FAQ’s on Asian Dust and Pollution

By Dr. Dan Jaffe

Last updated: August 2003

Because of the large number of requests for information, I have decided to write up this list of Frequently Asked Questions on Asian dust and pollution transport. Hopefully this can serve as a primer on the topic for those unable to access or interpret the scientific literature. Obviously reading the published peer-reviewed articles is a better source. Most of what I have written below is based on the findings in our peer-reviewed articles, but I’ve also speculated a bit.

See also the following links:

Back to Dan Jaffe’s homepage

Link to Jaffe group real-time data, peer-reviewed publications and forecasts

What is the focus of your research?

My group studies long-range transport and sources in the Pacific of ozone, aerosols (both pollution and dust) and toxics, such as mercury and persistent organics.

Does only dust get transported from Asia or do pollutants also come across the Pacific?

Both dust and pollution can be transported. My group first detected pollution (see our GRL paper published in 1999). A year later dust from a major Asian dust storm was transported across the Pacific and detected by a number of researchers in North America. Since then, we have now identified many cases of this transport.

Does this mean that we don’t need to worry about our own local air pollution?

NO! Absolutely not. Dust and pollution which is coming from 8000 km away will nearly always contribute less to your local air pollution then local sources. As Pogo said “We have met the enemy, and he is us!”. It would be a total misinterpretation of these results to blame local air pollution problems on long-range transport.

So then does this mean long- range transport of dust and pollutants is not important?

Well, I didn’t say that. These pollutants add to local sources. To explain this I can use the EPA’s Air Quality Index (AQI). An AQI of 0 represents no pollution (impossible) and for most pollutants an AQI of 100 is the allowable limit where there are demonstrable health effects. So lets say your background air (the air that blows into your region) is normally at an AQI of 20 and your local air pollution adds 70, for a total of 90. You are below the allowable limit and below the level with significant health impacts, but not by much. Now say the background increases to 30 (say from sources far away), now you are at an AQI of 100, not good.

Does Asian dust and pollution transport only occur when there is a major dust storm in Asia?

No! This is just when the newspapers like to cover it! The pollution sources in Asia are “on” all the time. There is probably a small amount of pollution that gets transported across the Pacific all the time. The large dust storms only occur when high surface winds are present and when the soil is relatively dry. This usually happens after a frontal passage and is most common in spring. The large dust particles get picked up and the resulting concentrations in Asia can be enormous. Fortunately, such high levels do not persist for long. The larger dust particles fall-out over time, are removed by rain and disperse, so that the concentrations are decreasing with time. Nonetheless, occasionally we do see very high aerosol levels from Asian dust storms.

Do the dust or pollution levels ever reach hazardous conditions?

For the people living in Asia, these dust and pollution levels are associated with health impacts. Once these get transported to North America, the levels are much lower. The highest we have seen at ground level is from the 2001 dust event. In this event, PM10 and PM2.5 reached approximately 2/3 of the US air quality standard at several sites along the west coast (see Jaffe, Snow and Cooper 2003 paper in publication list). This is a level associated with health effects for some people. The 2001 dust event was similar to, but larger, then the event we saw in 1998 (see Husar et al paper in publication list).

Is the material transported at the surface?

Occasionally it can be transported this way, but we believe that most of the transport occurs in the range of 3-6 km elevation. This is why aircraft observations add greatly to data obtained from surface sites.

Does this only occur in spring?

We don’t have much data in other seasons. Spring was when we thought the transport would be strongest, so for this reason, so far we have focused our efforts on spring observations. Our observations in 2002 and 2003 suggest that transport of Asian pollutants and forest fire smoke can occur during late spring and summer.

How do I know if Asian dust or pollution is present?

Probably you won’t notice anything. Unless this is a once in 5 year event (10 year, 20 year???). In the April 1998 and April 2001 episodes the large amount of dust produced a strong haziness that was noticed in places that were usually clear. During these events the sun appeared a bit washed out and rather then a bright blue sky, the sky was noticeably whiter. Not like a cloud, but not the beautiful “desert blue” sky either. If you live in an urban area where the sky is usually polluted anyways, you might not notice any impact. Also clouds make it impossible to see the haze from the ground. Except for these dust episodes, you probably won’t see any evidence of other pollutants in the sky.

Doesn’t North American pollution get transported too?

Yes, pollution from NA is transported into the Atlantic and occasionally has been detected over Europe. There are a lot of differences between the NA sources the Asian sources. The Asian sources include not only industrial pollution, but also large amounts of coal by-products, desert dust and emissions from biomass burning (Siberia and Southeast Asia).

Is this problem getting worse or better?

Unfortunately we have few long-term data records to be sure, but there is now evidence that for ozone, the problem is getting worse (see paper by Jaffe, Price, Parrish, Goldstein and Harris in publication list). There is some conflicting evidence on whether Asian sulfur emissions are increasing or decreasing and it probably depends on which chemical species we are talking about. For example dust, nitrogen oxides, persistent organics and mercury all come from different types of sources. It is possible, even likely, that some of these are increasing while others are decreasing.

What tools do you use to study this problem?

My research group measures dust and pollutants. We do this both at a ground station on the Olympic coast of Washington state. This site is called “Cheeka Peak” and it has been operated by the University of Washington for approximately 15 years. My group has operated the site since 1997. In addition we use a small aircraft to obtain vertical profiles of dust and pollutants up to about 6 or 8 km (depending on the plane). Our measurements include carbon monoxide, ozone, aerosols (dust), nitrogen oxides, radon, hydrocarbons and mercury. Through collaboration with Dr. Staci Simonich at Oregon State University, we are also measuring Persistent Organic Pollutants at Cheeka Peak. In addition, we frequently use several global models of atmospheric chemistry and transport including the GEOS-Chem model, being run by Dr. Lyatt Jaeglé and the NAAPS model from the Naval Research Laboratory.

What other tools do you use?

There are a number of products that we make use of to interpret our data and to time our aircraft sampling (the ground observations take place continuously). These tools are satellite imagery and computer simulations, which predict where the pollutants will be transported. None of these is by themselves perfect, but putting these all together gives us the most complete picture. Satellite imagery can be particularly deceptive in that most satellites do not “see through” clouds. Also it is very difficult to get quantitative information from the satellites. The forecast models are very valuable to time our flights. However these cannot be more accurate then the weather forecasting models which are at their core. Links to all of these can be found on the forecasts page listed above.

Can you tell me what is happening right now?

You are welcome to investigate the satellite images, model forecasts and real time data that my group is putting on our website.

Who is funding this research?

Our work is currently supported by NSF, EPA and NOAA.

How important is Asian dust and pollution transport to air quality in North America?

Well, this is the 6 million dollar question. To be truthful, the answer is “we don’t know”, but we are starting to get a better idea.

Ok, time for me to stick my head out the window and see what’s happening!