Shot of the Geraldton Esplanade from the air
by @jthomas84_

According to the recent data released by the World Health Organisation, Geraldton has the highest levels of air pollution of any city in Australia. An article from The Guardian (link) (the UK based publication, not the local newspaper) made the assertion based on the spreadsheet of data put out by the World Health Organisation (WHO) (link).

But before you start wearing a gas mask full time, we want to go through the data to find out what it all means exactly, and if the assertion that Geraldton really has the highest level of pollution really stacks up.

How exactly is air pollution measured?

Before we lose you with too many scientific terms, it may pay to explain exactly how air pollution is measured.

Monitors measure two types of air pollution particles. Larger particles are called PM10. Smaller (invisible) particles are called PM2.5.

Sandeep Chowry, an environmental engineer, explains more on Quora (link)

Coarse dust particles (PM10) are 2.5 to 10 micrometers in diameter. (i.e. µm which is basically a millionth of a meter.) Sources include crushing or grinding operations and dust stirred up by vehicles on roads. These tiny particles which are about 30 times smaller than the width of a hair on your head are small enough to get inhaled past our defensive nose hairs and into our lungs.
Fine particles (PM2.5) are 2.5 micrometers in diameter or smaller, and can only be seen with an electron microscope. Fine particles are produced from all types of combustion, including motor vehicles, power plants, residential wood burning, forest fires, agricultural burning, and some industrial processes. While PM10's story ends at the lungs, PM2.5 can pass from our lungs into our blood supply and be carried throughout our bodies thereby making them "the invisible killer"

The 12 month median PM10 particle rate for Geraldton was 22µg/m3 (micrograms per cubic metre), which is worse than Sydney, Perth or even New York. The WHO guidelines for a 12 month median for PM10 is 20µg/m3.

The PM2.5 particle rate for Geraldton was 10µg/m3. The WHO guidelines for a 12 month median for PM2.5 is 10µg/m3.

To put that in comparison, Perth, with 2 million people, measured 17µg/m3 for PM10 particles, and 8µg/m3 for PM2.5 particles, slightly better than Geraldton.

But here's where it gets interesting.

Geraldton doesn't have a monitoring station for PM2.5 particles. We only measure PM10. So the World Health Organisation used a formula to essentially guess what the PM2.5 particles are for Geraldton.

Here's what the Mayor of Geraldton had to say

We asked Mayor Shane Van Styn, who had seen the WHO data, what he thought about the assertion that Geraldton was the most polluted city in Australia.

"Geraldton is a windy city on the coast," said Mr Van Styn. "The majority of PM10 pollution in Geraldton would be background, natural dust and sea salt, not man made toxic fumes like in a city. And the WHO data doesn't include places like Port Hedland or Karratha. The level of 22 µg/m3 is what you would expect for a windy, coastal city in Australia with higher than usual background crustal dust levels.

"Finer fraction PM2.5 is typically more from products of combustion, but importantly, PM2.5 for Geraldton was converted from PM10 measurement, not measured. So this number is likely going to over-estimate the actual PM2.5 levels for Geraldton.

"I would challenge that you cannot call any city which only just exceeds the WHO guidelines and mostly based on background levels, a “polluted city”, which conjures up images of smoke laden air, which is chokingly hard to breathe in.

"When looking at other pollutants such as NO2, SO2 and ozone, Gero would not even rate a mention, compared to large cities such as Sydney, Melbourne and Perth."

So what's causing the high PM10 pollution levels exactly?

According to historical data from the Dept of Environment Regulation (link), the days on which Geraldton's PM10 levels spiked dramatically were largely due to dust. Given Geraldton is directly downwind from Southgates sand dunes, surrounded by broadacre farming, and has a busy port in the middle of town, dust is an obvious culprit. Moreover, Geraldton is right on the coast and is so windy the trees grow sideways, so a decent percentage of the particles in the air are sea salt.

Is that all?

A report on heavy metals in the air in Geraldton from 2011 (link) stated that "Air monitoring data during ship loading have indicated that dust levels up to 430 µg/m3 TSP and 150 µg/m3 PM10 have been detected within the Port. If ship loading is allowed to occur during on-shore winds then there is potential for dust to reach nearby residences."

Why doesn't Geraldton monitor PM2.5 ?

Great question. Geraldton suffers for several months each year when nearby farmers burn off stubble, blanketing the town in smoke, and Iluka's refinery is directly south (upwind) of the town. But the Department of Environment Regulation doesn't monitor pollution levels for PM2.5 in Geraldton yet.

We asked Mayor Van Styn if he supported the idea of setting up facilities to measure PM2.5 in Geraldton, to put people's minds at rest, and to find out exactly what our PM2.5 is.

"Absolutely. There’s no reason why we shouldn’t. We’re already doing the work to measure PM10, surely we can do the same for PM2.5.

"The issue of pollution has been raised fair and square by the World Health Organisation. Let's make a call to the Department of Environment Regulation to measure the air quality for PM2.5 in Geraldton and find out exactly what the levels are."

NACC (Northen Agricultural Catchment Council) CEO Richard McLellan said air pollution is something to be taken seriously. "Of all the forms of pollution, air quality is the one that most that affects human health," he said. "With water you generally know if you're drinking polluted water. But when it comes to air quality, most people don't know if they're breathing polluted air."

Mr McLellan also spoke to the indirect implications of air pollution. "There's social implications, but there's also economic. It affects tourism and people wanting to visit a place. This issue needs to be nipped in the bud as soon as possible."

Everything Geraldton has contacted the Department of Environment Regulation for comment, and at time of publication has not had a response. We will publish their response to the matter when we receive it.