Boundary Layer Profiling using various techniques for air quality assessments Dave DuBois Ilias Kavouras and George Nikolich Division of Atmospheric Sciences Desert Research Institute Las Vegas, NV

Overview of Larger Study Study purpose is to measure and interpret air toxics in an urban airshed - Albuquerque, New Mexico Three air toxics monitoring sites, at existing city stations Each site measures semi volatile organic compounds, volatile organic compounds, carbonyl compounds and heavy metals Samples collected in a 1 in 6 day frequency for one year

Overview of Meteorological Study One objective of the larger study is to determine the impact of meteorological conditions (diurnal, daily, and seasonal time scale) on air toxics concentrations and human exposure To meet this, we designed a field program with two intensive monitoring periods (IMP) – one in winter (Feb 2008) and one in summer (June 2008)

IMP Study Design Albuquerque is located in a river valley (Rio Grande River runs north-south) in the high desert (elev m MSL) Mountain range immediately to the east of city (peak at 3255 m MSL) Conceptual model of up/down valley drainage and some up/down slope wind patterns Measurements focused on capturing diurnal patterns of slope flows and temperature inversions

Typical View of Winter Stagnation Downtown NorthPlaza office tower is 107 m (highest building in NM)

Network Design Obtain vertical profiles of T/RH/winds using tethered balloon system (Vaisala) Obtain pseudo-profiles of T/RH with HOBO transect from river to mountain (U23) Use Sandia Aerial Tramway to obtain T/RH profiles to top of mountain range Use laser ceilometer (Vaisala CL31) to locate heights of aloft aerosols and compare with T/RH profiles

Profiling Network Up/Down Valley Winds HOBO

Vertical Profiles on Mountain

Tram Box Tethered Balloon System HOBO U23 Tethered Balloon CL31 ceilometer

Network Design This is a cross section, looking north, up the river

Winter Balloon Profiling Very shallow surface layer, less than 100 m deep Feb 17

Summer Balloon Profiling Again we commonly see deeper layer in am 6/24

Compare with ceilometer Plot of backscatter from ground to 7700 m AGL clouds June 24, 2008 Computed mixed layer height using gradient method – It did well when there are no clouds

Tethered Balloon System Positives Detailed profiles of T/RH/winds (up to 0.5 Hz sampling rate) Can carry other instruments such as particle counters, VOC, O3, NOx samplers Can be operated as a met tower with instruments at several levels Negatives Limited in height by FAA, requires NOTAM Requires at least one person, better two people to operate Limited used in winds over 10 m/s (also storage issues when windy) Requires several cylinders of helium and AC power

Pseudo-Profiles with HOBO Positives Inexpensive Fairly high temporal resolution (1 sec) Easy to install and download data Small, so it was easy to hide them Good accuracy considering cost (+ 0.3°C, 3% RH) Battery powered Set and leave Negatives Sensor time response slow for moving objects (e.g. on a car or tram) Our installations were influenced by micro scale ground heating, so siting is important

Tram profiles Positives Able to get profiles in an location difficult otherwise in complex terrain Can carry more instrument payload than tethered balloon system (e.g. heavy batteries) Good PR for tramway owner Fun to ride Negatives Limited to when the tram operates Requires fast response sensors due to speed of tram (~6 m/s) Ground heating effects when approaching towers Heating effects of tram car is noticable Download the data daily and recharge batteries Coordination with tram operators

Laser Ceilometer Positives Continuous sampling of backscatter, cloud heights Gives a profile every 10 s Unattended sampling Eyesafe laser All weather operation Heights from ground to 7.7 km in 10 m increments Can provide mixed layer heights after processing Negatives Requires data processing (Matlab or similar) and interpretation skills Our set up required a lap top, serial interface, AC power Point measurement in the vertical Useful to have web cam operating at same time to verify clouds

Uses of Data Urban scale wind field characterization using diagnostic model – CALMET Driver for trajectory and plume modeling Exposure modeling Method development for mixed layer height using ceilometer