April is one of the months that the sand blows in from the Gobi desert. I have relatives who are visiting Beijing in April, and I advised them to take face masks, as well as over the counter throat lozenges. Be prepared for bad pollution, and consider yourself lucky if you don't experience it. Good luck.

I have been in Beijing twice in April-May and the air quality had been bad. I have never suffered from allergies, but the winds, pollution, pollen and whatever else is in the air made my eyes suffer. I had itchy eyes and often watery eyes.

Had to constantly use Visine to get some relief.

So, make sure you take your allergy medicines as well as something for the eyes.

Pollution is always bad and the newspapers always say it is not really bad although the American Embassy keeps reporting the daily log showing that it is truly very, very bad.

Presently the pollution is really at its worst and the winds are actually blowing the stuff towards southern Japan.

The air is so bad some days that one cannot see any of the skyscrapers at all. Visibility is so poor.

So, enjoy Beijing, but take care of allergies. Have a great trip.

While it is possible to generalise about the likely state of Beijing's air in April on average, there's nothing that can be said about how it might be on particular days, which may include days when the air quality is as poor as anything recently seen.

The single most important influence on air quality in Beijing is the weather, and in particularly the wind. It is true that there's typically more wind in April, which is a help. It does occasionally bring in sand from high ground to the northwest, but not very often, and that's a different issue altogether.

If you want to have some idea of what's going on, you need to look at:

http://www.twitter.com/Beijingair

which carries hourly information from a machine on the roof of the Beijing embassy. Click further through the link provided if to understand the measurements. For a sober discussion of the situation, see:

http://www.chinafile.com/airpocalypse-now-china-tipping-point

Most importantly, ignore anything anyone says about health issues here. The only meaningful advice is that from the doctor dealing with adult and child in question. Take him or her information about pm2.5s, sulfur dioxide, nitrogen oxides, ozone, lead, mercury, and other elements of China's atmosphere (Guangzhou included), and get his advice.

Personally, and although I've spent several years in Beijing, am very fond of the city, and am about to return, I certainly wouldn't take my children there at the moment. But I'm NOT a medical professional. Consult yours. He may recommend N95 masks, or have something else to say.

I'm sure everyone would find it interesting to hear what that is.

Pollution is greatly weather related and, just like weather, cannot be predicted that far in advance. Yes it is sand storm season but I have lived there four years now and only witnessed one. Maybe I happened to be traveling when others have occurred.

OP here -- had a sobering visit with my allergist/asthma doctor of 20 years today. We are in the San Francisco Bay Area so he has had a number of patients who told him their issues in China. I also have spoken quite a bit with co-workers and families who have moved here in the last year from China (Beijing and Shenzhen), our family members in Shanghai, as well as emailed with friends currently living in China.

What we've learned confirms what people wrote above. Some people become very sick, and others are fine. People advised to stay within access of a medical facility.

Our doctor was saying, "How NECESSARY is this trip?" and "Of course I can't stop you from going, but....". He indicated that he would have us double existing medications for allergies 2 weeks before the trip, and start inhalers for me and the 5-year old. For the trip we would take stronger inhalers, prednisone, buy a nebulizer, NH95 masks, epipens and antibiotics. He said, "I would need you to be your own emergency room." He advised us not to go to Beijing or Shanghai, which have both had very bad readings in the past year. This is of course an issue, since we have flights into Beijing and out of Shanghai.

BMarieL

I think you may have days with bad sand storm impact but you may also have days that are just fine. I am including here a link to photo album page on my blog that includes photos of the Forbidden City which were taken in April .....vs. the photos of TianAnMen square were taken in mid-March ---- which shows how different the air / weather can be:

http://site.chinafinds.com/travel/photo-albums/china-%E4%B8%AD%E5%9B%BD/china-beijing/

So this is a bit of luck type of a situation.

Here is a doctor's point of view: http://www.myhealthbeijing.com/2012/04/breathing-clean-in-beijing-lets-separate-fact-from-fiction/
I live there 9 months per year and had no consequence. If you only pass by as a tourist it will have no long term effect on you. Maybe some short term discomfort, which I never had. But I can understand that some people are more sensitive.