Aerosol Effects on Fog and Rain Formation in the

Tropical Pre-Montane Wet Forest of Costa Rica

Kaitlin Cloud, Josh Mallin, and Dr. Sarah Brooks

Department of Geography, Texas A&M University

Daily fog and rain samples were collected with a passive fog collector and

rain gauge (Figure 2)

pH and surface tension of samples were analyzed

Daily particle counts were taken with an TSI AEROTRAK Handheld particle

counter

Vertical aerosol profiles were taken at 7 sites under different weather

conditions using a telescoping pole (Figure 3)

• Water samples were analyzed via:

Raman Spectroscopy (chemical composition)

Cavity Ring Down water isotope analyzer (isotopic composition)

Cloud Condensation Nuclei Counter (critical supersaturation point

Methods

The ecohydrology of the Costa Rican pre-montane wet forest provides

valuable information about human influence on montane cloud forests. Fog

and rain formation is a crucial part of the hydrologic cycle in tropical forests.

Our research focuses on how biogenic and anthropogenic aerosols affect

the formation of fog and rain. This study aims to:

Quantify fluctuations in aerosol concentrations, spatially and temporally

Determine the composition of aerosols in fog and rain

Identify sources of aerosols

Ascertain the cloud nucleation properties of various aerosols

Introduction

Fine and coarse aerosols fluctuate differently from each other temporally

and spatially. These differences are seen in the vertical profiles and the daily

counts.

Vertical profiles show large spatial deviations despite the close proximity of

site locations.

June 29th and July 13th and 14th were identified as “event days” with

significantly high aerosol concentrations.

The Raman spectra indicate the presence of multiple organic compounds in

the fog water samples.

Preliminary isotope data indicates that the isotopic ratios vary with air mass

source, and can be used to identify the source of a weather event.

Future Work

Identify causes of event days, comparing to weather data

Analyze Raman spectra and compare to spectral libraries and known

standards

Conduct further isotopic analysis and correlate to aersol data

Conclusions

Research was supported by a grant from the National Science Foundation. Field assistance was provided by Dr. Chris Houser

and Kelly Lemmons. Weather data provided by Arelis Riviera and Samantha Wills.

Acknowledgements

Figure 2. Passive fog collector with

rain gauge.

Figure 3.

Particle count

pole

extensions at

two sites –

under canopy

and in a

clearing.

Location

Figure 1. Map of research area.

Site A: covered canopy. Site B:

open canopy. Site C: open

canopy. Site D: covered canopy.

Site E: covered canopy.

N

0

50000000

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0 2 4 6 8 10 12 14 16 18 20

Part

icle

co

un

t (m

-3)

Sample Number

Site D Fine Particles 27-Jun

28-Jun

29-Jun

1-Jul

2-Jul

3-Jul

4-Jul

5-Jul

6-Jul

7-Jul

11-Jul

13-Jul

14-Jul

16-Jul

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icle

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-3)

Sample number

Site D Coarse Particles 27-Jun

28-Jun

29-Jun

1-Jul

2-Jul

3-Jul

4-Jul

5-Jul

6-Jul

7-Jul

11-Jul

13-Jul

14-Jul

16-Jul

Particle Count Results – Vertical Profiles

0

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�14 cm �141 cm �245 cm �364 cm �493 cm �652 cm �763 cm �907 cm 1062 cm

Aero

so

l C

on

cen

trati

on

(m

-3 )

Fine Aerosols (Sites 1-4)

6-Jul

14-Jul

16-Jul

17-Jul

18-Jul

19-Jul (11:00AM)

19-Jul (2:00PM)

19-Jul (4:30PM)

21-Jul

-1000000

1000000

3000000

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9000000

11000000

13000000

�14 cm �141 cm �245 cm �364 cm �493 cm �652 cm �763 cm �907 cm 1062 cm

Aero

so

l C

on

cen

trati

on

(m

-3)

Coarse Aerosols (Sites 1-4)

6-Jul

14-Jul

16-Jul

17-Jul

18-Jul

19-Jul (11:00AM)

19-Jul (2:00PM)

19-Jul (4:30PM)

21-Jul

0

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0 200 400 600 800 1000 1200

Aero

so

l C

on

cen

trati

on

(m

-3)

Heights (cm)

Fine Aerosol Profiles

Site 1

Site 2

Site 3

Site 4

0

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(m

-3)

Heights (cm)

Coarse Aerosol Profiles

Site 1

Site 2

Site 3

Site 4

Chart 1. Concentrations of fine (≤1μm) and coarse aerosols (>1μm ) at different heights at our four primary particle

profiling locations, averaged over the seven days sampled.

Chart 2. Changes in fine and coarse suspended particle concentrations at increasing heights above ground,

averaged over our four primary profiling locations.

CF7-11

EF7-11

AF7-11

CF7-12

EF7-11

AF7-13

Table 1. Isotopic ratios of fog and rain

samples from all sites and 4 days.

Sample δ18O δ2H

AR 6/29 -9.18 -56.16

BR 6/29 -9.33 -55.94

CR 6/29 -8.81 -52.80

DR 6/29 -8.99 -52.60

ER 6/29 -9.08 -53.38

AR 7/4 -12.84 -86.58

BR 7/4 -12.28 -82.22

CR 7/4 -12.95 -85.88

DR 7/4 -13.38 -89.13

ER 7/4 -13.28 -86.50

AR 7/13 -15.25 -106.17

BR 7/13 -16.55 -117.58

CR 7/13 -16.37 -117.73

DR 7/13 -15.76 -111.74

ER 7/14 -15.99 -114.80

CF 7/4 (fog) -12.35 -81.94

δ18O δ2H

Sea Water -1 to 0.6 -2.5 to 3.2

Continental Water -62.8 to 31.3

-495 to 129

Table 2. Isotopic ratios of known water

sources globally. Taken from USGS Water-Resources

Investigation Report, Aug 2002

Particle Count Results – Daily Counts

Daily particle

counts show

significant temporal

variation in aerosol

concentrations.

Temporal

variations of fine

and coarse particles

do not correlate,

indicating that they

come from different

sources.

Raman Spectroscopy Results

Isotopic Ratios

Raman Spectra

indicate the

presence of a

variety of organic

compounds in the

fog water.

The chemical

composition of the

fog water varies

by day and by

site. Chart 4. Raman spectra of 6 fog samples from 3 sites and 4

different days. The second image is a magnified version of the first.

Chart 2. Daily 20-min. particle counts were taken at each site.

Chart 1 shows the apparent differences in profiles measured at the four sites of the

lower elevation clearing zone.

The variability in aerosol concentration on different sampling days is emphasized in

Chart 2.

There is a visible difference in fine aerosols and coarse aerosols at various sites and

on various days.

Isotopic ratios vary

significantly over time but not

spatially.

Isotopic ratios of precipitation

depend on the source of the air

mass.

Event Day