A study by researchers at The Johns Hopkins University
found an association between increasing levels of indoor
particulate matter pollution and the severity of asthma
symptoms among children. The study, which followed a group
of asthmatic children in Baltimore, is among the first to
examine the effects of indoor particulate matter pollution.
The results are published in the February edition of the
journal Environmental Health Perspectives.
Particulate matter is an airborne mixture of solid
particles and liquid droplets. The solid particles come in
numerous shapes and sizes and may be composed of different
chemical components. Fine particles measure 2.5 microns or
less in size (approximately 1/30th the diameter of a human
hair) and can penetrate deep into the body's respiratory
system. Coarse particles fall between 2.5 and 10 microns in
diameter. These larger particles can also enter the
respiratory system and can be produced indoors through
activities such as cooking and dusting. The Environmental
Protection Agency regulates outdoor levels of fine particle
pollution but does not have a standard for coarse particle
pollution. There are no regulations for indoor
For the study, researchers from the Center for Childhood
Asthma in the Urban Environment — a joint center of
the Johns Hopkins schools of Public Health and Medicine
— followed 150 asthmatic children, ages 2 to 6, for
six months. Environmental monitoring equipment was used to
measure the air in the child's bedroom over three three-day
intervals; measurements were taken at the beginning of the
study, after three months and again after six months.
Ninety-one percent of the children who participated in the
study were African-American and from lower socioeconomic
backgrounds, and spent most of their time indoors.
"We found that substantial increases in asthma symptoms
were associated both with higher indoor concentrations of
fine particles and with higher indoor concentrations of
coarse particles," said Meredith C. McCormack, lead author
of the study and an instructor with the Johns Hopkins
School of Medicine.
For every 10 micrograms per cubic meter of air (ug/m3)
increase in indoor coarse particle concentration, there was
a 6 percent increase in the number of days of cough, wheeze
or chest tightness, after adjusting for a number of
factors. For every 10 ug/m3 increase in fine particles
measured indoors, there was a 7 percent increase in days of
wheezing severe enough to limit speech, and after adjusting
for various factors, a 4 percent increase in days on which
rescue medication was needed. In many cases, the level of
indoor fine particle pollution measured was twice as high
as the accepted standard for outdoor pollution established
by the EPA.
"Children spend nearly 80 percent of their time indoors,
which makes understanding the effects of indoor air very
important," said co-author Gregory B. Diette, an associate
professor in the School of Medicine and co-director of the
Center for Childhood Asthma in the Urban Environment.
Co-author Patrick Breysse, a professor in the School of
Public Health and co-director of the Center for Childhood
Asthma in the Urban Environment, said, "Improving indoor
air quality and lowering indoor PM concentrations may
provide additional means of improving asthma health,
especially for children living in inner cities." Additional
authors of the study are Elizabeth C. Matsui, Nadia N.
Hansel, D'Ann Williams, Jean Curtin-Brosnan and Peyton
The research was supported by National Institute of
Environmental Health Sciences, U.S. Environmental
Protection Agency and the Johns Hopkins NIEHS Center for Urban Environmental