who have only limited exposure. Conversely, those with preexisting heart and lung disease, children, and older adults have an increased risk for adverse health effects from even short-term exposure to air pollution.

Air Quality

Travelers, particularly people with underlying cardiorespiratory disease, should investigate the air quality at their destination. The AirNow website provides basic information about local air quality by using the Air Quality Index (AQI) (Table 4-01). The World Air Quality Index project shows real-time air quality and air pollution data for >10,000 air stations in >80 countries around the world, and the World Health Organization posts historical data on outdoor air pollution in urban areas.

Dust masks, surgical masks, and bandanas offer limited protection against severely polluted air. When air is severely polluted (e.g., during wildland fires), the best protection strategies are to avoid prolonged time spent outdoors and to be aware of guidance or directives from local health or emergency management officials (see Wildfire Smoke Factsheet: Protect Your Lungs from Wildfire Smoke or Ash [PDF]). Respirators are specifically designed to remove contaminants from the air or to provide clean respirable air from another source. The National Institute for Occupational Safety and Health (NIOSH) provides a testing, approval, and certification program for respirators. Parents should be aware that NIOSH does not currently certify respirators for children.

Travelers should be mindful of, and limit exposures to, outdoor and indoor air pollution and carbon monoxide (Table 4-02). Secondhand smoke from smoking tobacco is a primary contributor to indoor air pollution. Other potential sources of indoor air pollutants include cooking or combustion sources (e.g., kerosene, coal, wood, animal dung). Major sources of indoor carbon monoxide include methane gas ranges and ovens, unvented gas or kerosene space heaters, and coal- or wood-burning stoves. Ceremonial incense and candles are asthma triggers that often are not recognized.

Table 4-01 Air quality index levels

Good 0 to 50
  • Satisfactory air quality
  • Air pollution poses little or no risk
Moderate 51 to 100
  • Acceptable air quality
  • Some pollutants could represent a moderate health concern for members of sensitive groups
Unhealthy for sensitive groups 101 to 150
  • Members of sensitive groups might experience health effects
  • General public not likely to be affected
Unhealthy 151 to 200
  • Everyone could begin to experience health effects
  • Sensitive groups might experience more serious health effects
Very Unhealthy 201 to 300
  • Health alert: everyone might experience more serious health effects
Hazardous 301 to 500
  • Health warnings of emergency conditions
  • Entire population is more likely to be affected

Table 4-02 Strategies to mitigate adverse health effects of air pollution

Indoor air High levels of smoke (e.g., from cooking and combustion sources, tobacco, incense, and candles) Long- term travelers and expatriates Consider purchasing indoor air filtration system
    All travelers Avoidance
Outdoor Air Poor air quality (high levels of air pollution) or areas potentially affected by wildland fires Travelers with preexisting asthma, chronic obstructive pulmonary disease, heart disease Limit strenuous or prolonged outdoor activity
    All travelers Facemasks (offer limited protection)


Travelers might visit flooded areas as part of emergency, medical, or humanitarian relief missions. Water damage to buildings can lead to mold contamination. Mold is a more serious health hazard for immunocompromised people and for those who have respiratory problems (e.g., asthma). To prevent exposures that could result in adverse health effects, travelers should avoid areas where mold contamination is obvious, and use personal protective equipment (PPE) such as gloves, goggles, waterproof boots, and NIOSH-approved N95 or higher respirators when working in moldy environments. To learn more about mold and respirators, see the Centers for Disease Control and Prevention (CDC) website, Respiratory Protection for Residents Reentering and/or Cleaning Homes that Were Flooded. Travelers should anticipate the environment to which they are traveling and bring enough PPE, because supplies might be scarce or unavailable in the countries visited. Travelers should keep hands, skin, and eyes clean and free from mold-contaminated dust. For additional information, review CDC recommendations, Mold Cleanup and Remediation.


Background radiation levels can vary substantially from region to region, but these variations are natural and do not represent a health concern. Several regions in the world have high natural background radiation, including Guarapari (Brazil), Kerala (India), Ramsar (Iran), and Yangjiang (China), but traveling to these areas does not pose a threat to health. By contrast, travelers should be aware of and avoid regions known to be contaminated with radioactive materials (e.g., areas surrounding the Chernobyl nuclear power plant in Ukraine and the Fukushima Daiichi nuclear power plant in Japan). These areas have radiation levels that greatly exceed background levels and represent a substantial health and safety risk.

The Chernobyl nuclear power plant is located 100 km (62 miles) northwest of Kyiv. The 1986 incident that occurred at that facility contaminated regions in 3 republics—Ukraine, Belarus, and Russia—but the highest radioactive ground contamination is ≤30 km (19 miles) of Chernobyl.

The Fukushima Daiichi plant is located 240 km (150 miles) north of Tokyo. After the accident in 2011, the area within a 20-km (12-mile) radius of the plant was evacuated. Japanese authorities also advised evacuation from locations farther away to the northwest of the plant. Because Japanese authorities continue to clean the affected areas and monitor the situation, access requirements and travel advisories change. The US Department of State recommends against all unnecessary travel to areas designated by the Japanese government to be restricted because of radioactive contamination. For up-to-date safety information or current travel advisories for any country, see the US Department of State’s website or check with the US embassy or consulate in that country.

In most countries, areas of known radioactive contamination are fenced or marked with signs. Any traveler seeking long-term (more than a few months) residence near a known or suspected contaminated area should consult with staff of the nearest US embassy, and inquire about any advisories regarding drinking water quality or purchase of meat, fruit, and vegetables from local farmers.

Radiation emergencies are rare. In case of such an emergency, travelers should follow instructions provided by local authorities. If such information is not forthcoming, US travelers should seek advice from the nearest US embassy or consulate.

Natural disasters (e.g., floods) might displace industrial or clinical radioactive sources. In all circumstances, travelers should exercise caution when they encounter unknown objects or equipment, especially if the objects have the basic radiation trefoil symbol or other radiation signs (see examples). Travelers who encounter a questionable object should avoid touching or moving it, and notify local authorities as quickly as possible.

The following authors contributed to the previous version of this chapter: Armin Ansari, Suzanne Beavers

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