Airborne sub-pollen particles from rupturing giant ragweed pollen

Elizabeth A Stone,Dagen D Hughes,Chamari B A Mampage,Lillian M Jones

doi:10.1007/s10453-021-09702-x

Abstract

Ragweed pollen is a prevalent allergen in late summer and autumn, worsening seasonal allergic rhinitis and asthma symptoms. In the atmosphere, pollen can osmotically rupture to produce sub-pollen particles (SPP). Because of their smaller size, SPP can penetrate deeper into the respiratory tract than intact pollen grains and may trigger severe cases of asthma. Here we characterize airborne SPP forming from rupturing giant ragweed (Ambrosia trifida) pollen for the first time, using scanning electron microscopy and single-particle fluorescence spectroscopy. SPP ranged in diameter from 20 nm to 6.5 μm. Most SPP are capable of penetrating into the lower respiratory tract, with 82% of SPP < 1.0 μm, and are potential cloud condensation nuclei, with 50% of SPP < 0.20 μm. To support predictions of the health and environmental effects of SPP, we have developed a quantitative method to estimate the number of SPP generated per pollen grain ({n}_{mathrm{f}}) based upon the principle of mass conservation. We estimate that one giant ragweed pollen grain generates 1400 SPP across the observed size range. The new measurements and method presented herein support more accurate predictions of SPP occurrence, concentration, and air quality impacts that can help to reduce the health burden of allergic airway diseases.Graphic abstractRupturing ragweed pollen releasing cellular components (right), viewed by an inverted light microscope.

Highlights

When exposed to high humidity or water, pollen grains can become engorged with water and osmotically rupture to release sub-pollen particles (SPP) to the atmosphere (Miguel et al, 2006; Schappi et al, 1997; Taylor et al, 2002, 2004)
Pollen rupturing was induced by misting flowering sprigs of giant ragweed with a fine spray of water at five-minute intervals, as indicated by the instantaneous appearance of fluorescent sub-micrometer SPP (Fig. 1a)
The peak SPP number concentrations in the chamber (0.3–0.5 cm-3) were within the range of those observed in ambient air during convective thunderstorms (0.3–1.3 cm-3) by the same instrument (Hughes et al, 2020), indicating that environmentally relevant concentrations of SPP were produced in the chamber

Summary

Introduction

When exposed to high humidity or water, pollen grains can become engorged with water and osmotically rupture to release sub-pollen particles (SPP) to the atmosphere (Miguel et al, 2006; Schappi et al, 1997; Taylor et al, 2002, 2004). A single value for nf was reported by Suphioglu et al (1992) for a single rye grass pollen grain, which formed 700 SPP greater than 0.6 lm in diameter upon rupturing This value provides an incomplete description of SPP, as field and laboratory studies demonstrate high concentrations of SPP with diameters \ 0.6 lm (Hughes et al, 2020; Taylor et al, 2002, 2004). This single value does not account for variations in nf across plant taxa, seasonal, or environmental conditions, which affects pollen grain shape, size, and composition. We characterize SPP released from giant ragweed (Ambrosia trifida) for the first time and develop and apply a new method to calculate nf from measurements of SPP

Materials and methods

Characterization of giant ragweed SPP

Method for determining the number of pollen fragments generated per pollen grain (nf)

Determination of nf for giant ragweed