Kim Y.J. (Ed.) Advanced Environmental Monitoring

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7 Aircraft Measurements of Long-Range 91

Keywords: Airborne gaseous, aircraft measurements, long-range trans- boundary,

aerosol sulfate, air pollutants of SO

, NO

, O

7.1 Introduction

The pacific coast of East Asia is a region in which human activities impose a

heavy burden in the form of atmospheric air pollutants such as sulfur compounds

and aerosols, which exhibit an average flow duration from a day to a week in the

low layer of the troposphere (Kim et al. 2001). The emissions of SO

and NO

have

been decreasing or have at least remained steady since 1980 in Western Europe

and North America; however, they are still growing in the Asian region, especially

in northeast countries that are under the shadow of the westerly belt of China.

Although the rate of SO

emission in China has been generally decreasing, the

total amount of SO

emitted is still large (Hatakeyama et al. 2004; Streets et al.

2001). Industrialization in China is one of the main causes of acidic pollution and

aerosol.

The spatial distribution of ocean areas between Korea and China is one of the

important parameters that must be taken into account for an assessment of the

environmental impact of pollution in this region. As a consequence, aircraft

measurements have been incorporated into pollution studies in order to investigate

the long-range transport and distribution of atmospheric pollutants, as demonstrated

by Prospero (1999), Jaffe et al. (1999), Clarke et al. (2001) and Nunnermacker et al.

(2004). Aircraft measurements of air pollution have also been carried out by Kim

et al. (1997) and Han et al. (2006) over ocean areas around the Korean peninsula.

However, these measurements were not sufficient for a complete analysis of the

long-range transport of air pollution or a thorough estimation of the spatial and

temporal distributions of pollution over these ocean areas.

Aerosol sulfate contributes to cloud formation as major cloud condensation

nuclei, and to atmospheric greenhouse effects through atmospheric radiative forc-

ing. The transport of atmospheric particulates in Northeast Asia is closely related

to Asian dust, namely yellow sand dust, which was thoroughly investigated during

the ACE-Asia campaign in the spring of 2001 (Arimoto et al. 2004).

The study of the long-range transport of air pollutants has been carried out by

several aircraft observation campaigns over the seas between Korea and continental

China by various countries of Northeast Asia since 1995 (Hatakeyama et al. 1998;

Kim et al. 2001).

However, in order to precisely analyze the source–receptor relationship of

pollutants in this region and to clarify the effects of pollutants on the regional atmos-

pheric environment and global climate, it is very important to analyze the dynamics

of atmospheric chemical constituents emitted by natural and anthropogenic sources

in both receptor and source regions. A study of the source–receptor relationship of

air pollution was organized under a Korean initiative in 1996 in the form of an

expert working group for the investigation of the long-range trans-boundary air

92 S.-N. Oh et al.

pollutants in Northeast Asia (LTP) with representatives from Korea, China and Japan,

and a number of collaborative experiments have since been performed.

The objectives of our aircraft measurements are to study the spatial distribution

of pollution in the ocean atmosphere between Korea and China, and to improve our

understanding of acidic deposition in the Korean area in relation to processes

affecting long-range trans-boundary transport of air pollutants from China. The

measurements are used to identify the sources and characterize the dispersion

fluxes of atmospheric pollutants over the ocean domain from China to west Korea.

Experiments were carried out during April and October, 2005.

7.2 Measurements, Instrumentation and Meteorology

7.2.1 Flight Strategy

A twin propeller type Chieftain aircraft (US PIPER Co., see Fig. 7.1) was flown

over the downwind area from China above the Yellow Sea between China and

Korea and inland of Korea for comparisons with ground measurements of air

pollution and meteorological data. The dimensions of the aircraft were 10.55 × 3.96

× 12.40 m, and it had a capacity of 350 HP and a normal cruising speed of 370 km/h.

The sampling nozzle was designed to minimize the loss of sampling compounds

and was attached to the bottom of the aircraft. The mass flow controller (MFC,

Tylon) was supplemented to the sampling system to keep the flow rate constant

following changes in altitude.

Four flight strategies, as shown in Fig. 7.2, were adapted with a change in

altitude (from 300 to 2,300 m) in round trips along the longitudinal and latitudinal

flight tracks from the starting point of Kimpo Airport in Seoul for each measurement

period. Experiments were mainly carried out in the afternoon during successive

days during April 15–21 and October 15–22, 2005.

Fig. 7.1 The aircraft (left) and sampling nozzle (right) installed on the bottom of the aircraft

(aircraft size: 10.55 m (L) × 3.96 m (H) × 12.40 m (W), cruising time: 6.9 h, landing weight: 700 LB

(317.5 kg), cruising distance: 1.97 km, limit altitude: 3,000 m, speed: 150 knots (277.8 km/h) )

7 Aircraft Measurements of Long-Range 93

7.2.2 Instruments

Ambient air for gas analysis was introduced into the cabin of the aircraft through a

3/8-in. Teflon tube connected to an air inlet at the bottom of the aircraft.

was measured continuously with a UV pulse fluorescence TECO model

Thermo-43C (Trace Level). NO

concentration was measured with a chemilumines-

cence NO

analyzer (TECO model 43S), which was modified to measure total oxides

of nitrogen. Ozone was monitored with an absorption ozone analyzer (Model 49C,

TECO) with 4-s switching of the light path for its dual-cell system using a UV

photometric method (Table 7.1).

Aerosol number concentrations in five size bins ranging from 0.3 to 10 µm were

continuously monitored with an optical particle counter (Rion, KC-01C). Aerosol

mass concentrations were monitored with PM10 at six ground stations on the

Korean peninsula for comparison with aircraft measurements.

Gas materials and aerosol states were measured every 10 s and the mean value

of the data was averaged over a 1-min interval. The collected data was statistically

analyzed with respect to hourly and daily values, though aerosol number concentra-

tion was analyzed over 2-min intervals. The geographical position of the aircraft

was determined by a GPS β pilot system.

Fig. 7.2 Aircraft flight tracks for the measurement periods

94 S.-N. Oh et al.

and NO

were also routinely calibrated with the span gases. Detection limits

for SO

and NO

were 0.2 ppb in the case of the 10-s average and 0.05 ppb in the

case of the 2-min average. The ozone monitor with a detection limit of l ppb was

also calibrated before and after each flight. All calibrations were performed through

the complete Teflon inlet line. Analyzed gas and geographical location data were

stored in a portable computer. General descriptions for relevant aircraft instrumen-

tation are shown in Table 7.1 Typical flight routes consisted of vertical profiles up

to 3 km and horizontal trans-sections along the longitude over the Yellow Sea.

Aerosol samplings were also carried out at the Tea-An ground station, which is

located on the western tip of Korea (36°44′N, 126°08′E, 20 m above the mean

sea level).

7.2.3 Atmospheric Vertical Structures and Meteorology

On April 15, the observation area around Tea-An was covered by a high-pressure

system with westerly and southwesterly winds. On April 18, the observation area

was dominated by two high-pressure systems centered around North China and the

South-East Sea of Japan. It was cloudy and wind blew mainly from the west and

southwest with a strong wind speed of 10 m/s at a 300-m flight level. On October

15, the Korean region had a comparable day of strong wind from a low-pressure

system in the northwest region of China.

The depth of the atmospheric boundary mixing layer was identified using the

vertical profiles of potential temperature and the water vapor mixing ratio, which

were measured by radiosonde at the Tae-An ground station at a time corresponding

with the aircraft flight, as shown in Fig. 7.3a, b. The observation station of KMA at

Seosan reported a northwesterly wind with a speed between 2 and 4 m/s at the

ground station. The afternoon soundings suggested that the atmospheric mixing

layer in the region reached a height between 1,000 and 2,000 m.

Table 7.1 Description of relevant instruments equipped on the aircraft

Gases Instruments Range Response time Precision

UV fluorescence/TEI <100 ppb 80 s 0.2 ppb

(10-s average)

Chemiluminescence/TEI <100 ppb 60 s 0.05 ppb

(10-s average)

UV photometric/TEI <100 ppb 20 s 1 ppb

(10-s average)

Particle Aerodynamic particle <1,000 cm

1.4 min

Number counter/TSI-3320

Position & GPS/Garmin, GPS-II Position (°) &

Altitude altitude (m)

Atmospheric Radiosonde/USA-AIR3 30 hpa 1 s

Vertical

Structure

7 Aircraft Measurements of Long-Range 95

Fig. 7.3 a Atmospheric vertical profiles using 5-s sensitivity observations of potential tempera-

ture (P.T.), water mixing ratio (W.R.), wind speed (W.S.) and direction (W.D.) at Padori Tae-An

on April 15–18, 2005

(continued)

96 S.-N. Oh et al.

Fig. 7.3 b (continued) Atmospheric vertical profiles using a 5-s sensitivity observations of poten-

tial temperature (P.T.), water mixing ratio (W.R.), wind speed (W.S.) and direction (W.D.) at

Padori Tae-An on October 16–19, 2005

7 Aircraft Measurements of Long-Range 97

7.3 Results and Discussion

7.3.1 Gaseous Species

Statistical analyses of aircraft measurements are shown in Table 7.2, which include

the mean and standard deviation of gas concentrations during the measurement

periods. Mean gas concentrations (ppbv) of SO

, NO

and O

were respectively

2.58, 4.24 and 54 in April and 6.63, 3.74 and 48.8 in October, 2005.

Since the observation area was affected by a high-pressure system on flight days,

we expected that the highly polluted air mass emitted in this area would be confined

to lower altitudes. The concentrations of the three gases at various altitudes were

only measured on April 18 and October 17. The results showed that the highest con-

centrations were measured at an altitude of around 500 m on April 18 and 800 m on

October 17, as shown in Figs. 7.4 and 7.5. The maximum concentration at these

altitudes was higher than 20 ppb for SO

and higher than 10 ppb for NO

during both

flight days. The results seem to indicate that the high concentrations at low altitude

were a result of the transport of air pollution emission from China, while the high

concentration at 500 m was the result of strong wind from the west. The concentra-

tions of O

were greater than 80 ppb (and up to 110 ppb on April 18) at these altitudes

on both observation days. The lower concentrations of these species at higher alti-

tudes were related to the highest water mixing ratio. Lower concentrations of SO

and NO

were measured at an altitude of 1,000 m. The enhanced SO

concentration

occurred within the low-level westerlies in association with the anti-cyclonic flow

over southern China and the cyclonic circulation over Manchuria.

Table 7.2 Daily mean concentrations (ppbv) of SO

, NO

and O

during the measurement

periods

April (2005) October (2005)

15 16 17 18 21 15 16 17 19 22

(F1) (F2) (F4) (F3) (F1) Total (F1) (F2) (F3) (F4) (F1) Total

Mean 0.48 1.83 1.46 7.76 1.39 2.58 17.34 3.47 9.31 2.16 0.82 6.63

S.D. 0.40 1.86 0.66 6.75 1.07 10.52 1.53 7.84 1.93 0.37

Max. 1.20 9.25 3.63 21.47 4.98 35.94 6.73 30.38 9.09 1.81

Min. 0.01 0.02 0.49 0.26 0.13 2.17 1.15 0.47 0.11 0.06

Mean 2.11 2.77 2.84 9.14 4.36 4.24 6.71 3.30 3.37 4.00 1.14 3.74

S.D. 0.19 0.50 0.61 4.56 1.92 2.24 1.30 1.84 3.66 0.61

Max. 2.58 3.61 4.49 15.02 9.25 13.44 7.41 6.70 18.67 3.71

Min. 1.82 1.58 2.09 2.71 2.59 2.17 1.53 1.00 0.52 0.43

Mean 44 55 64 67 42 54 57 48 61 44 35 49

S.D. 3 5 5 26 4 11 4 19 5 3

Max. 49 63 72 118 52 69 56 91 64 44

Min. 39 47 52 36 36 38 42 34 30 28

F1, F2, F3 and F4 represent the different flight schedules, as shown in Fig. 7.2

98 S.-N. Oh et al.

0 5 10 15 20 25

500

1000

1500

2000

2500

3000

NOx

2 4 6 8 10121416

500

1000

1500

2000

2500

40 60 80 100 120

500

1000

1500

2000

2500

Altitude (m)Altitude(m)Altitude (m)

Concentration (ppb)

Fig. 7.4 Altitudinal distributions of the mass concentrations for SO

, NO

and O

on April 18, 2005

7 Aircraft Measurements of Long-Range 99

Concentration (ppb)

0 5 10 15 20 25 30 35

300m

500m

800m

1200m

1500m

1800m

2300m

2800m

NOx

02468

300m

500m

800m

1200m

1500m

1800m

2300m

2800m

20 40 60 80 100

300m

500m

800m

1200m

1500m

1800m

2300m

2800m

Altitude (m)Altitude (m)Altitude (m)

Fig. 7.5 Altitudinal distributions of the mass concentrations for SO

, NO

and O

on October 17, 2005

100 S.-N. Oh et al.

The longitudinal distribution of l-min average SO

and O

concentrations

decreased with the progress of the flight towards the Korean peninsula, as shown

in Fig. 7.6. The NO

concentration did not show any trend with flight progress

during the observation periods.

For source analysis to classify the pathway of the air mass, a divided northeast

region was applied to the backward trajectories of air pollution and revealed a

mostly northwest flow on the surface level, as shown in Fig. 7.7. The high concen-

tration of SO

was recorded when most of the air flow passed through region III

in April and region II in October (Fig. 7.8). The above pattern of SO

concentra-

tion was almost comparable to that of the urban atmosphere. After this episode of

high-SO

plume transport, SO

and aerosol number concentrations decreased

(a) (b)

Longitude (E)

124¡Æ 10'E 125¡Æ 30'E 127¡Æ E

Concentration (ppb)

NOx

Longitude (E)

124¡Æ 10'E 125¡Æ 30'E 127¡Æ E

Concentration (ppb)

1.0

1.5

2.0

2.5

3.0

3.5

Longitude (E)

124¡Æ 10'E 125¡Æ30' E 127¡Æ E

Concentration (ppb)

Longitude (E)

124¡Æ 10'E 125¡Æ 30'E 127¡Æ E

Concentration (ppb)

NOx

Longitude (E)

124¡Æ 10'E 125¡Æ 30'E 127¡Æ E

Concentration (ppb)

Longitude (E)

124¡Æ 10'E 125¡Æ 30'E 127¡Æ E

Concentration (ppb)

Fig. 7.6 Longitudinal distributions of mass concentrations for SO

, NO

and O

on April 16 (a)

and October 15 (b), 2005