Monday, September 14, 2009

Frequently Asked Questions: (1) Primary vs Secondary Particulate Pollution?

PM pollution is a mix of primary and secondary sources.

By definition, primary pollution, is a direct emission source and forms a significant portion of the PM pollution, in the form of soot from the coal and diesel burning, also known as black carbon. A good portion of these emissions is also called organic carbon. Besides the carbon, the primary PM emissions also include metals in various forms. For example, the metals in coal, after combustion get vented through a chimney, along with a multitude of other pollutants.

Other primary pollutants include sulfur dioxide, nitrogen oxides, volatile hydrocarbons, methane, carbon monoxide, and carbon dioxide.

The secondary pollution is due to chemical transformation of the primary emissions. In case of PM, the secondary components include sulfates from sulfur dioxide emissions, nitrates from nitrogen oxide emissions, and organic aerosols from hydrocarbon emissions. The path and the quantity of chemical transformationation depend not only on the strength of the pollutant emissions, but also on their mix. In an atmospheric chemical mechanism, the number of interlinkages can run as long as 300 equations (among the known studies).

Most of the secondary pollutants, sulfates, nitrates, and secondary organic aerosols, form part of the fine PM (PM2.5).

Other secondary pollutants include ozone.

A primary source, which is not a direct product of combustion activities, but dependent on the combustion activities, is re-suspension of the dust. Along the corridors, depending on the silt loading, the road dust is known problem. This emission, though a primary source, depends on the local conditions –vehicular activity, relative humidity in the air to support the re-suspension and the silt loading on the roads.

In a measured sample of PM, the secondary pollution is known to form a significant portion of the fine PM, which is a vital indicator for health impacts. Hence, any decision to control PM pollution needs to be a multi-pollutant strategy, in order to maximize the cost effectiveness of the measures.

See other FAQ's.


NucEngineer said...

The following quotes are from the 2007 IPCC report. How much confidence does this verbage portray given the [error bar] levels and the stated “low” levels of understanding?

“The direct RF of the individual aerosol species is less certain than the total direct aerosol RF. The estimates are:
sulphate, –0.4 [±0.2] W m–2;
fossil fuel organic carbon, –0.05 [±0.05] W m–2;
fossil fuel black carbon, +0.2 [±0.15] W m–2;
biomass burning, +0.03 [±0.12] W m–2;
nitrate, –0.1 [±0.1] W m–2; and
mineral dust, –0.1 [±0.2] W m–2.

“Black carbon aerosol deposited on snow has reduced the surface albedo, producing an associated RF of +0.1 [±0.1] W m–2, with a low level of scientific understanding. Other surface property changes can affect climate through processes that cannot be quantified by RF; these have a very low level of scientific understanding.“

You can read this yourself:
IPCC AR4 Report,
Working Group 1: The Physical Science Basis of Climate Change,
Chapter 2, Changes in Atmospheric Constituents and Radiative Forcing,
Page 132

How can anyone be more certain of the sum of factors than in the certainty of the individual factors? Error analysis 101 is the total error is the square root of the sum of the square of the errors. For the list of individual aerosol species above, the total and error would be -0.42 [±0.36].
Oh, for heavens sake, that means cooling! The scientific understanding is LOW. Oh yeah, the model told me so! And a 1% change in low level cloud cover globally, that would be a radiative forcing 10 times greater than the above, and the understanding of clouds and how to include them in the models is very low. Keep drinking the Cool-aid.

Sarath Guttikunda said...

Dear NucEngineer,

Thank you for your comments. However, please note that the blog piece has little to do with radiative forcing and more for local air pollution and related health impacts. You will find relevant information on local efforts to control air pollution in a growing number of cities at

With regards,