Biogeosciences News

High Smog Levels Seen in Mecca During the Annual Pilgrimage

Surveys of air quality show that smog and other pollutants in Islam’s holiest city during the Hajj are among the worst in the world, prompting the Saudi government to look for ways to clear the air.


In 2012, the Hajj drew 3.5 million Muslims to Mecca for five days of prayer and spiritual enlightenment. The annual pilgrimage, one of the largest annual gatherings of people in the world, also brings dangerous levels of air pollution to Islam’s holiest city.

At a 15 December press conference at AGU’s Fall Meeting in San Francisco, a team of atmospheric scientists and public health experts presented results from a two-year survey of air quality in and around Mecca during this religious pilgrimage, which in recent years has tripled the size of the city.

The Grand Mosque in Mecca is one of several sites Muslims visit during the Hajj. Photo  by Fadi El Binni, Al Jazeera English, CC BY-SA 2.0
The Grand Mosque in Mecca is one of several sites Muslims visit during the Hajj. Photo by Fadi El Binni, Al Jazeera English, CC BY-SA 2.0

They reported dangerously high levels of several pollutants along the pilgrimage route, especially in tunnels through Mecca’s mountains and hills.

Pollution Levels During the Hajj

Pilgrims, also called Hajjis, spend all five days trekking in one large group by foot, bus, car, truck, and even train to sites across and outside of the city, which explains how this annual event churns out so much smog and soot.

“This is a major, major health problem,” stressed Haider Khwaja, a chemist and public health researcher with the University at Albany, State University of New York, and the Wadsworth Center at the state’s Department of Health.

During the 2012 Hajj, the team detected soot and fine particulates at levels 20 times greater than the maximum exposure recommended by the World Health Organization. “These fine particles can penetrate deep into the lungs and then can cause cardiopulmonary and lung diseases,” Khwaja said.

Other atmospheric pollutants, such as carbon monoxide, were more than 300 times greater during the Hajj, noted atmospheric chemist Isobel Simpson from the University of California, Irvine. Some of the readings even surpassed air pollution levels in Beijing, currently the poster child for poor air quality.

Tunnels Concentrate Pollution

Pollution levels, of course, varied along the traditional trek pilgrims take during the Hajj. However, “the surprise was just how very high some of the concentrations that we measured were…especially in the tunnels of Mecca,” Simpson said. Based on surveys from two tunnels that share car and pedestrian traffic, the 58 tunnels through Mecca’s hills and mountains along traditional Hajj routes likely pose the greatest health risk to pilgrims, she explained.

One of Mecca’s tunnels during the 2012 Hajj. Photo by Jahan Zeb
One of Mecca’s tunnels during the 2012 Hajj. Photo by Jahan Zeb

Within one particular tunnel surveyed along the Hajj route, Simpson and her colleagues detected levels of carbon monoxide, benzene, and sulfur compounds at levels high enough to cause short-term health problems such as headaches and nausea, as well as long-term cardiovascular disease.

“Our concern is not only for the citizens of Mecca and the pilgrims, but also for people in the tunnels like police, hotel workers, volunteers” who help direct traffic and ferry pilgrims along the route, Simpson said.

How to Improve Air Quality?

The team pinpointed some of sources of pollution, including cars and trucks used by some Hajjis. One unexpected source of air pollution, for example, came from gasoline evaporation at fueling stations. Installing rubber rings around gasoline nozzles could reduce pollution from this source, Simpson indicated.

The researchers explained that the Saudi government, which contributed funds for these air-quality surveys, recently announced steps to improve air quality in general and specifically during the Hajj. They include setting a national standard to lower benzene levels in gasoline by a factor of five along with restricting single-car vehicles in Mecca during the Hajj, said Azhar Siddique of King Abdulaziz University. Siddique, Khwaja, and Simpson also recommended separation of foot and vehicle traffic through the tunnels, upgrades to tunnel ventilation systems, and enactment of strict vehicle emissions standards, which are currently nonexistent.

An additional 1-2 million Muslims are expected to take part in the Hajj by 2025 said Siddique, which will only add to the holy site’s pollution problems. In addition to the toll on human health, ozone, sulfate, and toxic metals are high enough to corrode architectural and cultural wonders in Mecca such as the Grand Mosque—sites that Hajjis have traveled so far to see, Khwaja and Siddique told Eos.

Future air-quality surveys, as well as data from new sensors along the pilgrimage route, should show whether these moves are sufficient to curb air pollution and bring a breath of fresh air for Mecca.

—James Urton, Freelance Writer

Citation: Urton, J. (2014), High smog levels seen in Mecca during the annual pilgrimage, Eos Trans. AGU, 95(51), 487—488, doi: 10.1002/2014EO510004.

© 2014. The authors. CC BY-NC 3.0