Historic sulfur dioxide emissions are the most likely explanation for increased porosity in rock surfaces near industrial areas of Murujuga, Western Australia, according to the third annual report of the government-funded Murujuga Rock Art Monitoring Program (MRAMP).
Murujuga is a cultural landscape across the Burrup Peninsula and Dampier Archipelago containing an estimated 1 million to 2 million petroglyphs. The engravings record the relationship between Ngarda-Ngarli Traditional Owners and the landscape over at least 50,000 years. The Murujuga Cultural Landscape was added to the UNESCO World Heritage List in July 2025.
The monitoring team compared rock surfaces across the peninsula and found a statistically significant pattern: rocks closer to industrial sites were more porous than those farther away. Increased porosity indicates measurable structural differences and may leave surfaces more vulnerable to fading or flaking if deterioration continues.
Earlier monitoring had identified nitrogen dioxide as a possible contributor, but the available data could not clearly distinguish its effects from those of other pollutants, including sulfur dioxide. The expanded evidence now points more strongly to sulfur dioxide released historically by industry and shipping.
In the atmosphere or on rock surfaces, sulfur dioxide can form sulfuric acid. The researchers say that acid can dissolve manganese and iron oxide minerals in the dark surface coating, producing porosity. Their evidence indicates that emissions peaks in the past, rather than current pollution levels, were responsible for the long-term pattern.
The conclusion draws on three years of monitoring, including 186,000 measurements of rock-surface condition, air-quality observations, continuous rainfall-chemistry sampling and more than 5,500 laboratory tests on rock samples. The researchers say these lines of evidence are most consistent with historic sulfur dioxide emissions, possibly acting together with microbial activity on the rock surface.
During the monitoring period, the team did not observe acid rain, and air quality generally remained below environmental thresholds developed through the program. It also found no measurable acceleration of deterioration linked to current pollution. The report cautions, however, that this does not prove that present-day pollution has no effect at all; current methods can exclude only impacts large enough to detect.
The program’s final report, planned for next year, will investigate interactions among air quality, rock surfaces and microbial communities. Researchers will also develop long-term environmental criteria addressing sulfur dioxide, nitrogen dioxide, ammonia and ozone, while ongoing monitoring continues.
