From the ground, most glass and steel office skyscrapers and other tall buildings look clean and sparkly. When you work in the buildings, however, you get up close and personal with those windows, and they are anything but clean a lot of the time. That’s why they need constant cleaning, which is why no business with good sense passes up the chance to get a free quote for commercial building window cleaning.

But what is it that is making the windows so dirty? There are several sources of dirt on most city office windows:

1. Wind

Australia’s major cities are virtually all coastal, and about 80 percent of people live and work in coastal zones. These are naturally windier areas, and any wind coming onto land whips up dirt and dust from the ground, which then finds its way to those windows where it clings on.

When the wind is bringing a lot of dust and dirt, you’ll find that some buildings are naturally affected more than others. That of course is because some buildings shelter each other from the wind. The more direct wind your office building gets, the more likely the wind is the chief source of your dirty window woes.

2. Air Pollution

Melbourne, Sydney, Perth and Brisbane may not have the levels of pollution that they experience in Beijing or New Delhi, but any urban conurbation packed with cars and people generates air pollution. Any pollution that gets airborne such as smoke, pollen, soot, mold and others easily get stuck on office windows. If you have a lot of heavy traffic running right under your office windows, or a lot of flowering trees, for instance, then you have a greater chance of being affected by this kind of particle pollution.

In parts of the country with a cooler winter, the colder and denser air traps that pollution even more effectively, which leaves it suspended in the air for longer, giving it more opportunity to get stuck on your office windows. Warmer summer air tends to blow it away more quickly.

3. Particles in Water

If groundwater is used to clean your office windows, it can look clean after the initial hose or pressure washer blast, but as the water dries, you might notice dirt particles lingering on there. It’s frustrating, of course, but it’s the natural result of using regular groundwater. The reason? While groundwater is clean and potable, it contains various kinds of sediment and other minerals which get stuck on the glass as the water molecules dry off.

It’s a common misconception that rainwater makes windows dirty. While in some cities where rainwater is heavily polluted by local industrial activity, the rain in most Australian cities doesn’t contain any dirt particles that would cause so much dirt accumulation on windows. Why do windows look dirtier after the rain, then? The reason is that those aforementioned particles are stuck on the window, which get further smeared across the surface by the rain, making it look dirtier.

4. Cleaning Solution Residue

When office window cleaning is left to anyone but the real professionals, it is very common for cleaning solutions used to leave behind residues that make the windows appear as dirty or worse than before they were cleaned. It might not immediately be visible, so your cleaners are long gone by the time you see it. Professional cleaners are much better at gathering up all of this residue, and also won’t leave streaks behind.

5. Protective Screens

If your windows are often opened to save on the air conditioning costs, you may well have screens in place to keep out mosquitoes, wasps and other flying pests. These screens, however, collect all the same dust, dirt and other pollutants that make your windows look dirty. In fact, they do it even more effectively, which means even if your windows are clean, the soiled screen makes them still look dirty from both sides.