Remember, a pollen producing tree or shrub next to a home can create ten times more exposure than a tree or shrub one or more houses away. Get those high risk trees away from you home.
One rule of thumb - flowers with large blooms usually produce heavy (large particle) pollen. These trees attract insects that transport pollen and do not depend on wind transportation. These trees are generally lower in their allergy potential. Also, "perfect" flowers on trees are desired. A perfect flower is one that has both male and female parts in a single flower - not just male and female parts on the same tree. Perfectly flowered trees include crab apple, cherry, dogwood, magnolia, and redbud.
Trees that are considered to cause less allergy problems are:
Female ash, female red maple (especially the "Autumn Glory" cultivar), yellow poplar, dogwood, magnolia, double-flowered cherry, fir, spruce and flowering plum.