The lifetime of aerosols in ambient air: Consideration of the effects of surfactants and chemical reactions

Abstract

Rev. Hegg and Hobbs. 197g; t!I rldl eton P.t a 1. 1980).These wet processes are suggested to be important in the formation of atnospheric sulfate and nitrate particulates in clowis anrl thus contribute to an increase in the acirlity of rain. pH levpls as low as 2.::> 11ere founrl in a recent study of Los 1\n:Jeles fog rlroplets (LA Tir'les. 9/?4/H2).In the post. the assess•nent of the inpact of "''et cheMica 1 processes hns heen 1aruely haserl on the cherlica1 reaction r(!tf'<>. HoNeVE'r. '"tH~n relative hnnirlity is le.:;s than 1mity. riroplets evapornte and thP reaction ri'lte is limited hy the aerosols 1 Pvnrorat.ion time. Ther~>fore in this paper, the lifeti1'1e of these rlror1Pt'i is deter11i ned anrl used to assess the if'lpnrtance of nquen11S reactions undf"r Atnospheric conditions.The lifetine 0f rlrop1ets is prolonged ilt <1 given rel<'itive humidity hy the presence of hygroscopic St'llt nuclei and hy surfi'lctant rnatf'rial forr1erl into n fi 1m on their surf aces. The presP.nce of i nso 1 uh 1 e nateri a 1 (!Ccentuates this effect by acting as a condensation stJrfacE> for tracP inp11rities and by increasing H 1 P concentration of salt, resulting in a lesser requin'!d amount of 1·1ater for a given size rlroplet to forme f:loud anrl fog saf'lples collected by Kuroh1a (1951, 195S) nnd Ogiwilra and Okita (1952) were found to contain soluble and insoltlhle particles ':Jhich werf' similar in nature, form, and size to those prod11Ced hy haze i'lnrl cornhll';tion.The presence of these ir1p11rities in samples of atmospheric liquid water hfis also heen suhstantii'ltect (lfinl<lPr, 1973; Covert et al, 1472 Tahle ?). llnrlf'r t.hese conrlitions, f'lquation ( 1) can he solved to givP thf' lHeti11P. as:In Fig11re pl;wsihle that they could h~ responsiblf" for the production of the major part of sulfate in fogs and clot~ds and in the formation of acirl rain (Chang et al~ l9Rl). 5The conditions unrler which onf" or all of these oxidation processes are iMportant depend on the meteorological paraneters and on the concentration of gaseous species in the at1nospbere 9 as wf>ll as on the nature and availahility of an oxirli1ing i'l9ent. Liquid ~rlfiter is neerled to initinte the reaction, which can hf> ilCqtlin~cJ hy physical flhsorption on tlw Sttrfnce of ,;m inc;oluble solirl or hy hy\Jroscopic solt1hlP salt ntJclei in the aerosol.\~hPther the ratP. of so 2 convPrc;ion is controllerl hy the rate of diffusion of yaseous po'lltAtants t01-1ard i'\nrl ,.

Fatty acids in the marine atmosphere: Factors governing their concentrations and evaluation of organic films on sea‐salt particles

“…Third, they could reduce the scavenging efficiency of particles by larger cloud and raindroplets [e.g., McDonald , 1963]. In the last case, the organic films would increase the atmospheric lifetime of aerosol particles compared to those expected if the films were not present [ Toossi and Novakov , 1985].…”

Solubility properties of surfactants in atmospheric aerosol and cloud/fog water samples

“…The lowered surface tension of cloud droplets may affect their coagulation rate, and consequently rain formation. It also affects the aerosol scavenging efficiency of raindrops [ Toossi and Novakov , 1985]. Another effect of films is to provide a barrier to the exchange of gases between the gas and bulk liquid phase.…”

Oxocarboxylic and .alpha.,.omega.-dicarboxylic acids: photooxidation products of biogenic unsaturated fatty acids present in urban aerosols

“…Long-chain carboxylic acids in their salt form may be considerd as surfactants in aqueous atmospheric aerosols that form an organic coating over the aerosol surface (21) and thus may increase the lifetime of such particles in the atmosphere. Therefore, in this mixed (marine and land derived) urban aerosol, unsaturated acid salts possess long enough time to be oxidized by various atmospheric oxidants to form the detected oxo-and dicarboxylic acids in concentrations higher than those found in the free form.…”