DST ObservAir Manual de instrucciones - Página 18

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5.4. Operational settings for common applications

Table 9 provides typical BC concentrations and operational settings for

some common sampling scenarios. Note that the guidance provided is

approximate and mostly meant to serve as an illustrative guide: Some

applications may not be well described/served by the parameters listed.

Average BC

(µg/m

)

Ambient:

Low

Background/rural

(0 to 1)

Ambient:

Medium

Typical

(0.3 to 5)

Ambient:

High

Dense Urban

(5 to 50)

Emissions capture

Extreme

(direct source)

(> 100)

Medium/High

Mobile/Personal

(0.3 to 50)

Table 9. General settings for several monitoring applications

Ambient monitoring: When deploying the ObservAir as a static network

•

node over long periods (weeks or months), the flow rate should be set

as low as possible to maximize filter life and reduce the maintenance

effort, especially when network sites are remote or numerous. Ambient

monitoring applications typically require data with low temporal

resolution – hourly measurements are often sufficient – and this helps

reduce the flow rate requirements. Referring to Table 8, it can be seen

that the minimum flow rate setting of 25 ccm provides suitable hourly

measurements for nearly all BC concentrations. However, it should be

noted that this achieves a nominal BC measurement resolution that is

~10% of the average concentration, which may not be sufficient for all

applications (e.g., regulatory monitoring). If greater resolution is desired,

flow rate should be increased to the values listed in Table 9. Similarly,

special consideration should be given when conducting long-term

monitoring in rural or remote areas with BC concentrations < 0.5

. In these scenarios when filter loading is low, it is generally

µg/m

advisable to operate the sensor at a high flow rate setting (100 to 200

ccm) to maintain BC measurement integrity.

ObservAir Operating Manual

Flow rate

Time

Filter life

(ccm)

Resolution

High

Low

High

(100 to 200)

(1 hour)

(Weeks/Days)

Medium

Low

High

(50 to 100)

(1 hour)

(Weeks/Days)

Low

Medium

(25 to 50)

(1 hour)

(Days)

Medium

Very low

(50 to 100)

(10 to 60 sec)

(Hours)

High

Low

(100 to 200)

(2 to 10 sec)

(1 day)

Emissions source characterization: The ObservAir can be configured to

•

characterize emissions from stationary exhaust stacks, vehicle tailpipes

and other pollution sources. When sampling emissions directly, do not

exceed the ObservAir's maximum temperature, relative humidity range,

and pollution concentration ratings (Table 3). As with other instruments,

the ObservAir may require that emissions from the source be diluted,

cooled, and/or dried. For transient monitoring applications, such as

engine testing, measurements are typically required every 2 to 10

seconds, and therefore the ObservAir's sample flow rate must usually

be set >100 ccm to maintain adequate measurement resolution. When

sampling over long periods (stack monitoring over hours or days), the

sample flow rate may be lowered to 25 or 50 ccm to maximize filter

life, especially when concentrations are highly elevated. Sampled

concentrations depend on the source and flow conditioning system

implemented (e.g. diluter), but it is not unusual for BC concentrations

to exceed 100 µg/m

when capturing emissions directly.

Mobile monitoring: When sampling from a mobile platform,

•

measurements must be logged as fast as possible to maintain adequate

spatial resolution required for the air pollution maps that are ultimately

generated. Therefore, the ObservAir should be configured to log

concentration data every 2 to 10 seconds at the maximum flow rate

setting of 200 ccm to maximize the temporal resolution of both BC and

gas concentration measurements. Always operate the ObservAir inside

the mobile platform (e.g. car or van) with an electrically conductive

sample line running outdoors. Do not mount sensors on the exterior of

mobile platforms without the dedicated DST mount and enclosure.

When mounting the ObservAir inside the mobile monitoring platform,

take care to minimize exposure to mechanical vibrations, excessive heat

and/or direct sunlight over extended periods.

Personal monitoring: Personal monitoring guidelines largely mirror

•

those provided for the mobile platform: Operate the sensor at a high

sample flow rate (100 to 200 ccm) to maximize the quality of BC

measurements collected every 2 to 10 seconds. Depending on the

application and concentrations sampled, some consideration may be

given optimizing the flow rate for filter life (e.g., each filter lasts a full 8-

hour workday). The sensor may be mounted inside a bag or from a

strap (such as those provided by DST), but take care to clip an

electrically conductive sample line to the subject's lapel or other

appropriate location.

ObservAir

Operating Manual