Download Airzone newsletter April 2010

Otago’s air quality newsletter
April 2010
CONTENTS
p3 Fluctuating weather
patterns influence
monitoring results
p4 Do’s and don’ts for
heat pump
management
p4 Business praised for
collaborative attitude
to discharges
What makes our
atmosphere tick?
The National Environmental
Standard (NES) regulating air
pollution levels in Otago will be
well known to many people
reading this.
However, the atmosphere’s components
may not be as readily apparent to
some. The permanent gases in the air
include nitrogen (78 percent), oxygen
(21 percent) and argon (less than 1
percent). They are all in fairly constant
proportions in the lowest section of the
atmosphere.
Otago Regional Council (ORC) air
quality scientist Deborah Mills says that
while the atmosphere is almost wholly
made up of oxygen and nitrogen, it’s
the rest of what lies within it that makes
it interesting.
Deborah says water vapour is a key
element in the atmosphere and the
most variable. It can be expressed
as relative humidity as well as in
many other measures. In the upper
atmosphere ozone absorbs UV
radiation, and CFCs work to break
down that ozone.
While these constituent components
together form the atmosphere, gravity
keeps it all near the surface.
Troposphere is weather
nerve centre
Ninety percent of all molecules are
within 16km of the earth’s surface and
exert a pressure equal to 14 pounds per
square inch, which can’t be felt. There
are relationships in the atmosphere
between pressure, density, temperature,
and altitude.
The troposphere is the area where all of
our weather occurs, including cyclones,
and anticyclones. What’s known as the
tropopause is the break between, and
the stratosphere goes from there to
about 50km up. An area of maximum
ozone absorbs ultra-violet rays and
heats up the air, so the temperature
profile reverses.
With rising altitude, density goes
down, and therefore pressure and the
temperature go down as well. Overall
the structure of the atmosphere has
several layers and is measured by what
is called a temperature profile.
The troposphere climbs up to 12km
into the atmosphere, or roughly the size
of Mount Everest. The zone is defined
by the temperature decreasing by
about 6.5degC for every kilometre. “If
you started at 20degC at the surface,
by the time you reached the top of
the troposphere, it would be roughly
minus 50 degrees,”Deborah said. This
is without any outside influences like
weather fronts or wind.
The NES set by the Ministry for the
Environment (MfE) in 2004 set air
quality standards which set the limits
for various pollutants including sulphur
dioxide and nitrogen dioxide. This was
designed to cover acid deposition,
adverse health effects, and smog.
Of particular importance to Otago
people is that standards were set for
particulates, specifically PM10 - small
particles with an aerodynamic diameter
of less than 10 microns. The size of a
particle determines its potential impact
on human health.
AirZone - April 2010
“PM10 is what gets past your nose”. Particles less than about six
micrograms (mcg) in diameter can usually penetrate the bronchial
passages, while those less than two mcg in diameter can penetrate
and be deposited in the lungs.
The sources of pollutants include industry, whether coal, diesel,
or wood-fired, and agriculture in the form of burn-offs. However,
domestic heating is by far and away the primary source of Otago’s
pollution problems, whether it’s coal or wood-based.
Generally there are three major influences on air quality: the rate of
emissions (which relates to some degree to what is being emitted);
meteorology, which plays a huge part in whether pollutants are
transported and-or dispersed into the atmosphere or if they hang
around; and topography, which to some degree is tied to the
meteorology.
Within meteorology, wind speeds, temperatures and atmospheric
instability are the three most important factors in determining how
emissions are dealt with in the atmosphere. Wind can distribute
pollutants from point sources like chimneys to create an overall
air quality condition, or act to disperse pollutants, diluting their
concentration in the atmosphere.
Don’t judge atmospheric
stability by its cover
Deborah says stability in the atmosphere
isn’t what it seems. “We tend to think
of being stable as a good thing, but in
air quality the reverse is true. “A stable
atmosphere traps pollutants at the
surface, but it’s an unstable atmosphere
that moves pollutants up and out.”
The unstable atmosphere is really the
theoretical,normal atmosphere, Deborah
says “We live in the troposphere,and,
according to the laws of physics, as you
go up in altitude, gases become less
dense, and temperatures decrease.”
This sets up an unstable condition as
warm air rises.
On a warm, sunny day the surface
warms up, which in turn warms the air
above it. This warmer air wants to rise,
taking with it whatever is in it. However,
there are occasions when temperature
increases with height. For instance, on
a cold, clear night, the Earth’s surface
cools rapidly and strongly, which in turn
cools the air right above that surface.
“You end up with cooler, denser air
nearer the surface, which is unable to
rise. This is a stable condition,” Deborah
says. “It’s trapped by warmer air above
it, and the pollutants are trapped near
the surface.”
This is known as a temperature
inversion and typically happens in
Pollution in the troposphere above Arrowtown
2 - AirZone - April 2010
Figure 1. Structure of the Atmosphere
winter: overnight under a clear sky with
cold temperatures. The inversion usually
‘breaks up’ in the morning once the
surface starts to warm.
Topography, or how a place sits on
the landscape, is the third key element
governing air quality. Places like
Alexandra Clyde, Arrowtown, and
others sit at the bottom of surrounding
hills.
Cold air drainage is common in those
places at night, where air that has
cooled from higher altitudes moves
downward. This may enhance the
temperature inversion, and may
bring with it pollutants from higher
elevations.
Smog in Alexandra
Fluctuating weather patterns
influence monitoring results
As many people in the Air Zones will
know, the ORC has to regularly monitor
particulate matter levels (or PM10) in
towns where the Government’s National
Environmental Standard (NES) is likely to
be exceeded.
Summary monitoring results for 2009
indicate that there are pockets of the
Airzones in the region where more work
on reducing pollution is needed. This
includes Lawrence, where intermittent
monitoring showed a large percentage
(21 percent) of high-pollution days, and
Milton, which recorded the highest oneday average of 145 micrograms.
In Alexandra there were 40 exceedances
in 2009, compared with 75 in 2008 and
35 in 2007. ORC air quality scientist
Deborah Mills says the 2008 figures
need to be interpreted carefully because
of the very strong La Nina event which
influenced them, skewing them relative
to other years.
Deborah says the 2008 results were
different from other years because of
the large-scale weather patterns that
were present at the time. “Certain
weather conditions aggravate the air
quality situation in winter, causing
smoke to be trapped at the surface.
These conditions include very cold
overnight temperatures, clear skies, and
not much wind.”
Temperature inversions form near
the surface and smoke can’t rise and
dissipate in the atmosphere. “Everything
stays near the ground so all of the
smoke coming from chimneys hangs
around and elevates the PM10 readings.”
How do inversions make
their presence felt?
These inversions come about through
large high pressure ridges which
often hang over the South Island,
characterised by clear sunny days, and
minimal wind.
During a La Nina event, these high
pressure ridges occur more frequently
– and perhaps with longer duration
– than during the El Nino events,”
Deborah said.
“In 2008, we were in quite a strong La
Nina mode during the beginning of the
year and it extended into winter.
Continuous air monitoring started
in 2005 after the Ministry for the
Environment (MfE) introduced a new
national environmental standard for air
quality.
Deborah says that while the
introduction of the new standard
has been a steep learning curve for
many people, they have been quick to
appreciate the reality of the problem,
adapt accordingly and become attuned
to what constitutes unhealthy air.
Deborah says people are vitally
interested in the results of the
monitoring, and are keen to get
updates on their collective compliance.
150
125
100
Otago people can take a bow for their
growing awareness of the importance
of reducing air pollution in the region.
75
Average
Highest
50
Second Highest
Third Highest
25
0
Otago PM10 levels (2009)
So, as temperatures cooled down in
May and emissions from fires picked up
we ended up with numerous ‘highpollution’ days in May, something we
don’t normally see.”
El Nino is predicted to last until late
autumn and then shift to neutral
conditions. On that basis Deborah
thinks this year will look like last year,
not 2008.
From the end of May the ORC will be
putting out a weekly report recapping
trends so far this year and summarising
current trends. It will be available
on the ORC website (www.orc.
govt.nz) and via email. To go on the
electronic distribution list simply email:
[email protected]
3 - AirZone - April 2010
Do’s and don’ts for heat
pump management
Anyone who has purchased a heat
pump will have done so with maximum
energy efficiency gain and power
savings in mind. However, the Energy
Efficiency and Conservation Authority
(EECA) says those gains will only
materialise if people use their pumps
smartly - otherwise those power bills
may not show any savings at all.
EECA suggests people learn to use the
timer on their pump, and set it so it
comes on an hour or so before they get
home or get up in the morning.
Some installers suggest leaving the heat
pump on 24 hours day, seven days a
week, but you should only do this if
there are people in the house all day
and you want to keep the house warm
at night Otherwise, you’re wasting
energy, EECA says.
It uses less energy to warm the house
up when you want it than to keep it
constantly warm when there’s no-one
there.
Remember you can use the timer to
start warming up the house before
you get home. EECA recommends only
heating spaces that you are actually
using and turn the heat pump off when
it’s not needed
Shut doors, windows, and curtains to
keep the heat in, and don’t set the
temperature higher than you need
it. An ideal and comfortable working
temperature is regarded as 18 to
22degC, and if required, 16degC
overnight. Thorough maintenance
of the interior and exterior units is
recommended, including ensuring the
filters are cleaned annually.
A heat pump’s efficiency is gauged by
its “Co-efficient of Performance” or
COP. Depending on its size, a good heat
pump has a COP of about 3.5, which
means it produces 3.5kW (or units) of
heat for every kilowatt of electricity it
uses.
You can calculate the COP by dividing
the heating output by the power
input. For more information go to
the Energywise website at www.
energywise.govt.nz
Business praised for
collaborative attitude
to discharges
Otago industries generally have a
responsible attitude toward mitigation
of air pollution and its effects. This is
fortunate and timely since discharges to
air have to improve.
PM10 (or very small particles in the
air) is the major cause of air pollution
in winter, although it comes from
industrial emissions in far smaller
amounts than household fires and
burners. The National Environmental
Standards (NES) for air quality were set
by the Government in 2004.
When the daily average reading for
PM10 is more than 50 micrograms it is
classified as a high pollution day; and
more than one such occurrence will be
in breach of the NES after 2013.
Otago Regional Council (ORC) director
resource management Selva Selvarajah
says his staff have been advising existing
industrial consent holders who are
4 - AirZone - April 2010
looking at renewal that they should be
looking at emission rates of between 25
and 50 per cubic metre to secure longterm consents.
They are being urged to consider
options to achieve better discharges
such as installing a baghouse: air
pollution control equipment used in the
dust capturing, separation or filtering
process, or upgrading boilers.
Dr Selvarajah says the council has been
encouraging businesses during the
past two to three years to extend their
consent periods from an average of 10
to 15 years to 35 years-the maximum
available under the Act.
If the technology is not affordable
immediately ORC will allow two to three
years to make the transition to 2013 by
granting 35-year consents.
“Generally industries who use boilers
have been working co-operatively with
us to achieve ORC requirements,” Dr
Selvarajah said.
“There have also been good responses
from industries outside the polluted
airsheds. ORC is happy that these
industries did not use dilution as
a solution and secured long-term
consents with upgrades.” However, the
ORC recognises that such upgrades are
not cheap.
Otago Regional Council
70 Stafford St
Private Bag 1954
Dunedin
03 474 0827
0800 474 082
www.orc.govt.nz