Measurements of aerosol physical, chemical and optical parameters were carried out in Guangzhou, China from 1 July to 31 July 2006 during the Pearl River Delta Campaign. The dry aerosol scattering coefficient was measured using an integrating nephelometer and the aerosol scattering coefficient for wet conditions was determined by subtracting the sum of the aerosol absorption coefficient, gas scattering coefficient and gas absorption coefficient from the atmospheric extinction coefficient. Following this, the aerosol hygroscopic growth factor, f（RH）, was calculated as the ratio of wet and dry aerosol scattering coefficients. Measurements of size-resolved chemical composition, relative humidity （RH）, and published functional relationships between particle chemical composition and water uptake were likewise used to find the aerosol scattering coe？cients in wet and dry conditions using Mie theory for internally- or externally-mixed particle species [（NH_4）_2SO_4, NH_4NO_3, NaCl, POM, EC and residue]. Closure was obtained by comparing the measured f（RH） values from the nephelometer and other in situ optical instruments with those computed from chemical composition and thermodynamics. Results show that the model can represent the observed f（RH） and is appropriate for use as a component in other higher-order models.
A factor separation technique and an improved regional air quality model （RAQM） were applied to calculate synergistic contributions of anthropogenic volatile organic compounds （AVOCs）,biogenic volatile organic compounds （BVOCs） and nitrogen oxides （NOx） to daily maximum surface O3（O3DM） concentrations in East Asia in summer （June to August 2000）.The summer averaged synergistic impacts of AVOCs and NOx are dominant in most areas of North China,with a maximum of 60 ppbv,while those of BVOCs and NOx are notable only in some limited areas with high BVOC emissions in South China,with a maximum of 25 ppbv.This result implies that BVOCs contribute much less to summer averaged O3DM concentrations than AVOCs in most areas of East Asia at a coarse spatial resolution （1×1） although global emissions of BVOCs are much greater than those of AVOCs.Daily maximum total contributions of BVOCs can approach 20 ppbv in North China,but they can reach 40 ppbv in South China,approaching or exceeding those in some developed countries in Europe and North America.BVOC emissions in such special areas should be considered when O3 control measures are taken.Synergistic contributions among AVOCs,BVOCs and NOx significantly enhance O3 concentrations in the Beijing-Tianjin-Tangshan region and decrease them in some areas in South China.Thus,the total contributions of BVOCs to O3DM vary significantly from day to day and from location to location.This result suggests that O3 control measures obtained from episodic studies could be limited for long-term applications.
The Weather Research and Forecasting/Chemistry model （WRF-Chem） was updated by including pho- toexeited nitrogen dioxide （NO2） molecules, heterogeneous reactions on aerosol surfaces, and direct emissions of nitrous acid （HONO） in the Carbon-Bond Mechanism Z （CBM-Z）. Five simulations were conducted to assess the effects of each new component and the three additional HONO sources on concentrations of major chemical components. We calculated percentage changes of major aerosol components and concentration ratios of gas NOy （NOyg） to NOy and particulate nitrates （NO3-） to NOy due to the three additional HONO sources in the North China Plain in August of 2007. Our results indicate that when the three additional HONO sources are included, WRF-Chem can reasonably reproduce the HONO observations. Heterogeneous reactions on aerosol surfaces are a key contributor to concentrations of HONO, nitrates （NO3-）, ammonium （NH＋）, and PM2.5 （concentration of particulate matter of ≤2.5 um in the ambient air） across the North China Plain. The three additional HONO sources produced a -5% -20% increase in monthly mean daytime concentration ratios of NO3-/NOy, a -15%- 52% increase in maximum hourly mean concentration ratios of NO3-/NOy, and a -10% -50% increase in monthly mean concentrations of NOx and NH＋ across large areas of the North China Plain. For the Bohai Bay, the largest hourly increases of NO3- exceeded 90%, of NH＋ exceeded 80%, and of PM2.5 exceeded 40%, due to the three additional HONO sources. This implies that the three additional HONO sources can aggravate regional air pollution, further impair visibility, and enhance the incidence of haze in some industrialized regions with high emissions of NOx and particulate matter under favorable meteorological conditions.
