by Ian Williams Goddard
Since Environmental News Service published claims that military aircraft are spraying "contrails" that make people sick,  there has been an explosion of such claims. While there are known cases of military experimental spraying over American cities,  it was unclear to me whether these recent claims of a causal connection between contrails and illness are accurate or post hoc fallacies. 
The central premise of the claim that contrails are sprayed chemicals is that "normal contrails" dissipate within seconds. Therefore, contrails that persist or expand and blend with others into a haze are not mere water-vapor condensation but are instead composed of some kind of nonevaporating substance.
I had the fortune to witnesses such contrail phenomena myself and took many photographs. It is my conclusion that what I observed seen in the following photos was the result of atmospheric conditions, and furthermore, I believe these phenomena may account for the majority of "spray-trail" reports I've heard.
Here are two composite images of four photographs I took:
Each side-by-side photo was taken within seconds of the other at one of two locations in Rockville Maryland, on February 11, 1999. It was an unusually warm day for February, reaching around 65 degrees Fahrenheit. While the surface air was dry, there was a haze starting several thousand feet above. All the contrails slowly spread out into this haze, exactly like accounts of "spray-trails" around the country. But I believe the contrails did not form the haze, rather, the humidity of a natural haze preserved the contrails.
[Here's a satellite image taken on the same day. Notice how the contrail proliferation over centeral-to-Eastern Maryland follows the north-to-south formation of the cloud mass and thus humidity as per the thesis I advance here.]
This contrail proliferation appeared to have been caused by a bubble, or pocket, of dry and unusually warm air hugging the land above which there was very cold air. In an area between these two thermal regions -- an area containing a few thousand vertical feet of atmosphere -- condensation would naturally form. The high humidity in that area would naturally preserve contrails simply because nothing is evaporating in that area.
The next photograph taken on another day demonstrates that contrails hang and expand in a humid area and evaporate outside that area:
The photo shows three contrails persisting only within the clouds. The contrails had long-since evaporated in the area outside the clouds where they once existed. I observed this occur and predicted that it would as I watched the first jet approaching the clouds. This confirms to my satisfaction that natural humidity sustains contrails and that it is an error to assume that "normal" contrails do not hang and expand.
It might also appear that a fluffy substance is falling off an expanding contrail. Here's another photo I took on Feb. 11, notice that it could appear that the lower and most expanded contrail is dropping something fluffy (cobwebs?).
The structure of that fluffy "fall off" was consistent with a subtle natural fluffy texture appearing within the haze overhead. This photo shows a natural thin cloud structure intersecting with a large expanded contrail.
Notice the similarity of expanded-contrail structure and the natrual cloud structure. That fluffy structure manifested itself naturally in the haze layer. The contrails simply provided "grist for the mill," and as such, were inducted into the unique cloud-formation mechanics of that day. There was no epidemic of illness that I could detect after February 11, and these contrails were right over where I live.
 Environmental News Service: (a) Contrails Mystify, Sicken Americans. William Thomas, January 8, 1999. (b) Mystery Contrails May Be Modifying Weather. William Thomas, January 12, 1999.
(c) 1999 Ian Williams Goddard