The answer, frankly, is that nobody really knows.
"We don't have any official information to release to the public yet," says Dr Tek Chheng Eap, Chief of Respiratory Medicine at the National Paediatric Hospital.
"Every time we seek information, they say [the situation is] not alarming yet."
"They" is the Office of Air Quality, Noise and Vibration Management, which sits under the Department of Pollution Control of the Ministry of Environment.
An official at the Office of Air Quality, who prefers to remain anonymous, assures us that "air quality in Phnom Penh is good".
To back up his claim, he shows us the monthly measurements of carbon monoxide, sulphur dioxide and nitrogen dioxide, which are all safely below international limits.
These measurements have been taken regularly since 2005, using passive samplers, which look like laboratory test tubes placed at roadsides.
However, there are only three in Phnom Penh and, as they do not technically collect ambient data, "the results obtained do not allow comparison to the WHO guidelines", according to a 2006 report on Urban Air Quality Management.
However, the same report notes that "despite the stations being on roadside, the concentrations still do not exceed international guidelines for ambient air quality".
Does that mean we can breathe a sigh of relief?
Not quite, because crucial data on TSP (total suspended particulates) and PM10 (particulate matter with a diametre equal to, or less than 10 micrometres) are not routinely monitored.
In addition, according to the 2006 report, "ambient concentrations of particulate matter appear to be very high, with likely severe impacts on the health of residents of Phnom Penh".
Tek Chheng Eap worries about the increase of traffic and its effect on respiratory illnesses.
"You can develop chronic bronchitis, asthma might be exacerbated, and respiratory infection, the main cause of mortality for children under 5, is a real danger," he says.
However, the Office of Air Quality official gives several reasons to support his belief that the city's air quality is under control.
Cambodia's industry is comparatively light, and he also believes there are fewer secondhand vehicles imported than before.
Furthermore, he claims that the quality of fuel has improved recently, and that many car owners have converted to liquefied petroleum gasoline, or LPG, because of the high price of petrol.
Finally, there is less use of wood and charcoal as energy sources for cooking stoves, and many roads have been paved, resulting in lower levels of dust re-suspension.
Yet, in his presentation, Chanrithy Chuon cited increased secondhand vehicle imports as one of the key transport issues, as well as poor information on fuel quality and the smuggling and adulteration of fuels.
He also listed the enforcement of vehicle inspection and maintenance regulations as an action point.
In terms of the use of wood and charcoal, a 2006 study by GERES (Groupe Energies Renouvelables, Environnement et Solidarites) found that people in the capital consume nearly 100,000 tonnes of charcoal annually.
While this may be less than before, it is still extremely high.
On a more positive note, road dust seems to be less problematic.
"We need to recognise the changes that have been made and also the effort to clean the roadsides; these are good signs," says Tek Chheng Eap.
The municipality is also planning to establish a Better Air Quality project. It aims to establish an institute to manage air quality in the city.
In the meantime, is there anything we as citizens can do?
Tek Chheng Eap says we can personally contribute to improving Phnom Penh's air quality.
"I think everybody has a role to play in helping reduce pollution, like avoiding using the car and trying not to travel during rush hour.
"I hope in the future there will be mass transport and fewer cars.
"There should be more efforts to improve green spaces in the city, and as for the power supply - if that's better, there will be less generators, which is a huge step."