A question: many of the precursors to O3 formation are VOCs, and (my study area) trees contribute a significant fraction of VOCs to the atm. Tree canopies also can change the boundary layer mixing in cities, making it harder for wind to sweep out the goop in the air.
Were you able, in your work for this paper, to contact anyone and explore whether elevated CO2 levels decrease tree metabolic rates and thus decrease VOC emissions?
Unfortunately there isn’t yet much understanding of the large amount of interannual variability in blocking [high pressure systems] seen in the last few decades. So it is very hard to make a prediction of what might happen to blocking in a climate change experiment.
Whilst it is important to consider the possible effects of climate change on problems such as this I think it is best to emphasise that the dominant cause is the availability of the precursor pollution, and that reducing this pollution [by making changes to transport systems and industry] is the best way of tackling this problem.
Biogenic VOCs are highly reactive and the emissions are substantial especially in humid, warm seasons. I wonder in the case of blocking patterns leading to drought and well above normal temperatures if biogenic VOC emissions might actually decrease? Short of the vegetation actually dying from the drought of course.
I know this study focuses on ambient air pollution, but has anyone looked into trends to see if we (humankind in developed nations) stay indoors more during heat waves, thereby subjecting ourselves to increased levels of indoor air pollution ? Common sense tells me to stay in where its cool when its hot. Should we be asking if indoor air pollution will become a bigger issue as summers get hotter due to the effects of Global Warming?
I have the impression that the prediction of future climate/pollution links is rather speculative.
In the not so long past, the worst pollution was during cold, calm, high humidity weather, at the time coal was used in open fire places, leading to the infamous “pea soup” smog in London, killing elderly people.
Since that time, SO2 and lead were reduced with over 80%, PM10 with over 60% and NOx with over 40% in all Western countries. As NOx is the main driver for low level ozone formation, it’s further reduction should have a large impact.
About biogenical VOC’s: these are mainly formed in summer, where high temperatures and secondly high light/photosynthesis are the primary drivers. Natural VOC’s exceed anthropogenic emissions with a factor 3-8
#1 and #3: Yes, the emissions of volatile organic carbon (VOCs) from vegetation play a role in ozone formation. In cities like Atlanta with lush vegetation, biogenic VOCs together with anthropogenic nitrogen oxides can have a significant impact on regional pollution.
The emissions of biogenic VOCs increase rapidly as temperatures increase. But plants also respond to changing CO2. While some plants may flourish in an enriched CO2 atmosphere, VOC emissions may decrease. And as Dan points out below, vegetation may also suffer from heat or water stress in a changing climate. It’s a complicated picture.
I did not include any of these biogenic effects in my simple sensitivity study. I kept emissions of pollution precursors constant. All I wanted to see was this:
if I increase the long-lived greenhouse gases like CO2 in the model and let the
climate respond, what happens to the patterns of air circulation? What I found
was that stagnation events lasted longer in the future model atmosphere.
On the other hand, Hogrefe et al.  did include the biogenic VOCs that Dano and Dan are talking about. Of the effects listed above, Hogrefe et al.  considered only the temperature effect on biogenic VOC emissions. They found a 10-50% increase in these emissions with climate change over the eastern U.S. Unfortunately there isn’t yet much understanding of the large amount of interannual variability in blocking [high pressure systems] seen in the last few decades. So it is very hard to make a prediction of what might happen to blocking in a climate change experiment.
#2. I agree with Tim that more work is needed to understand what controls cyclone (and anticyclone) variability in the observation record. A number of model studies, such as our own, have found a decline in cyclone number in a future atmosphere. The model trends can be explained with mechanisms such as the flattening of the temperature gradient from equator to pole. Improving our understanding of present-day variability will give us greater confidence in what these models say.
I also agree that tackling emissions of pollution precursors is important. But so long as emissions of pollution precursors remain in a kind of middle range (i.e., above natural levels), we can expect that daily weather patterns will play a role in whether or not we have a bad air day.
A changing climate will influence the daily weather and could have consequences for air quality.
Along with the potential influences of changes in temperature and moisture on biogenic VOC emissions from individual plant species there are likely to be changes in VOC emissions based on longer-term changes in composition of vegetation [for example, KellomÃ¤ki et al. 2001] because of a wide range in VOC emissions among species [for example, Kesselmeier and Staudt, 1999; Kesselmeier et al. 2002]. If climate change results in the large-scale changes in forest species composition as vegetation adapts to a warmer climate as some models suggest [Iverson and Parsad, 1998], these species shifts could influence the rates of emission of biogenic precursors and thus the frequency and intensity of air pollution episodes. The lengthening of the growing season in northern temperate latitudes also suggests a longer period where conditions could increase air pollution risk. I am curious what replacement of spruce-fir and northern hardwood forests with oak and pine-dominated forests in the far northeastern US would mean for ozone attainment in the future.
Kesselmeier, J.K., and Staudt, M., 1999, Biogenic volatile organic Compounds (VOC): An overview on emission, physiology and ecology: J. Atmos. Chem., v. 33, no. 1, p. 23 – 88.
Kesselmeier, J.K.et al.., 2002, Concentrations and species composition of atmospheric volatile organic compounds (VOCs) as observed during the wet and dry season in RondÃ´nia (Amazonia): J. Geophys. Res., v. 107(D20), p. 8053, http://www.agu.org/pubs/crossref/2002/2000JD000267.shtml
In addition to GW contributing to increased pollution, it is also important for laypersons to keep in mind that most human activities that generate GHGs, also generate other forms of pollution to air, land, & water, & many non-environmental harms/costs, when we consider the entire life cycle of products from resource extraction, shipping, manufacture, shopping, consumption, disposal, plus military/government costs associated with protecting/procuring resources/products.
I wish there were better ways to internize a least a few more of the real costs of products and compensate victims better.
Comment by Lynn Vincentnathan — 2 May 2005 @ 1:17 PM