The picture is a microphotograph of ambient (street-)dust, collected in Jakarta on August 9th, 2020, after major rainfall which ended a spell of ten dry days. The sample material has been washed down and concentrated by the rain and was collected with a tape lift from a specially prepared surface.
So, what’s good about it? What is the good news? – Many things: What we see is mainly mineral dust (by visual estimation) consisting predominantly of quartz grains and a very few other mineral (such as plagioclase and muscovite). The yellowish coloring of the grains comes from iron oxide.
We note the conspicuous absence of asbestos fibers, although the sample was collected close to a traditional residential area with Eternit roofs.
Asbestos constitutes a significant health risk. We also note the very small proportion (<5%) of soot which usually comes from the unfiltered exhaust of diesel engines. Soot, amorphous carbon, forms opaque particles which can be identified by their peculiar shape. Finally, the grains in the sample are much larger than 5 μm (five micron). This is good news, because particles smaller than 5 μm could enter the alveoli of the lungs and remain there, causing damage and respiratory problems. Other very minor, subordinate components in the sample are microplastic (I have seen less than five particles), pollen, seeds and other plant particles.
Of course, it might be the case that the sample was not perfect and has missed the fine fraction of the atmospheric dust and of course, more samples and more studies are necessary (as always) to get closer to the final truth. However, the current observation is encouraging.
So, where does the dust come from? – A good question, indeed! It has been established that areas in Europe and north America receive mineral dust from as far away as the Sahara desert and from other desert areas in the Middle East. But where does the Jakarta dust come from? We can only speculate. Possible sources are desert areas in China and the Australian outback. The few plagioclase grains in the samples (plagioclase is only metastable) are probably from the fall-out of volcanic ashes (?Merapi, ?Mt. Sinabung, etc.). Volcanic origin of the quartz grains can be excluded because quartz is not a common mineral in volcanic matter, therefore it must have come from somewhere else …